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A-Level Biology > Unit 1 - Biological Molecules > Flashcards

Unit 1 - Biological Molecules Flashcards

1
Q

define monomers

A

smaller units from which larger molecules are made

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2
Q

define polymers

A

large, complex molecules made from joining long chains of many monomers together

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3
Q

give 3 examples of monomers

A

monosaccharides
amino acids
nucleotides

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4
Q

define condensation reaction

A

two molecules join together with the formation of a chemical bond and a water molecule is released

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5
Q

define hydrolysis reaction

A

breaks (hydrolyses) a chemical bond between two molecules using a water molecule to form monomers

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6
Q

what are the properties of water & why are they important?

A
  1. a metabolite in many metabolic reactions including condensation & hydrolysis
  2. an important solvent in which metabolic reactions occur
    water readily dissolves O2, CO2, ammonia, urea & enzymes
  3. has high specific heat capacity, which buffers changes in temperature
    organisms are mostly H2O so maintains constant body temperature
  4. has a large latent heat of vaporisation, providing a cooling effect with little water loss through evaporation - evaporation of sweat (mostly H2O) in mammals (thermoregulation)
  5. has strong cohesion between water molecules
    supports columns of water in xylem of plants (transpiration stream)
    provides surface tension where water meets air - vital for supporting small organisms e.g. pondskaters
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7
Q

define monosaccharides & what are the common monosaccharides?

A

the monomers from which larger carbohydrates are made
e.g. glucose, galactose, fructose

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8
Q

how is a glycosidic bond formed?

A

in a condensation reaction between two monosaccharides
a water molecule is released
a glycosidic bond is a type of covalent bond

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9
Q

what happens in a hydrolysis reaction involving a disaccharide?

A

a water molecule is added to the disaccharide to hydrolyse the glycosidic bond

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10
Q

how is a disaccharide formed?

A

condensation of two monosaccharides

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11
Q

how are maltose, sucrose & lactose formed?

A

maltose is formed by condensation of two alpha glucose molecules
sucrose is formed by condensation of a glucose molecule & a fructose molecule
lactose is formed by condensation of a glucose molecule & a galactose molecule

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12
Q

define isomers

A

molecules with the same molecular formula but different structural formula

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13
Q

what are the isomers of glucose?

A

alpha glucose - hydroxyl group is below the plane of the ring on carbon-1

beta glucose - hydroxyl group is above the plane of the ring on carbon-1

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14
Q

what is the name for a sugar with 5 carbon atoms & with 6 carbon atoms?

A

5 - pentose
6 - hexose

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15
Q

how are polysaccharides formed?

A

many monosaccharides are joined together by glycosidic bonds in a condensation reaction

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16
Q

what are the structures & functions of starch?

A

polymer of alpha glucose that is the store of glucose (energy) in plants
1. spiral/helical shape
compact, lots of glucose can be stored in a small volume

  1. large & insoluble
    cannot leave the cell
    does not affect the water potential/osmosis
  2. can be branched
    several ends, each end can release glucose by hydrolysis for respiration/transport when needed
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17
Q

what are the structures & functions of glycogen?

A

polymer of alpha glucose that is the store of glucose in animals/bacteria
similar to starch but shorter chains & more branching
1. highly branched (more than starch)
more ends so faster hydrolysis so more alpha glucose released because animals have a higher metabolic rate than plants

  1. large & insoluble
    cannot leave the cell
    does not affect the water potential/osmosis
  2. helical shape
    compact - lots of glucose stored in a small volume
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18
Q

what is the structure & function of cellulose?

A

plant cell wall (structural support)
polymer of beta glucose, which causes straight, unbranched chains
each cellulose polymer can form hydrogen bonds with a different parallel polymer because of the polar hydroxyl groups
(hydrogen bonds are individually weak but collectively strong)
cellulose molecules are bundled into microfibrils which are grouped into fibres
this causes the cell wall to be rigid & prevents the cell bursting so it stays turgid

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19
Q

what is the test for starch?

A

iodine test
add 2 drops of iodine solution (iodine dissolved in potassium iodide solution) & shake
positive result is a colour change from orange-brown to blue-black

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20
Q

what is the test for reducing sugars?

A

benedict’s test
add 2cm3 of benedict’s reagent (an alkaline solution of copper (II) sulphate)
heat in water bath at 80 degrees/boiling for 5 minutes
positive result is a brick red, orange, yellow or green precipitate forms according to the concentration of the reducing sugar (brick red shows highest concentration)

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21
Q

what is the test for non-reducing sugars?

A

hydrolysis then benedict’s test
add 2cm3 of dilute hydrochloric acid to sample
boil in a gently boiling water bath for 5 minutes to hydrolyse the glycosidic bonds between the monosaccharides
neutralise the solution by slowly adding sodium hydrogen carbonate solution (test with pH paper to check the solution is alkaline)

add 2cm3 of benedict’s reagent (an alkaline solution of copper (II) sulphate)
heat in water bath at 80 degrees/boiling for 5 minutes
positive result is a brick red, orange, yellow or green precipitate forms according to the concentration of the reducing sugar (brick red shows highest concentration)

negative result for benedict’s test before hydrolysis then a positive result after hydrolysis

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22
Q

what is the test for lipids?

A

emulsion test
add 5cm3 ethanol & shake thoroughly to dissolve the lipid
add 5cm3 distilled water & shake gently
positive result is a colour change from colourless to white cloudy emulsion

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23
Q

what is the test for proteins?

A

biuret test
add 2cm3 biuret reagent
positive test is colour change from colourless to lilac

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24
Q

what are 2 groups of lipid?

A

triglycerides
phospholipids

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25
Q

how is a triglyceride formed?

A

condensation of one molecule of glycerol & 3 molecules of fatty acid
ester bonds formed between 1glycerol & 1 fatty acid molecule
3 molecules of water formed

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26
Q

what is an ester bond?

A

covalent bond joining 1 fatty acid to a glycerol

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27
Q

what are the functions of triglycerides?

A

effective energy reserve: insoluble (form droplets w hydrophobic tails on inside) so no impact on osmosis
triglycerides can be oxidised
releases more energy than carbs

insulation:
slow conductor of heat & electrical insulators (e.g. myelin sheath)

protection: e.g. around kidneys

metabolic source of water: when oxidised release water

waterproofing: plants & insects have waxy cuticle

buoyancy in aquatic animals: lipids are less dense than water

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28
Q

what is the structure of a phospholipid?

A

hydrophilic phosphate ion - polar head group
1 molecule of glycerol
2 hydrophobic fatty acid tails

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29
Q

what is the function of a phospholipid?

A

form bilayer = main component of plasma membranes where they contribute to:
flexibility
allow lipid-soluble substances to pass through membranes e.g. O2 & CO2

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30
Q

what is the structure of a glycolipid?

A

short carbohydrate chain
1 molecule of glycerol
2 fatty acid tails

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31
Q

what is the function of a glycolipid?

A

located in cell membranes:
stabilisers - carbohydrate chain form h bonds with water

antigens - molecule recognised as foreign by lymphocytes

receptors - able to interact w specific molecules e.g. hormone

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32
Q

what is the function of cholesterol?

A

located in cell membranes - regulates flexibility
converted into steroid hormones & vitamin D

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33
Q

what is the structure of fatty acids?

A

all have a carboxyl group
r groups: varying lengths of hydrocarbon chain attached
hydrocarbon chain can be saturated or unsaturated

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34
Q

what is the difference b/w saturated & unsaturated fatty acids?

A

saturated: no c=c
unsaturated: at least one c=c

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35
Q

what is the difference b/w monounsaturated & polyunsaturated fatty acids?

A

mono: one c=c
poly: more than 1 c=c

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36
Q

structure of saturated & unsaturated fatty acids?

A

saturated: no kink
unsaturated: kink
c=c causes molecule to kink so they cannot pack together tightly so liquid at room temp.

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37
Q

what is the monomer of proteins?

A

amino acids

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38
Q

what is a dipeptide?

A

formed when 2 amino acids are joined together by 1 peptide bond

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39
Q

what is a polypeptide?

A

polymer made up of more than 2 amino acids

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40
Q

how are polypeptides formed?

A

in condensation reactions, amino acids are joined together by (covalent) peptide bonds
molecule of water released per peptide bond

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41
Q

what is a protein?

A

a polypeptide that has a function

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42
Q

what is the general structure of amino acids?

A

see spec.

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43
Q

what are examples of proteins in the human body?

A

enzymes
muscles
antibodies
collagen
haemoglobin

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44
Q

what is the structure of an amino acid?

A

central carbon bonded to hydrogen atom
carboxyl group
amine group
r group

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45
Q

there are 20 different amino acids

A

each amino acid has a different r group

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46
Q

why are amino acids polar?

A

polar amine group
polar carboxyl group

47
Q

describe a peptide bond

A

forms in condensation reaction b/w 2 amino acids to form a dipeptide
1 water molecule removed by combining -oh from carboxyl group of 1 amino acid & -h from amine group of another amino acid
broken in hydrolysis reaction by adding water
both catalysed by enzymes

48
Q

what is the primary structure?

A

the specific sequence & number of amino acids in a polypeptide
determined by the order of bases in a gene (DNA)

1 structure determines the type & position of bonds in the protein - so function & 3 structure depend on 1 structure

49
Q

what is the secondary structure?

A

hydrogen bonds pull polypeptide chains into regular patterns e.g. alpha helix (coiling) (& beta pleated sheets)
h bonds form b/w -nh group of 1 aa & -c=o group of another

50
Q

what is the tertiary structure?

A

specific 3d structure
polypeptide chain is coiled & folded
due to interactions b/w r groups
function depends on 3 structure

51
Q

what 2 changes disrupt tertiary structure & denature the enzyme/protein?

A

changes in pH
high temperature

52
Q

what are the 3 bonds in tertiary structure?

A
  1. hydrogen bonds b/w polar r groups
  2. ionic bonds b/w 2 ionised r groups
  3. disulfide bonds (covalent & very strong) b/w 2 cysteine r groups
53
Q

how are the 3 bonds broken?

A

h bonds - weak, broken by high temp. & pH change

ionic bonds - only broken by pH change

disulfide bonds - covalent & very strong so not easily broken

54
Q

what is the tertiary structure impacted by?

A

primary structure

55
Q

what is the quaternary structure?

A

2 or more polypeptides held together to make a functioning protein
e.g. haemoglobin, antibodies, collagen

56
Q

what are fibrous vs globular proteins?

A

fibrous:
stands/fibres
insoluble in water
e.g. collagen in tendons, keratin in hair

globular:
coiled/folded into ball shape
soluble in water
e.g. haemoglobin, enzymes, insulin

57
Q

what are the important features of haemoglobin?

A

globular

made up of 4 polypeptides

Fe2+ ion (haem group) is an important ion

contains h-bonds, ionic bonds & disulfide bonds

pigment that carries oxygen

1 O2 molecule can bind to each Fe2+ ion reversibly to produce oxyhaemoglobin (4 O2 molecules can be carried by 1 haemoglobin molecule)

soluble in red blood cell cytoplasm

58
Q

what are the important features of collagen?

A

fibrous

alpha helix due to h-bonds

covalent bonds b/w r groups to form fibrils that form fibres

structural protein e.g. tendons

high tensile strength due to many h-bonds & covalent cross-links

insoluble in water

59
Q

how do amino acids form a chromatogram in water?

A

most polar aa is the most soluble in water so would move the furthest up the chromatography paper

60
Q

what is the function of enzymes?

A

enzymes are biological catalysts
enzymes increase the rate of reaction by providing an alternative reaction pathway of lower activation energy
enzymes can be re-used

61
Q

how do enzymes lower the activation energy?

A
  1. hold substrates closer together so condensation more likely
  2. stretch bonds in substrate so hydrolysis more likely
62
Q

what is the structure of enzymes?

A

active site - specific 3d region (caused by 3 structure/interactions b/w r groups) where substrate can reversibly bind
substrate has complementary shape to active site

63
Q

how is an enzyme-substrate (esc) formed?

A

during reaction, substrate forms temporary interactions e.g. hydrogen bonds with r groups of amino acids in active site
enzyme is specific to its substrate due to specificity of active site (small functional region)

64
Q

summary of enzyme-catalysed reaction

A

enzyme + substrate –> esc –> enzyme + product

65
Q

explain the lock & key model

A
  1. shape of substrate fits the shape of the enzyme active site exactly - specificity of enzymes which catalyse a single reaction
  2. assumes the structure of an enzyme is rigid
    but incorrect:
    binding of other molecules (e.g. inhibitors) altered enzyme activity even when bound away from active site
    so structure of an enzyme is flexible
66
Q

explain the induced fit model

A
  1. the shape of the enzyme’s active site is not exactly complementary to the shape of the substrate
  2. when the substrate is present, the active site changes shape bc 3 structure changes & becomes exactly complementary to substrate
  3. forming an enzyme-substrate complex
  4. the products are formed & the enzyme is unchanged
67
Q

why is the induced fit model better than lock & key model?

A

it explains how activation energy is lowered & explains how other molecules (e.g. non-competitive inhibitors) can alter enzyme activity

68
Q

what are the similarities & differences b/w the lock & key & induced fit models?

A

similarities:
substrate binds to active site
esc formed

differences:
active site changes shape in if, but not in l&k
initially, the active site is not exactly complementary to the substrate in if, but it is in l&k

69
Q

what factors affect the rate of enzyme-controlled reactions?

A

enzyme concentration
substrate concentration
temperature
pH

70
Q

what does the graph of time & vol. of products for increasing enzyme concentration look like?

A

see booklet

71
Q

what does the graph of increasing enzyme concentration vs initial rate of reaction look like & describe it?

A

see booklet for graph

at the start, enzyme concentration is the limiting factor
as enzyme conc. increases, the # of esc formed per sec increases
so # of products formed per sec increases & initial rate increases

after a certain concentration, substrate concentration is the limiting factor
there are not enough substrate molecules to bind to the extra active sites
(temp. & pH may be limiting if not optimum)

72
Q

what does the graph of time & vol. of products for increasing substrate concentration look like?

A

see booklet
as substrate concentration increases, the total volume of product produced increases

73
Q

what does the graph of increasing substrate concentration vs initial rate of reaction look like & describe it?

A

see booklet for graph

at the start, substrate concentration is the limiting factor
as substrate concentration increases, the # of collisions per sec increases so the # of esc per sec increases
so # of products formed per sec increases & initial rate increases

after a certain concentration, enzyme concentration is the limiting factor
there are not enough active sites available for the extra substrate particles
the active sites are saturated

74
Q

what does the graph of increasing temperature vs initial rate of reaction look like & describe it?

A

see booklet for graph
as temperature increases, kinetic energy of the substrate & enzyme increases so collisions b/w them are more frequent
more esc formed per sec so initial rate increases

after a certain temperature, there is enough ke to break r group interactions (3 structure & 3d shape) e.g. h-bonds
so 3 structure changes so active site shape changes shape so it is no longer complementary to the shape of the substrate
so enzymes denature
so fewer esc formed per sec & rate decreases

75
Q

what does the graph of increasing pH vs initial rate of reaction look like & describe it?

A

see booklet for graph
pH is varied using buffer solutions

each enzyme has a narrow pH range in which it is active
small pH changes can denature the enzyme bc of changes in 3 structure (ionic & h-bonds)
active site shape changes so cannot form esc
so rate decreases

76
Q

what is a limiting factor?

A

a factor present at a low level so it slows/limits the rate

77
Q

what is a competitive inhibitor & explain structure?

A

molecules that bind to the active site of an enzyme to prevent substrate molecules from binding
so inhibitor competes with substrate
so fewer esc

similar shape to substrate molecules

78
Q

what is a non-competitive inhibitor & explain structure?

A

a molecule that binds to the allosteric site of an enzyme, which changes the shape of the active site (3 structure)
so shape of substrate & as no longer complementary so fewer esc

inhibitor has a different structure to substrate

79
Q

what is an example of a process that relies on non-competitive inhibitors?

A

end product inhibition (-ve feedback)
important in regulating a series of reactions

80
Q

what is a competitive inhibitor & give example?

A

drugs that bind @ ac
inhibitor prevents substrate from binding
fewer esc formed per sec
less product made
reduced rate

81
Q

what happens to the rate of reaction as more substrate is added to a solution containing non-competitive inhibitors?

A

the rate of reaction will not be changed
once there is enough substrate to fill active sites

82
Q

what happens to the rate of reaction as more substrate is added to a solution containing competitive inhibitors?

A

increase in substrate concentration
so the rate of reaction will increase
bc competitive inhibitor is overcome

83
Q

what does the graph of substrate conc. vs rate for comp. & non-comp. inhibitors look like?

A

see booklet

84
Q

explain how the active site of an enzyme causes a high rate of reaction?

A

lowers activation energy
induced fit causes active site to change shape
so esc causes bonds to form or break

85
Q

what is the function of RNA?

A

protein synthesis

86
Q

what are the types of RNA?

A

messenger RNA - mRNA
ribosomal RNA - rRNA
transfer RNA - tRNA
microRNA (involved in post-transcriptional gene expression - non-coding)

87
Q

what are the monomers of DNA & RNA & what is the polymer?

A

mononucleotides
polynucleotides

88
Q

what are the similarities b/w DNA & RNA?

A

every DNA/RNA nucleotide has same pentose & phosphate group but bases vary
DNA & RNA have 3 same bases: adenine, cytosine & guanine

89
Q

what are the differences b/w DNA & RNA?

A

pentose sugar in DNA nucleotide is deoxyribose sugar vs ribose sugar in an RNA nucleotide
thymine in DNA vs uracil replaces thymine in RNA
DNA is double stranded vs RNA is single stranded
DNA is longer than RNA

90
Q

describe the structure of DNA

A

polymer of mononucleotides
each mononucleotide is formed from a deoxyribose sugar, phosphate & a nitrogenous base
phosphodiester bonds form b/w nucleotides
it is double-stranded - the antiparallel strands are held together by hydrogen bonds to form a double helix
complementary base pairing b/w adenine & thymine & cytosine & guanine

equal amounts of C&G & A&T

91
Q

describe the H bonds in DNA

A

individually H-bonds b/w complementary bases are weak so DNA can be separated for DNA replication & transcription can happen

92
Q

why is the double strand important?

A

each strand can act as a template in semi-conservative replication, which determines the order of new bases, so the DNA is copied exactly

93
Q

why is complementary base pairing important?

A

allows accurate replication

94
Q

why are free-floating DNA nucleotides important?

A

forms complementary base pairs

95
Q

describe the structure of RNA

A

single polynucleotide chain
shorter than DNA polynucleotides
each mononucleotide contains a phosphate group, ribose sugar & nitrogenous base

96
Q

what is the function of messenger RNA?

A

mRNA provides the template for protein synthesis during translation
it exits the nucleus via nuclear pores to ribosomes

97
Q

what is the function of transfer RNA?

A

tRNA brings amino acids & reads the genetic code during translation

98
Q

what is the function of ribosomal RNA?

A

rRNA is found in ribosomes & synthesised in nucleolus
structural & catalytic role during translation

99
Q

describe the process of the formation of polynucleotides

A

polymer of mononucleotides
DNA & RNA form polynucleotides
mononucleotides join by condensation (w the removal of H2O) b/w the phosphate group of one nucleotide & the sugar of another
this forms covalent phosphodiester bonds (phosphate group + 2 ester bonds)
chain of sugars & phosphates = sugar-phosphate backbone, which protects the bases inside the double helix
when polynucleotide is formed, the 5’ phosphate (5th C atom) of the incoming mononucleotide joins to the 3’ hydroxyl group at the end of the chain
2 antiparallel polynucleotide strands twist in opposite directions to form the DNA double-helix
this allows complementary base pairing

100
Q

what direction is DNA synthesised in?

A

5’ to 3’ direction because DNA polymerase only works in 5’ to 3’ direction due to specific shape active site

101
Q

describe the process of semi-conservative DNA replication

A
  1. DNA helicase breaks the H-bonds b/w the base pairs on the polynucleotide DNA strands
    this unwinds the helix to form 2 single strands
  2. each original strand acts as a template for the new strand, which determines the order of bases
  3. complementary base pairing means free-floating DNA nucleotides are attracted to their base pair on the template strand - adenine & thymine & cytosine & guanine
  4. nucleotides join together in a condensation reaction by DNA polymerase
    phosphodiester bonds form b/w adjacent nucleotides
  5. H-bonds form b/w bases on the original & new strands
  6. each new DNA molecule contains 1 strand from the original DNA molecule & 1 new strand
102
Q

what is the evidence for semi-conservative replication?

A

meselson-stahl experiment

103
Q

how does the meselson-stahl experiment provide evidence for semi-conservative replication?

A

experiment with e. coli (fast replication, cheap & easy to manage) grown first in heavy nitrogen (15N) then in lighter isotope (14N)
DNA grown in 15N is more dense than DNA grown in 14N & forms a band at a lower level when spun in an ultracentrifuge
when DNA grown in 15N is switched to media containing 14N after 1 round of cell division, the DNA sediments halfway b/w 15N & 14N levels - shows DNA contains one original 15N strand & one new 14N strand (50%/50%)
as the cells divide, an increasing amount of DNA molecules contain 14N only
DNA contains 50% less 15N after each generation

104
Q

what is ATP?

A

adenosine triphosphate
an RNA nucleotide derivative

105
Q

what is the structure of ATP?

A

adenine - a nitrogenous base
ribose - pentose sugar
phosphate - chain of 3 phosphate groups

106
Q

what are the key features of ATP that make it a good energy-storage molecule?

A

cannot leave the cell
good short-term/immediate energy source
soluble

single step hydrolysis which releases immediate energy
releases a small, manageable quantity of energy

107
Q

why is it important to synthesise a large amount of ATP?

A

ATP cannot be stored - it is an immediate energy source
ATP only releases a small quantity of energy at a time

108
Q

describe the hydrolysis of ATP

A

ATP + H2O –> ADP + Pi (+ energy)
Pi = inorganic phosphate
catalysed by ATPase

109
Q

describe the synthesis of ATP

A

ADP + Pi (+ energy) –> ATP + H2O
catalysed by ATPsynthase
water removed = condensation reaction

110
Q

in what 3 ways does synthesis of ATP happen?

A
  1. oxidative phosphorylation - in plant & animal cells during aerobic respiration in mitochondria
  2. photophosphorylation - in photosynthesis, plants use light energy to synthesise ATP
  3. substrate-level phosphorylation - in plant & animal cells when phosphate groups are transferred from donor molecules to ADP
111
Q

ATP is being continually hydrolysed & resynthesised

A
112
Q

what are the uses of ATP?

A
  1. metabolic processes - ATP is required to make macromolecules
  2. movement - ATP is used for muscle contraction (sliding filament model)
  3. active transport - Na+/K+ ion pump - ATP is needed to change the shape of carrier protein for AT
  4. secretion - ATP is needed to form lysosomes & other vesicles for exocytosis
  5. activation of molecules - transfer of phosphate to activate other molecules by making them more reactive e.g. add P to glucose @ the start of glycolysis
113
Q

why can nucleotides only be added in a 5’ to 3’ direction?

A

DNA polymerase
has a specific shape active site
only complementary with the 5’ end
which is different in shape to the 3’ end

A-Level Biology (5 decks)

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