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Terms
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Definitions
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What are the 4 most commonly
occurring elements in living things?
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Carbon, hydrogen, oxygen,
nitrogen.
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What are 5 other elements living
things require?
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Sulfur, calcium, phosphorus, iron,
sodium.
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What is the function of sulfur?
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Used in proteins in prokaryote,
animal and plant cells.
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What is the function of calcium?
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Flagella movement in prokaryotes
forms cell plate during cytokinesis in plants, used in shells, bones, teeth
and vesicle fusion in animals.
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What is the function of
phosphorus?
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Nucleic acids and ATP in animals,
plants and prokaryotes.
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What is the function of iron?
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Cytochrome (used in respiration)
in palnts, and in cytochrome for mitochondrial respiration in plants and
animals, hemoglobin.
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What is the function of sodium?
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Main cation in cytoplasm of plant
cells, nerve impulse transmission in animals.
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Why is water polar?
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Because it has positive and
negative ends/poles.
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Why is water cohesive?
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Because the negative end of one
molecule's oxygen can form a hydrogen bond with the positive hydrogen of
another molecule.
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What can be said about water's
specific heat capacity?
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It is high i.e. it can store a lot
of heat.
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What solvent property is water
given by its polarity?
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It can dissolve other polar
molecules and ions such as sugars, amino acids and sodium ions.
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Give the three main functions of
water in organisms.
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Coolant, medium for metabolic
reactions and a transport medium.
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Why can water be used as a
coolant?
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It requires a high input of energy
to break the hydrogen bonds and turn it into a vapour; so, evaporation of
water off of the surface of an organism allows it to lose heat.
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Give an example of water being
used as a coolant.
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Plants in deserts increase transpiration
when in danger of overheating.
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Why can water be used as a medium
for metabolic reactions?
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It is a good solvent, and is a
liquid between 0-100 degrees centigrade, the temperature in most regions of
the Earth.
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What function does a watery
habitat serve for organisms?
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It dissolves substances which can
then be absorbed by organisms.
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What function does a watery
cytoplasm serve for organisms?
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It dissolves substances, and
metabolic reactions can take place easily between substances dissolved in a
liquid medium.
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Why can water be a transport
medium?
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Its high specific heat capacity
means it can store heat energy, and so organisms use if for heat transport
(e.g. in blood). It is a good solvent and a dense medium, so it can dissolve substances
and support heavy particles, and the cohesive property of water creates the
transpiration stream in plants.
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What are organic compounds?
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Those that contain carbon and are
found in living organisms.
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What do organic compounds not
contain?
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Carbonates, hydrogencarbonates and
oxides of carbon.
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What do amino acids contain?
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Nitrogen and a variable R side
group.
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How many amino acids are there
which are used in proteins?
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20.
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What is the formula of glucose?
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C6H12O6
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What is the formula of ribose?
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C5H10O5
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What functional groups do fatty
acids have?
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A CH3 on one side and a COOH on
the other.
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How many CH2 groups are there in
fatty acids?
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Variable, but usually between 12
and 22.
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What other groups can fatty acids
have?
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CH groups with double bonds
between adjacent carbons.
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What is an unsaturated fatty acid?
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One with double bonds.
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What is a saturated fatty acid?
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One without double bonds.
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What is a polyunsaturated fatty
acid?
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One with a large number of double bonds.
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What are the three main types of
carbohydrate?
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Monosaccharides, disaccharides,
polysaccharides.
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Name 3 monosaccharides.
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Glucose, galactose, fructose.
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Name 3 disaccharides.
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Maltose (2xglucose), lactose
(glucose+galactose), sucrose (glucose+fructose).
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Name 3 polysaccharides.
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Starch, glycogen, cellulose (all
poly-glucose).
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Give a function of glucose.
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It is broken down in animal
respiration to release energy.
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Give a function of lactose.
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It is a sugar in milk produced by mammals.
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Give a function of glycogen.
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It is an energy store in liver and
skeletal muscles.
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Give a function of fructose.
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It is an energy source for plants
and a component of sucrose.
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Give a function of sucrose.
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It is un reactive and so is transported
around the plant.
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Give a function of cellulose.
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It is the main component of cell
walls.
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What happens during condensation?
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2 units are joined together with
the release of water.
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What happens during hydrolysis?
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2 units are separated using water.
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What are 6 functions of lipids?
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Cuticle on leaf to prevent water
loss, thermal insulation in animals as sub-cutaneous fat, energy store in
plants and animals, oil on feathers and fur for water-proofing, main
component of myelin sheath of neurons, buoyancy in aquatic animals.
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Give 4 features of using
carbohydrates as energy stores.
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17kJ/g energy released, easily
built up and broken down, present as glycogen in animals and starch in
plants, converted to glucose when energy is needed.
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Give 4 features of using lipids as
energy stores.
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38kJ/g energy released, hence more
efficient than carbohydrate, hydrophobic, so less mass taken up storing
water, metabolic pathways for build up and breakdown more complex and slower,
converted to fatty acids and glycerol when energy is needed, then to coenzyme
A.
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What are the three parts of a
nucleotide?
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A phosphate group, a deoxyribose
sugar and a base.
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What links the sugar to the base
and phosphate?
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Strong covalent bonds.
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What are the four bases in DNA?
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Adenine, thymine, cytosine,
guanine.
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How does the double helix form?
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Complementary base pairing (A-T,
C-G), where the 2 sugar phosphate chains are anti-parallel. Weak hydrogen
bonds form between the bases to hold the chains together.
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What are cytosine and thymine?
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Pyramidines.
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What are adenine and guanine?
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purines.
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How many hydrogen bonds does the
A-T connection have?
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2.
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How many hydrogen bonds does the
C-G connection have?
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3.
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What directions do the DNA strands
have?
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One is 5'-3', the other is 3'-5'.
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What does 5' mean?
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Carbon 5 of the sugar has a
phosphate attached and nothing else - it is a 'free end'.
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What does 3' mean?
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Carbon 3 contains a hydroxyl group
and is the other 'free end'.
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What is linked to the 5 and 3
carbons?
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The sugars.
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What do nucleosomes consist of?
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A group of histone proteins with
the DNA wrapped around; the DNA is locked in place by a second type of
histone.
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What are the 2 functions of
nucelosomes?
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They help supercoil the
chromosomes and help to regulate transcription.
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What are the 2 types of nuclear
DNA?
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Unique or single-copy genes and
highly repetitive sequences.
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What does 55-95% of the DNA
consist of?
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Sequences, called genes that only
have a single copy.
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What do the single-copy genes code
for?
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The functional polypeptides used
by the cell or body, such as structural proteins, transport proteins,
enzymes, hormones.
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What does 5-45% of the DNA consist
of?
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Highly repetitive sequences.
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What are highly repetitive
sequences?
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They can be 5-300 base pairs long,
and can be repeated a moderate number of times, or up to 10^5 times in a
genome. The location of these sequences shows no apparent patter, and their
function is generally unclear.
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What can we use the highly
repetitive sequences for?
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DNA profiling.
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What else do eukaryotic genes
contain?
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Introns and exons.
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Is DNA replication conservative or
semi-conservative, and what does this mean?
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Semi-conservative; the DNA double
helixes produced will both contain one strand of the old DNA and one new
strand.
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What is the first step of DNA replication?
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DNA helicase unwinds the DNA
double helix by breaking the bonds between the bases; this forms the
replication fork.
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what does DNA polymerase III do?
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It adds on new nucleotides to
create the complementary strand of DNA, with hydrogen bonds between the
bases, i.e. adds deoxynucleoside triphosphates to the 3' end.
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What is the genetic code?
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The linear sequence of bases.
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How is the genetic code preserved?
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By complementary base pairing.
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What direction does DNA
replication occur in?
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5'-3'.
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What does RNA primase do?
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Adds nucleoside triphosphates on
the lagging strand to form an RNA primer.
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What does DNA polymerase I do?
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Removes the RNA primer, replaces
it using deoxynucleoside triphosphates.
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What does DNA ligase do?
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Joins the Okazaki fragments
together.
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What are Okazaki fragments?
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Short lengths of single-stranded
DNA made on the lagging strand.
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What are deoxynucleoside
triphosphates?
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The building blocks of DNA;
consist of the deoxyribose sugar, with a base and three phosphates.
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What happens when the
deoxynucleoside triphosphates are attached to others in DNA synthesis?
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The two phosphates are removed,
leaving only one for the sugar-phosphate backbone.
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What are nucleoside triphosphates?
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The molecules used to synthesise
RNA, which is the same thing with ribose sugar instead.
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Does DNA replication occur at one
point only?
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No - it is initiated at many
points within eukaryotic chromosomes.
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What are the 3 structural
differences between RNA and DNA?
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RNA is single stranded (but can
fold back on itself to form double-stranded regions), has the base uracil
instead of thymine, and has the sugar ribose instead of deoxyribose.
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What are the 3 main differences of
transcription compared to DNA replication?
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Only one strand of the DNA is
copied, RNA nucleotides are used (there is a pool of these in the nucleoplasm),
the enzyme RNA polymerase is used.
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What are the 3 key steps of
transcription?
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DNA is unzipped by RNA polymerase,
RNA polymerase builds mRNA by pairing mRNA nucleotides onto the strand of DNA
opposite the desired gene, mRNA is released and leaves the nucleus.
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How many RNA bases code for one
amino acid?
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3.
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How many codes are there for stop
codons?
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3.
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What are stop codons?
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Markers of the end of the
'message' on mRNA.
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How many codes are there in total?
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64.
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What is degeneracy?
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When two codes code for the same
amino acid.
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Why is the code universal?
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Because all organisms use this
same code.
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What is translation?
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The process used to manufacture a
polypeptide chain from the mRNA code.
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What direction does transcription
occur in?
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5'-3'.
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What is the sense strand?
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The side of the DNA double helix
that is a gene.
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What is the antisense strand?
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The complementary sequence of
bases, which is transcribed into RNA.
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Which strand has the same sequence
of bases as the RNA strand?
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The sense strand, replacing T with
U.
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What is the promoter region?
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A specific sequence of DNA bases
at the start of a gene on the sense strand where RNA polymerase binds.
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What is the purpose of RNA
polymerase?
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Adds nucleoside triphosphates
using base pairing to the DNA template. It can only bind to DNA in the
presence of other special proteins made by genes elsewhere in the genome.
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What does the RNA polymerase do as
it moves forwards?
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It unwinds and separates the DNA
at the front, and rewinds it at the back.
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When does the RNA separate from
the DNA?
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As it is synthesised.
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What is the terminator region?
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A specific sequence of DNA bases
marking the end of the transcription process on the sense strand.
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What happens to the RNA polymerase
when it reaches the terminator region?
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It breaks free and the mRNA is
released.
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What does primary RNA contain?
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Introns.
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What are introns?
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Sequences that are not translated
into part of the protein, and must be removed.
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What do the exons do?
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They make up the mature RNA.
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Where does the
post-transcriptional modification of mRNA take place?
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In the nucleus.
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How many types of tRNA are there?
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61, as there are 61 codons
(excluding stop codons).
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Where does the amino acid join on
the tRNA?
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At the 3' end.
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What does adding the amino acid
require?
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Energy from ATP and a specific
enzyme.
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What are ribosomes composed of?
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Ribosomal RNA and protein, in two
subunits.
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What does the small subunit of the
ribosome do?
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Binds to the mRNA.
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What does the large subunit of the
ribosome do?
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Has three binding sites to bind to
tRNA.
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Where are ribosomes manufactured?
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In the nucleolus within the
nucleus.
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What are the 4 stages of
transcription?
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Initiation, elongation,
translocation and termination.
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What happens during initiation?
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The small ribosome subunit binds
to mRNA and the first charged tRNA binds to the start codon (charged means it
has an amino acid attached).
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What is the start codon in
prokaryotes?
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AUG.
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What does initiation form?
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The initiation complex.
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Where does initiation take place?
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In the cytoplasm, where the
ribosomal subunits are.
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What happens during elongation?
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The large ribosome subunit
attaches so that the 1st charged tRNA is in binding site 1 (in the middle).
The second charged tRNA binds in the second binding site (on the right). A
peptide bond is formed between the two amino acids.
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What is a peptide bond?
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A bond between the C of a C=O and
the N of an N-H.
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Where is the polypeptide
synthesised if it is designed for expot?
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on the rER.
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How is it known that a polypeptide
is for export?
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The first part of the polypeptide
is a signal that causes the ribosome to bind to the rER.
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What happens to the polypeptide as
it is released if it has been synthesised on the rER?
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It is passed through a protein
channel in the rER.
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What happens during translocation?
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The mRNA is moved along one codon,
and so the ribosome has moved along one codon in the 5'-3' direction. The
uncharged tRNA is now in the 3rd site and is separated from the mRNA. It
breaks free and picks up another amino acid from the cytoplasm. The 3rd
charged tRNA moves into the 2nd binding site, and this process repeats.
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What happens during termination?
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The ribosome reaches the stop
codon. There are no tRNAs with an anticodon for a stop codon. Release factors
bind to site 2, and the ribosome subunits break free and the polypeptide is
released.
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What kind of polypeptides do free
ribosomes synthesise?
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Those primarily for use within the
cell and cytoplasm.
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What kind of polypeptides do
ribosomes bound to the rER synthesise?
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Those primarily for secretion or
lysosomes.
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How does the cell overcome the
need to produce many polypeptides in large quantities?
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As it would be energetically
inefficient for each mRNA to synthesis only one polypeptide before being
destroyed, ribosomes join behind the first ribosome so that multiple copies
of the polypeptide can be synthesised rapidly.
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What are enzymes?
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Large molecules folded to form a
3-dimensional globular structure that act as catalysts.
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What is an enzyme's active site?
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A specifically shaped
"pocket" for that enzyme's substrate to fit into. The shape of the
active site matches the shape of the substrate, so that substrates are
brought together in the correct orientation.
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What happens to the bonds in
substrates when bound to an enzyme?
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They are weakened, making a
reaction easier.
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Which 3 factors affect enzyme
action?
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Substrate concentration, pH,
temperature.
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How does substrate concentration
affect enzyme action?
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Amount of enzymes, and therefore
active sites, is fixed. As substrate concentration increases, more collisions
occur with the enzymes and so more reactions occur. At a point, all the
active sites are occupied by substrate at any one time, and so there can be
no further increases in reaction rate.
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How does pH affect enzyme action?
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The 3D shape of the enzyme is held
in place by bonds, which are strongest at the optimum pH. Changing the pH
affects these bonds and the shape of the active site; if the substrate can no
longer bind to the active site, reaction rate drops.
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How does temperature affect enzyme
action?
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Temperature increases the
molecular movement, and so the molecules in the solution collide with more
energy, so more reactions occur. However, beyond the optimum temperature, the
amino acids in the protein are moving so much that weak bonds are broken and
the molecule begins to fall apart. The shape of the active site no longer
fits the substrate and the reaction cannot take place.
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Define "denaturation"
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The irreversible, structural
change in an enzyme that makes it unable to catalyse due to the substrate no
longer fitting its active site.
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Give a practical use of enzymes.
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Production of lactose-free milk.
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Why is lactose-free milk needed?
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Some adults are intolerant to
lactose, as the gene producing lactase gets switched off with age, and as
lactose is a disaccharide it cannot be absorbed in the gut. The lactose is
then fermented by bacteria in the large intestine resulting in nausea,
abdominal pain and diarrhea.
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How can milk be made lactose-free?
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It is treated with lactase; this
breaks down lactose to the monosaccharides glucose and galactose, which are
easily absorbed by the gut.
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Where is the lactase obtained
from?
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The fungus Kluyveromyces lactis.
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Practically, how is the milk
treated with lactase?
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The lactase is immobilized and the
milk is passed over it; this prevents the lactase from being in the product
and is more economical, as it can then be reused.
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What are 3 commercial applications
of lactose-free milk?
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Making ice cream (lactose
crystallises and makes the ice cream grainy, whereas glucose and galactose
stag dissolved). Yoghurt production, as bacteria can ferment glucose and
galactose quicker than lactose, making production quicker. Lactose is also
less sweet-tasting than glucose and galactose, so using lactose-free milk
means less added sugar has to be added to products.
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What do metabolic pathways consist
of?
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Chains and cycles of
enzyme-catalysed reactions.
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What does the "induced-fit
model" mean?
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The shape of the active site only
corresponds to the shape of the substrate once it binds, which prevents
possible but undesirable substrates from binding. The active site is
flexible, so it allows a group of related molecules with similar shapes to be
able to bind (e.g. peptidases). The reduces the number of different types of
enzymes needed.
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What is needed for a reaction to
occur?
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The necessary activation energy.
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What do enzymes do to the
activation energy?
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They lower it, so that the
reaction can take place at lower physiological temperature (usually between 0
and 40 degrees celsius).
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What are the two types of enzyme
inhibition?
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Competitive and non-competitive.
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What happens in competitive
inhibition?
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The substrate and inhibitor have
similar shapes and compete for the active site.
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What is an example of competitive
inhibition?
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In the liver, the metabolic
pathway is: ethanol -> acetaldehyde -> acetate. Aldehyde dehydrogenase
is the enzyme to convert acetaldehyde to acetate. Disulfiram is a drug used
to help recovering alcoholics; it blocks the active side of aldehyde
dehydrogenase, so acetaldehyde is not broken down in the liver and its
accumulation in the blood causes severe headaches and nausea.
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What happens in non-competitive
inhibition?
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The inhibitor has its own binding
site, and binding of the inhibitor causes a conformational change in the
shape of the active site, preventing the binding of the substrate.
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Give an example of non-competitive
inhibition.
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Enzyme: acetylcholinesterase,
substrate: acetylcholine, inhibitor: nerve gas Sarin.
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What is the difference in effect
of non-competitive and competitive inhibition at high concentrations?
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Non-competitive inhibition will
always reduce the rate of reaction at any concentration as the inhibitor
binds to a separate site, whereas at higher substrate concentrations, the
concentration of a competitive inhibitor becomes so low that it has no effect.
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Where is non-competitive inhibition often used in the body?
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To regulate metabolic pathways.
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What are enzymes that are inhibited non-competitively in metabolic
pathways called?
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Allosteric enzymes.
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What is the inhibitor for
allosteric enzymes called?
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The effector.
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How do allosteric enzymes work?
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The enzyme has two subunits, one
with the substrate active site and the other with the allosteric site, where
the effector binds (there may be more than one of these). The enzyme can
alternate between an active form, which reacts with the substrate, and an
inactive form, which does not. The effector can be an activator or inhibitor
of the enzyme: the activator stabalises the active form, and the inhibitor
stabalises the inactive form.
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Give an example of an allosteric
enzyme.
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Phosphorylase is an enzyme in
muscle which removes a glucose phosphate from the end of glycogen at the
start of glycolysis. If the muscle is resting, its relative concentration of
ATP will be high. If it is active, it will use up ATP and its relative
concentration of AMP (adenosine monophosphate) will be high. AMP is the
activator and ATP is the inhibitor; the enzyme is thus regulated so that
glycogen is not broken down unnecessarily.
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