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Parts of nucleotides (3)
pentose sugar with 5 carbon atoms
phosphate group : acidic and negatively charged part of nucleic acids
base that contains nitrogen - has either 1 or 2 rings of atoms in its structure
Strands of DNA nucleotides in relation to each other (2)
(anti)parallel - parallel but run in opposite directions
one strand ends with phosphate group other ends with deoxyribose (pentose sugar)
Differences between DNA and RNA (3)
DNA is double-stranded, RNA is single-stranded
RNA has uracil instead of thymine in DNA
pentose sugar of DNA is deoxyribose, pentose sugar of RNA is ribose
Define a purine (3)
Adenine
Guanine
have 2 carbon rings
Define a pyrimidine (4)
Thymine
Cytosine
Uracil
has one ring
Appearance of nucleosome (2)
length of DNA wrapped twice around cores of 8 histone molecules (2 copies of 4 different histones)
additional histone molecule (H1) reinforces binding of DNA to nucleosome core
How are chromosomes formed from nucleosomes (3)
nucleosomes joined together by linker DNA
nucleosomes stacked onto each other
stacks form chromosomes
Purpose of the Hershey-Chase experiment
proving that DNA made up genetic material instead of protein
Materials used in the Hershey-Chase experiment (3)
virus - T2 bacteriophage
bacteriophage inner DNA coated in radioactive phosphorous
bacteriophage outer protein coated in radioactive sulfur
Hershey-Chase experiment results (3)
bacteriophages with radioactive phosphorous infected non-radioactive bacteria, all infected cells became radioactive
next-generation of bacteriophages produced from infected bacteria were all radioactive
bacteriophages coated in radioactive sulfur + virus coats separated = no radioactivity inside infected cell
Describe Hershey-Chase experiment (5)
bacteriophage added to bacteria
blender separates bacteriophage capsid from DNA in bacteria
centrifuge separates bacteriophage from virus to allow investigator to detect radiation location
Phosphorous - virus capsid in liquid is not radioactive, bacteria are
Sulfur - viruse capsid in liquid are radioactive, bacteria are not
Chargaff’s experiment (3)
extracted DNA from cells + mixed them with acid
acid breaks bonds between pentose sugar + base
bases separated using paper chromatography + concentration of bases measured
Chargaff’s results (2)
concentration/amount of adenine equal/similar to thymine
concentration/amount of cytosine equal/similar to guanine
Importance of Chargaff’s experiment (3)
hinted at complementary base pairing
helped watson and crick build their double helix model
dispelled tetranucleotide hypothesis
Tetranucleotide hypothesis (2)
DNA contains repeating sequence of 4 bases (4 nucleotides occur in equal amounts)
DNA was single-stranded
Condensation Polymerisation (3)
two molecules join together
one molecule loses a hydroxyl group (-OH), another loses a hydrogen atom (-H)
causes formation of water
Describe a glycosidic bond
oxygen atom shared between 2 glucose molecules
Define hydrolysis (2)
chemical reaction where water is used to break covalent bond between monomers
-OH will attach to one monosaccharide, -H will attach to other
Isomers of glucose (2)
alpha-glucose
beta-glucose
Orientation of alpha-glucose (2)
hydroxyl group (OH) is orientated downward
e.g glycogen + starch
Orientation of beta-glucose (2)
hydroxyl group (OH) is orientated upward
e.g cellulose
Properties of glucose (3)
glucose is soluble + small –> easily transported
glucose is chemically stable
yields energy when oxidised
Why glucose is soluble (4)
soluble because it is polar
contains (-OH) molecules which are polar
oxygen atoms are partially negative
so carbon-hydrogen (C-H) atoms are partially positive
Applications of glucose being soluble (2)
polar so able to dissolve in water
dissolves in plasma - can be transported in blood, OH groups bond with water in plasma
Why is glucose chemically stable (2)
ring structure - atoms are bonded to minimise strain + allows for strong covalent bonds
hydroxyl groups - forms bonds with water molecules (stable in aqueous solution) + prevents glucose from undergoing reactions
Application of property of glucose being chemically stable (2)
improves structural role of cellulose in plants
helpful in starch and glycogen for storage
Oxidisation as a property of glucose (3)
addition of oxygen to a molecule
loss of hydrogen atom
loss of electrons to another atom/ion
Application of glucose property of being easily oxidised (2)
oxygen important reactant for cellular respiration
broken down by losing electrons to oxygen to form CO2 and H2O
Name 2 types of starch (2)
amylose
amylopectin
Describe amylose (2)
polysaccharide made of glucose monomers linked through alpha-1,4 -glycosidic bonds
helical shaped chain
Describe amylopectin (2)
polysaccharide made up of glucose monomers linked through alpha-1,4-glycosidic bonds with ocassional 1,6-glycosidic bonds
branched shaped chain
Amylopectin property (3)
branch shape allows amylopectin to be more packed together - allows for more efficient storage of glucose
adding + removing glucose is quicker since branch shape has more ends
major component of starch
Starch properties (2)
compact in structure due to branching and coiling - efficient storage for small space
insoluble due to large size - can store lots of glucose, ensures that water is not drawn in
Describe maltose
disaccharide formed from 2 alpha-glucose molecules joined by a glycosidic bond
Describe sucrose
alpha-glucose molecule and fructose molecule joined by a glycosidic bond
Describe lactose (2)
glucose + galactose molecule
joined by glycosidic bond
Describe the structure of glycogen (2)
linear glucose chains linked through alpha 1,4 glycosidic bonds and 1,6 glycosidic bonds
forms compact coiled structure
Features of glycogen (2)
insoluble due to large molecular size - does not affect osmotic concentration of cells
branched structure - can be easily hydrolysed to produce glucose
Cellulose characteristics (3)
structural sugar in plants
strong - hydrogen bonds between chains create lattice structure
1,4 glycosidic bond
Cellulose structure (4)
straight chain of beta-molecules
B-glucose is inverted so that -OH groups are together
hydrogen bonds form between chains (polarity between O in glycosidic bond + H in glucose)
microfibrils form - bundles of cellulose chains
Define glycoproteins
proteins that have one or more carbohydrates attached to them
Function of glycoproteins (4)
Cell-cell recognition
act as receptors on surface of cells
can act as ligands
structural support of cells + tissue
Role of glycoproteins in cell to cell recognition (2)
acts as markers on the surface of cells so they can be identified
e.g immune cells attack foreign cells with different glycoproteins
Role of glycoproteins as receptors (3)
act as receptors on cell surfaces
receive signals from other cells or molecules
e.g insulin binds to glycoproteins on surface of body cells
Role of glycoproteins as ligands
ligands - molecules that bind to receptors to initiate a biological response
Glycoprotein role in ABO blood groups (2)
red blood cells have glycoproteins : oligosaccharides called O, A, B
blood with glycoprotein A/B will be rejected by a person who does not produce it
What blood type does not cause rejection problems and why (2)
O
has same structure as A and B but with one monosaccharide less
Features of lipids (3)
hydrophobic + insoluble in water - non-polar
dissolve in non-polar solvents - non-polar solvents have similar polarity to lipids
contains carbon, hydrogen, oxygen
Name of solid lipids at room temperature
fats
Define a tryglyceride (4)
non-polar macromolecule + most common type of lipid
formed from one molecule of glycerol + 3 fatty acids
glycerol stays the same but there are different fatty acids
fatty acids = carboxyl groups (COOH) with a hydrocarbon tail
Name of bond formed between glycerol and fatty acid
ester bond
Define a phospholipid
glycerol molecule with a phosphate group and 2 fatty acids
phosphate head is hydrophilic when fatty acids are hydrophobic
Define saturated fatty acids (3)
straight shape due to no double bonds between carbon atoms
carbon atom in hydrocarbon bonds to 4 atoms
fatty acids can pack together, forming solid at room temp.
Define unsaturated fatty acids (3)
hydrocarbons have one or more double bonds
causes bends in shape
liquid at room temp. - bends make it difficult for molecules to pack together
Types of unsaturated fatty acids (2)
monounsaturated
polyunsaturated
Define monounsaturated fatty acids (3)
have one double bond in hydrocarbon chain
causes a bend in the chain
liquid state at room temp. - bends make it difficult for molecules to pack together
Unsaturated fatty acids vs saturated fatty acids (melting point)
U have lower melting points than S - more double bonds = lower melting point
Why doe unsaturated fatty acids have lower melting points (2)
double bonds disrupt packing of fatty acid molecules
makes them easier to break apart
Terms used to describe different arrangement of unsaturated fatty acids (2)
cis
trans
Define cis unsaturated fatty acids (2)
hydrogen atoms attached to carbon atoms around double bond are on same side
creates bend
Define trans unsaturated fatty acids (2)
hydrogen atoms attached to carbon atoms around double bond are on different sides
linear shape + less flexible than cis
Trans fats vs cis fats (2)
cis occurs in nature, trans produced artificially
cis has lower melting points than trans
Tryglycerides function/characteristics (4)
energy storage - chemically stable so energy not lost
used as insulators to retain heat
liquid at body temperature - can act as shock absorbers
release twice as much energy per gram in respiration than carbs
Define a phospholipid bilayer (4)
double layer of phospholipids
phospholipid bilayers can form when phospholipids are placed in water
hydrophobic fatty acids will orient towards each other
hydrophilic phosphate + glycerol will orient towards water
Features of steroids (4)
lipids
hydrophobic - as they are mainly hydrocarbons
have 4 carbon rings
able to pass through phospholipid bilayer
Functions of steroids (2)
provide phospholipid bilayer with stability + flexibility
role in signalling
Describe the structure of an amino acid (5)
amino group NH2 (basic)
carboxyl group COOH (acidic)
hydrogen atom
central alpha carbon atom
side chains called R groups
Features of the R-group in amino acids (2)
R-groups vary + make amino acids different from each other
affects the way the amino acid bonds with another amino acid
How do amino acids link with one another (2)
carboxyl group reacts with amino group
condensation reaction - bond formed between C and N + H2O produced as by-product
Define essential amino acids (2)
amino acids which the body cannot produced + must be obtained from diet
9/20
Define non-essential amino acids (2)
amino acids which can be produced by the body
11/20
Why does pH cause protein denaturation (3)
high pH = excess H+ can make it difficult to form hydrogen bonds + affecting electronegativity
low pH = lack of H+ reduce number of hydrogen bonds
denaturation = will alter protein shape
Different types of R-groups (3)
charged R-groups which form ionic bonds
R-groups with sulphur atoms that form disulphide bridges
hydrophilic + hydrophobic - some are polar or charged
Describe the primary structure of proteins (3)
sequence of amino acids
peptide bonds between carboxyl + amine group
determines shape of protein - sequence determines how polypeptide chain will fold
Describe the secondary structure of proteins (2)
the folding patterns that occur within the polypeptide chain
hydrogen bonds between O and H atoms on adjacent amino acids form structure
Name 2 types of secondary structure (2)
alpha helix
beta pleated sheet
Features of alpha-helix secondary structure (2)
polypeptide chain forms helical shape
hydrogen bond forms between amine hydrogen of one amino acid + carboxyl oxygen of another 4 residues away
Features of beta-pleated sheet secondary structure (2)
hydrogen bonds form between polypeptide chains parallel to each other
form pleated sheet shape due to tetrahedral bond angles
Define the tertiary structure of proteins (2)
folding of the polypeptide chain into a 3-dimensional structure
stabilized by interactions between R-groups of amino acids
Describe tertiary structure hydrogen bonds between R-groups
hydrogen bonds form between slightly positive hydrogen and slightly negative O or N
Describe tertiary structure ionic bonds between R-groups (4)
ionic bonds between positive + negatively charged R-groups
R-group binding with hydrogen ion = positively charged
R-group losing a hydrogen ion = negatively charged
ionic bonds are more sensitive to pH due to involvement of H+
Describe tertiary structure disulphide bonds between R-groups (3)
disulphide bond between amino acids with sulphur atoms
e.g cysteine and methionine
strongest covalent bonds
Describe tertiary structure hydrophobic interactions between R-groups (3)
water forms hydrogen bonds between polar/hydrophilic amino acids
non-polar amino acids will clump in hydrophobic clusters in the interior of the protein
to minimise contact with surround ing water molecules
Effect of R-group hydrophilic polarity on tertiary structure (2)
R-groups will orient outwards towards water
soluble in water = can allow them to carry out functions in aqueous solution
Effect of R-group hydrophobic polarity on tertiary structure (2)
R-groups reside in protein interior
stabilises protein - maximises hydrophobic interactions within centre + hydrogen bonding between amino acids on surface + water
Define quaternary structure proteins
arrangement of 2 or more polypeptide chains to form a protein
Define non-conjugated proteins (2)
proteins with only polypeptide subunits
e.g collagen + insulin
Define conjugated proteins (2)
proteins with polypeptide subunits + non-protein (prosthetic group
e.g haemoglobin containing haem to bind to oxygen
What happens after a polypeptide chain is synthesised (2)
protein folding - adopts specific 3D shape which corresponds to its function
influenced by sequence of amino acids, hydrogen + ionic bonding, hydrophobic interactions
Name the types of quaternary structure proteins (2)
Globular
Fibrous
Define globular proteins (4)
spherical shaped proteins with irregular folds
soluble in water
play roles as enzymes, transporters, regulators
e.g insulin, haemoglobin, enzymes
Features of insulin as a globular protein (4)
has 2 polypeptide chains - alpha and beta
held in 3D shape by hydrogen bonds, hydrophobic interactions, disulphide bonds
has hydrophilic exterior - allows insulin to react with water + other hydrophilic molecules in blood, able to travel through blood + bind to its receptors
has hydrophobic interior - stabilises globular shape, allows insulin to bind to receptor
Function of insulin (2)
regulates amount of glucose in bloodstream in response to high glucose levels
binds to receptors on cells - allows glucose to enter cells to be used or stored
Define a fibrous protein (3)
elongated polypeptides - polypetide chains linked together into narrow fibres with hydrogen bonds between them
insoluble in water
designed for strength + stability
Collagen as a fibrous protein (2)
3 polypeptide chains twisted together in a triple helix shape
held together by hydrogen bonds
Collagen function
provides structural support to tissues + maintains their shape
How structure of mitochondria relates to its function (4)
cristae increases surface area
matrix - space between 2 membranes
matrix contains enzymes for respiration
small space of matrix allows for high concentration gradients to form
Function of NAD in respiration (2)
functions as coenzyme
is a hydrogen carrier - able to be reduced + oxidised
Where does glycolysis occur
takes place in cytoplasm
Stage 1 of aerobic respiration (glycolysis) (6)
2 molecules of ATP phosphorylate glucose (6 carbon has phosphate added to it)
lysis - phosphorylated glucose split into 2 3 carbon G3P
each G3P oxidised by losing hydrogen atom
2NAD uses H atoms to produce NADH (reduced NAD)
2 ATP produced from each G3P (2 net)
1 glucose will produce net 2 ATP, 2 NADH, 2 pyruvate molecules
Stage 2 of aerobic respiration (link reaction) (5)
2 pyruvates enter matrix of mitochondria through active transport
pyruvates dehydrogenated + decarboxylated
enzymes remove CO2 + transfer hydrogen to NAD (NADH)
pyruvate bonds with acetyl group (CoA) become 2 acetyl CoA
2 NADH formed + 2CO2 produced as waste product
Stage 3 of aerobic respiration (krebs cycle) (7)
takes place in matrix of mitochondria
acetate from Acetyl CoA (2C) binds with oxaloacetate (4C) to make citrate (6C)
Co-A goes back to link reaction
oxidative decarboxylation - CO2 molecule removed + NAD becomes NADH + citrate becomes 5-carbon compound
2nd oxidative decarboxylation - another CO2 molecule removed + NAD becomes NADH + one molecule of ATP formed + 4-carbon compound
2H used to reduce FAD + H2O added to 4-carbon compound + NAD reduced again to make oxaloacetate
per glucose 6 reduced NAD, 2 reduced FAD, 2 ATP, 4 molecules of CO2
Glycolysis for Anaerobic respiration in animal cells (lactic acid fermentation) (2)
NADH becomes NAD+
Pyruvate forms lactate/lactic acid + carbon dioxide
Factors which determine how much ATP can be generated (4)
availability of hydrogen when respiratory substrates are broken down
more hydrogen = more reduced NAD
more reduced NAD = more protons to be transported across IMM
more ATP generated
No. of ATP generated by lipids (2)
460 ATP
produce more due to having long chains of carbon + hydrogen
Why Lipids are not used as a main respiratory substrate (4)
lipids must first be broken down to glycerol + fatty acids
glycerol must be further broken down to be used in glycolysis
fatty acids must be broken down into acetyl groups
lipids are harder to digest + transport (hydrophobic)
Why proteins are not used as main respiratory substrate
produce toxic nitrogenous wastes (NH3)
Inner Mitochondrial Membrane (IMM) (2)
membrane of matrix of mitochondria
contains series of 4 transmembrane proteins + 2 electron carriers
Explain the electron transport chain (6)
reduced NAD (NADH) delivered to protein I
NADH –> NAD+, H+, 2e-
2 electrons passed along electron carriers
electrons allow H+ ions to be pumped into intermembrane space
FAD delivers electrons to 2nd protein
proton (H+) gradient created between intermembrane space + matrix
Role of oxygen in electron transport chain (3)
electrons must go somewhere
O2 split into individual oxygen atoms
each O2 molecules joins with 4e- + 4H+ to form 2 H2O molecules
Define an enzyme (3)
biological catalysts
speed up chemical reactions + increase rate of occurrence
globular proteins
Define metabolism
complex network of interacting chemical reactions in living organisms
Significance of enzyme shape to being complementary to subtrate (2)
interactions of amino acids determine active site shape
active site created from folding of polypeptide chain
How enzymes catalyse reactions (6)
substrate moves randomly until close enough to active site
chemical properties of enzyme surface attract substrate to active site
induced fit-binding : interactions between substrate + AS change 3D shape of both
if 2nd substrate, it will bind to another part of AS
changed substrate molecules weaken bonds + allow new bonds to form to make products
products detach from A.S + enzyme activity site returns to original shape
Variation of molecular motion between enzymes and substrates (3)
most cases substrate smaller than enzymes = substrate moves more
some substrates large + dont move much = enzyme has to move in relation to substrate
some enzymes embedded in membranes = substrate does all movement
Why pH affects enzyme activity (2)
prescence/abscence of hydrogen ions affects ionic bonds between amino acids
changes AS shape
Define extracellular enzymes (2)
enzymes released from cell + work outside it
synthesized by ribosomes attached to endoplasmic reticulum
Define intracellular enzymes (2)
enzymes used within cells
synthesized by ribosomes in cytoplasm
Define an allosteric site
second active site for a different substance to bind/unbind to
Features of non-competitive inhibitors (4)
bind to allosteric site - change shape of enzyme
enzyme rate of reaction decreases
changing enzyme shape = A.S no longer complementary to substrate
hence fewer complementary enzymes
Features of competitive enzyme inhibitors (4)
bind to active site of enzyme = substrate cannot bind to A.S
chemically similar to substrate
inhibitor competes with substrate for A.S
faster rate of reaction than non-competitive inhibitor
Features of end-product inhibition (2)
enzymes allosterically inhibited by end-product of pathway
prevents over-production of certain substance
Features of mechanism-based inhibition (3)
irreversible binding of inhibitor to A.S through covalent bond
enzyme permanently loses catalytic ability
harmful to organisms
Properties of ATP (5)
soluble in water - can move freely through cytoplasm
stable at pH levels close to neutral
cannot pass freely through phospholipid bilayer
3rd ATP phosphate group easily removed + attached through hydrolysis + condensation reaction
hydrolysing ATP to ADP + phosphate releases energy
Define a coenzyme
molecule required for enzyme to carry out a function
Reduced NAD equation (3)
NAD+ + 2H+ + 2e- –> NADH + H+ (reduced NAD)
NAD initially has one positive charge
NAD accepts 2 e + 1 p from 2 hydrogen atoms
Glycolysis for anaerobic respiration in yeast (ethanol fermentation) (2)
pyruvate converted to ethanol
CO2 produced + NADH oxidised to NAD (H used to make ethanol)
ATP synthase role in ATP generation
flow of protons (proton motive force) generates energy to phosphorylate ADP
H+ ions pass through ATP synthase through diffusion –> rotates + converts ADP to ATP
Define chemiosmosis
flow of protons (H+) down electrochemical gradient to generate energy
Define photosynthesis
production of carbon compounds in cells using light energy
Why leaves are green (2)
chlorophyll a + b absorbs other lights more + reflects green light most
pigments are bad absorbers of green light
Photosynthesis light-dependent stage (4)
photons of light hit pigments inside photosystems
excite electrons within the molecules
excited electrons transferred to reaction centre
photoactivation - photochemical reaction occurs which emits excited electron
Photosynthesis light-independent stage (Calvin cycle) (2)
takes place in stroma
uses ATP + reduced NAD to form carbon compounds (glucose) from CO2
Electron transport chain of non-cyclic photophosphorylation (5)
electrons released from PSII passed along electron carriers onto PSI
electrons re-excited by light energy from PSI
electrons passed onto protein ferrodoxin
electrons from ferrodoxin react with H+ in stroma to form H atoms
NADP –> reduced NADP (NADPH) (accepts 2 electrons from PSI + 2 H+ from stroma)
Cyclic photophosphorylation (3)
light energy causes excitation of electrons from PSI
electrons move to electron carriers to pump H+ across
electrons will return to same PS1 after moving along carriers
Carbon fixation stage of Light independent stage of photosynthesis (Calvin Cycle) (2)
Co2 added to RuBP (5C) - catalysed by rubisco
forms 2 molecules of GP3 (3C)
Define rubisco
enzyme which adds CO2 to RuBP
Reduction of GP stage of Calvin cycle (2)
one ATP molecule adds phosphate to GP
hydrogen added to GP from NADPH to become triose phosphate
Regeneration of RuBP (4)
6 CO2 can make 12 triose phosphate
10 triose phosphate (30C) used to make 6 RuBP (5C each)
requires 1 ATP
2 triose phosphate left over can synthesize carbon compounds
Uses of excess triose phosphate produced (4)
glucose/starch
amino acids
fatty acids
DNA/RNA
Define photolysis
reaction which splits molecules of water using light energy
Different pigments of a leaf (3)
chlorophyll
beta-carotene
xanthophyll
Define an action spectrum (2)
graph comparing rate of photosynthesis with wavelength of light
shows which wavelengths are good for photosynthesis
How can CO2 concentration be controlled in photosynthesis experiments
dissolving sodium hydrogen carbonate in water
How can photosynthesis be measured (4)
hydrogen carbonate indicator solution
change colour as CO2 concentration changes
less photosynthesis, more respiration = CO2 will increase + indicator turns orange/yellow
more photosynthesis, less respiraton = CO2 will decrease + indicator turns purple
Define photosystems (3)
molecular arrays of chlorophyll + accessory pigments
within protein complexes + located in membranes
capture light energy + convert to chemical energy
Penicillin as mechanism-based inhibition (3)
bacterial cell wall protects + prevents bacteria from bursting
transpeptidase - enzyme which maintains cell wall structure by forming cross-links with polysaccharide chains
penicillin binds to transpeptidase irreversibly - inhibits its function + cell wall weakens
Photosystems in thykaloid membranes (2)
photosystem I - most sensitive to light wavelengths of 700nm
photosystem II - most sensitive to light wavelengths of 680nm
Advantages of photosystems having different pigments in a structured array (2)
variety of pigments = enough light energy for light dependent stage
energy only transferred from one close pigment to another - structure allows energy to reach reaction centre
How oxygen is created from light independent stage of photosynthesis (5)
release of electrons from reaction centre creates unstable oxidised molecule
water molecules split to give up electron –>1/2 O2 + 2H+ + e-
electron replaces electron lost in reaction centre
protons released to thykaloid space to increase proton electrochemical gradient
oxygen diffuses out
ATP generation in photosytems II (2)
hydrogen ions accumulate in intermembrane space
H+ diffuse through ATP synthase to phosphorylate ADP to ATP
Features of Thykaloids (2)
flattened membrane-bound sacs
contain photosystems
Features of grana (2)
stacks of thykaloids
provide SA for as much photosystems, ETCs as possible
Features of lamella
connects grana to each other
Features of stroma lamella (2)
unstacked thykaloids
form connections between thykaloids in grana
Why is there a high concentration of Rubisco (2)
inefficient - slow enzyme + high energy requirements
can be competitively inhibited by oxygen
Interdependence of light dependent + light independent (Calvin cycle) (2)
Calvin cycle requires ATP + reduced NADP from light dependent
light dependent requires NADP + ADP to produce ATP + reduced NADP
Directionality of transcription
3’ to 5’
Features of tRNA (transfer RNA) in translation (4)
translates base sequence of mRNA in to amino acid sequence
tRNA has anticodon at one end + attachment point at other end for amino acid corresponding to anticodon
transfers corresponding amino acid to end of growing polypeptide once code on mRNA recognised
tRNA has specific corresponding amino acid attached
Shape of tRNA (3)
single-stranded RNA molecule
folds on itself to form clover-leaf structure
with double stranded regions + 3 hairpin loops
Features of ribosomes in translation (4)
acts as enzyme to form peptide bonds between amino acids
complex structure of small + large subunit
small subunit binds to mRNA
large subunit has 3 binding sites for tRNA
Define an anticodon
3-base code complementary to the matching RNA codon
Stages of translation (3)
initiation
elongation
termination
Elongation stage of translation (5)
ribosome moves along mRNA, one codon at a time
as each codon moves into place, new tRNA carries corresponding amino acid,
attaches + moves previous tRNA molecules to the next position
new amino acids are delivered = condensation reactions catalysed + peptide bonds formed
repeats until termination codon reached
Directionality of translation
5’ to 3’ direction
Define a promoter (3)
section of DNA that initiates gene transcription
proteins known as transcription factors bind to promotor-
act as binding point for RNA polymerase enzymes that catalyse transcription
Importance of transcription factors (2)
binding of correct transcription factors –> allows the RNA polymerase to also bind + begin to transcribe the DNA into RNA.
transcription factors are missing or cannot bind to the promoter = transcription will not take place and that gene cannot be expressed
Features of non-coding genome (3)
98% of the human genome
DNA sequences within genome that do not have information to make protein.
not represented within the amino acid sequence of expressed proteins.
Regions of non-coding DNA (4)
regulators of gene expression
introns
telomeres
genes for tRNA + rRNA
Define regulators of gene expression (4)
promoters
DNA sequences that are binding sites for proteins e.g enhancers + silencers
enhancers - increase rate of transcription
silencers - decrease rate of transcription
Define introns
DNA base sequences in eukaryotic genes that are removed at end of transcription
Define telomeres (3)
repetitive sequences that protect ends of chromosome.
ensure that DNA is replicated correctly
every cell division = telomeres lose short stretches of DNA
Features of post-transcriptional modification (3)
mRNA must be prepared for translation
genes contain non-coding information –> must be removed
only for eukaryotes
Procedure of post-transcriptional modification (5)
transcription - synthesis of pre-mRNA
addition of a 5’ cap + poly-A tail - protect the mRNA molecule from degradation by stabilising ends
5’ cap = modified nucleotide added to 5’ end of RNA
poly-A tail - 100-200 adenine molecules added to 3’ of RNA
splicing - removes (excises) introns and joins (ligates) exons to form mature mRNA.
Define alternative splicing (2)
gene can be spliced in multiple ways by combining different exons and omitting others
creates different versions of proteins with different functions
Define initiation stage of translation (6)
Translation starts - 5’ terminal of mature mRNA binds to small ribosomal subunit at mRNA binding site
all mRNA have start codon (AUG) which can be linked to the initiator tRNA
This specific tRNA always carries methionine - all proteins start with this amino acid
ribosome moves along mRNA until it finds the start codon
anticodon of the initiator tRNA (amino acid methionine) binds to codon of the mRNA
large ribosomal subunit joins
Features of post-translational modification (3)
polypeptides synthesised by ribosomes on the rough endoplasmic reticulum are packaged in vesicles
vesicles carry polypeptides to the Golgi apparatus.
modifications carried out in Golgi apparatus
Recycling of amino acids by proteasomes
unneeded/damaged proteins can be broken down + recycled for amino acids
carried out by proteasome (protein complex)
hydrolyses proteins by breaking the peptide bonds between amino acids
Function of recycling amino acids by proteasomes (3)
proteome = total proteins made within body
production of proteins + large supply of amino acids needed to maintain proteomes
provides amino acids to do this
PCR + gel electrophoresis use in DNA profiling (5)
tandem repeats - short repeated DNA sequences
restriction enzymes chop DNA into fragments (lengths based on number of repeats)
PCR amplifies DNA fragments
DNA fragments then separated using gel electrophoresis
match = same number + length of DNA fragments
How are DNA nucleotides held together (2)
phosphodiester bond
bond between phosphate group of 5’ carbon deoxyribose and hydroxyl group of 3’ carbon deoxyribose on next nucleotide
Define a phosphodiester bond
occurs when 2 hydroxyl groups in phosphoric acid react with groups in other molecules to form 2 ester bonds
Directionality of DNA polymerase
5’ carbon to 3’ carbon
Define the DNA leading strand (3)
strand that can be replicated in same direction as helicase (5’ to 3’)
strand has 3’ to 5’ directionality
can be replicated continously (completed quicker)
Define the DNA lagging strand (2)
strand that cannot allow DNA polymerase III to move in 5’ to 3’ directionality
strand has 5’ to 3’ directionality
DNA strand replication for lagging strand (3)
DNA polymerase III adds nucleotides away from fork movement (opposite to leading)
nucleotides added in sections as replication fork exposes more of template
sections called Okazaki fragments
Function of Helicase enzyme in DNA (2)
unwinds DNA molecule by breaking hydrogen bonds between bases
single strand binding proteins attach to single strand of DNA + prevent them from re-forming hydrogen bonds with comp. bases
Function of gyrase enzyme in DNA (2)
moves ahead of helicase
relieving tension created by unwinding DNA
Function of DNA primase (2)
attaches small RNA primers (RNA nucleotides) to template strand
allows DNA polymerase III to attach to DNA strand
Function of DNA polymerase III (2)
places free nucleotides complementary to bases in template strand
only builds new strands in 5’ to 3’ directionality
Function of DNA polymerase I
removes RNA nucleotides of primers + replaces with correct DNA nucleotide
Function of DNA ligase
catalyses formation of phosphodiester bonds between Okazaki fragments
DNA polymerase III in proofreading (2)
proofreads newly formed DNA strand while it is built
nucleotide paired with mismatched base = incorrect nucleotide replaced with correct
Impacts of frameshift mutations (3)
alters amino acid sequence coded by DNA sequence
addition of new nucleotides alters grouping of codons
mRNA transcript produced will have different codon structures
Examples of chemical mutagens (3)
mustard gas
nitrous acid
Formaldehyde
Example of physical agent mutagens (3)
UV Radiation
X-Ray
Gamma rays
Impact of radiation on gene structure (3)
single-strand breaks - interrupts continuity of template strand –> replication errors
double strand breaks
chemical alterations to bases
Base with highest probability of mutation (3)
cytosine
can experience chemical reaction called deamination
can lose an amine group –> becomes uracil
Factors that influence mutation rate (3)
exposure to mutagens
DNA repair mechanisms
fidelity of DNA replication - accuracy of DNA copy
Mutations in somatic cells (2)
can cause diseases in person’s lifetime (e.g cancer)
not passed onto offspring
Mutations in germ cells (2)
passed onto offspring - mutations inherited by offspring
can cause genetic disorders, change chromosome number, increase susceptibility to certain disease
Define neutral/silent mutations (3)
mutations which do not significantly affect organism
neutral mutations - occur in non-coding regions of genome + regions that do not alter function of essential genes
silent mutations - occur in coding regions but do not alter amino acid sequence due to degeneracy
Define harmful mutations (2)
mutations that cause negative consequences for organism
can cause disease, abnormality, reduce organisms survival
Define beneficial mutations (2)
mutations that are advantageous to organism
improve ability to adapt, reproductive success, resistance to disease
Define genetic engineering (2)
process of altering DNA of organisms
to introduce new characteristics, modify characterstics, remove undesired characteristics
Define gene knockout technique (2)
specific gene is intentionally removed/changed to prevent its expression
helps to discover function of specific gene
Gene knockout technique in mice (4)
prepared DNA inserted into genome of embryotic mouse cells –> replaces + deletes target gene
succesful procedures grown into adult mice
males + females with only one copy mated - 25% expected to have no copies of target gene (knockout mice)
phenotype of knockout mice investigated to find out traits changed
Components of CRISPR-Cas 9 (2)
enzyme Cas9 - cuts DNA at specific target sites on chromosome
CRISPR
Define CRISPR (2)
short repeated base sequences
unique spacer sequences
Define the CRISPR Cas-9 system for bacteria (3)
used by bacteria against invading foreign DNA (viruses)
incorporate short segments of foreign DNA into their own genome
bacteria create molecular record of previous infections
Explain the CRISPR Cas-9 procedure for bacteria (4)
foreign DNA matches
foreign DNA matches CRISPR spacer –> corresponding RNA identifies + binds to specific viral sequences
guides Cas9 to target DNA to make precise cuts in DNA
causes double stranded break that can be repaired by cell’s DNA repair mechanism
CRISPR Cas-9 in gene editing (4)
creating single guide RNAs (sgRNA) to target specific genes for modification or deletion
sgRNA molecule specifically targets + bind to a particular DNA sequence of interest
guides Cas9 enzyme to location and enables it to make precise cuts in the DNA, resulting in double-strand break.
scientists can add, delete or modify the DNA sequences at that point
Application of CRISPR Cas-9 system (4)
gene therapy
agriculture
disease modelling
genetic engineering of microorganisms
Gene therapy in CRISPR Cas-9 system (3)
treats genetic disorders
correcting disease-causing mutations in a patient’s cells
e.g sickle cell anaemia.
Agriculture in CRISPR Cas-9 system (3)
ability to transform crop breeding practices
introducing precise genetic modifications to enhance desirable traits
improve crop yield + nutritional content and disease resistance
Disease modelling in CRISPR Cas-9 system (3)
creates animal models to simulate human diseases
introduces mutations or deleting genes in animals
researchers gain info into disease progression + potential treatment
Genetic engineering of microorganisms (3)
make modifications to genetic material of bacteria, yeast or other microorganisms.
enhance microorganisms’ ability to produce valuable compounds such as pharmaceuticals, biofuels and enzymes.
creation of efficient microbial factories to contribute to sustainable production
Define conserved sequences
sequences remain identical or similar across species or group of species
Define highly conserved sequences
sequences that remain similar over long periods of evolution
Role of conserved and highly conserved sequences (2)
provide clues about function/importance sequences for evolution of species
functional constraints - selective pressures prevent mutations in these genes as they are vital for life
