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OCR Biology A Level Module 2 Foundations in Biology > 2.1.2 Biological Molecules > Flashcards

2.1.2 Biological Molecules Flashcards

1
Q

why is the R group important?

A
  • diff in each amino acid (vary by size, charge and polarity) = varying amino acid chains/sequences = varying protein structures due to varying interactions and bonding which causes it to fold differently.
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2
Q

Why is PO43- important?

A

Inc rigidity of bones, teeth, cartiliage and is component of exoskeleton of crustaceans.
Component of phospholipids, nucleic acids and ATP
Regulation of blood pH
Root growth in plants

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3
Q

Why is OH- important?

A

Regulation of blood pH

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4
Q

Why is NO3- important?

A

Component of amino acids, hormones vitamins and chlorophyll, as well as nucleic acids
Component of nitrogen cycle

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5
Q

Why is NH4+ important?

A

Component of amino acids,hormones, vitamins and chlorophyll and nucleic acids
Regulation of pH
Component of nitrogen cycle

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6
Q

Why is Na+ important?

A

Regulation of osmotic pressure, water levels in body fluid + pH
Affects absorption of carbs in intestine and water in kidneys
Contributes to nervous transmission and muscle contraction
Constituent of vacuole in plants

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7
Q

Why is K+ important?

A

Control of water levels in body fluid + regulates pH
important form of active transport
Synthesis of glycogen and protein
Generates healthy leaves + flowers
Contributes to nervous transmission and muscle contraction
Constituent of vacuole in plants

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8
Q

Why is HCO3- important?

A

Regulation of blood pH
Involved in carbon dioxide transport into and out of blood

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9
Q

Why is H+ important?

A

Photosynthesis and respiration
Oxygen and carbon dioxide transport in blood
Regulation of blood pH

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10
Q

Why is Cl- important?

A

Helps in production of urine in kidney
Transport of carbon dioxide into and out of blood
Regulates affinity of haemoglobin to oxygen
Regulation of blood pH
Used to produce HCl in stomach

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11
Q

Why is Ca2+ important?

A

Increases rigidity of bones, teeth, cartiliage and is a component of exoskeleton in crustaceans.
Clotting blood
Muscle contraction and regulates transmission of nervous impulses
Activator of enzymes such as lipase
Regulates permeability of plasma membranes + imp. for plant cell wall development.

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12
Q

Why does water have a high specific heat capacity? How is this useful?

A

Held together tighly by H bonds - requires a high amount of heat energy to increase the kinetic energy of water ans change the temp.

Living things need a stable temperature for enzyme controlled reactions to happen correctly

the temperature of organisms changes very slowly; less energy needed on temperature control

Aquatic organisms need a thermally stable environment in which to live.

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13
Q

Why does water have a high latent heat of vaporisation and why is it important?

A
  • Molecules held together by H bonds = relatively large amount of heat energy needed for water molecules to spread apart and become a gas.
  • Water can act as an effective coolant (e.g. mammals cooled when sweat evaporates) since it a lot of energy is needed and taken up by the process.
  • Plants are cooled when water evaporates from stomata
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14
Q

Where else is cholesterol/ similar to cholesterol found? And what else does it contribute to?

A

Plants have a derivative in their membranes
Steroid hormones (tesosterone, oestrogen and vitamin C) are made of it and so can pass through the membrane - these are also abundant in plants and on ingestion can be converted into animal hormones.

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15
Q

When dissolved in water, what happens to the amino and carboxyl group?

A

they can IONISE:
-COOH -> COO- + H+ (reversible)
-NH2 + H+ -> -NH3+ (reversible)

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16
Q

What monosaccharides make sucrose? What type of glycosidic bond is it?

A

a-glucose and fructose
1-2

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17
Q

What makes water a liquid? Why is this important?

A

As molecules move they continuously make + break hydrogen bonds - make it more difficult for them to escape to become a gas since more energy is required.
Provides habitat for living things in rivers, lakes and seas.
Major component of tissues
Provide a reaction medium for chemical reactions
Provide an effective transport medium e.g. in blood

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18
Q

What is the structure of phospholipids?

A
  • Glycerol + 2 fatty acids and a phosphate group
  • Condensation reaction
    -In water, the phosphate group has a negative charge making it POLAR/ HYDROPHILIC
  • Fatty acid tails = NON POLAR/ HYDROPHOBIC
  • So phospholipids are amphipathic
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19
Q

Whats the difference between an a-glucose and a b-glucose?

A
  • a-glucose: Hydroxyl is BELOW plane of the ring
  • b-glucose: Hydroxyl is ABOVE plane of the ring
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20
Q

What is the structure and properties of starch?

A

STARCH = large molecule, so is insoluble. –> doesn’t affect the water potential of the cell. Amylose slightly more soluble

amylose:
1. chain of a-glucose formed by 1-4 glycosidic bonds -> easy to break bonds to release glucose
2. coiled into a spiral with H bonds WITHIN molecules to hold it in place + granular -> compact - takes up less space
3. unbranched - no need for as rapid release of monomers in plants

amylopectin:
1. chain of a-glucose formed by 1-4 glycosidic bonds -> easy to break bonds to release glucose
2. coiled into a spiral+ granular -> compact, takes up less space
3. branched due to 1-6 glycosidic bonds, but not as much as glycogen

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21
Q

What is the structure and properties of glycogen?

A
  1. Chain of glucose molecules by 1-4 glycosidic bonds -> easy to break bonds to release glucose
  2. Highly branched due to 1-6 glycosidic -> allows more rapid release of monomers in animals (can be hydrolysed quicker) which is needed due to higher metabolic rate, since there are more ends for glucose to be released.
  3. Large molecule + Insoluble -> doesn’t affect the water potential of the cell
  4. coiled -> compact, high energy content for mass
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22
Q

What is the structure and function of pepsin?

A

Enzyme that digests protein in stomach
1 Polypeptide chain folded into symmetrical tertiary structure.
Very few basic R groups, but many acidic R groups, so stable in acidic environments since it can’t accept many H+ ions
Held together by H bonds and 2 disulfide bridges
no cross links

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23
Q

What is the structure and function of insulin?

A

2 polypeptide chains: A-chain starts with a-helix, and B chain ends with B-pleat. Joined by disulfide links to form overall quaternary structure.
hydrophilic R groups on outside = soluble
made in pancreas, binds to glycoprotein receptors on the outside of muscle and fat cells and liver cells to increase their uptake of glucose

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24
Q

What is the structure and function of haemoglobin?

A

Quaternary stucture made of 4 polypeptides that are a-helices: 2 a-globin chains and 2 b-globin chains (4 subunits of 2 different types)
Shape held by hydrogen, ionic and disulfide bonding, giving the molecule a very specific shape, however it can change shape.
Wide range of amino acids
Hydrophilic groups on outside
4 haem groups (prosthetic groups), containing an iron ion
= CONJUGATED PROTEIN
function is to carry oxygen from lungs to tissues -> an oxygen molecule binds to the iron in lungs, and is released when it reaches the tissues.

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25
Q

What is the general formula for carbohydrates? (With some exceptions)

A
  • Cx(H2O)y​
  • For every carbon there are 2 hydrogen and 1 oxygen GENERALLY
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26
Q

What is the function and structure of cellulose?

A

Function: makes cell walls in plants. support tissues and the whole plant. It prevents bursting when cells are turgid.

Made of b-glucose monomers in chains - every other monomer is rotated by 180 degrees.
H bonding BETWEEN ROTATED GLUCOSE MOLECULES gives the structure strength and stops it spiralling.
H bonding BETWEEN ADJACENT CHAINS/ FIBRILS gives the whole structure additional strength

Chains -> microfibrils -> macrofibrils -> embedded in pectins to form walls
The macrofibrils run in all directions, criss-crossing

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27
Q

What are the properties of cellulose?

A

Tough, strong, insoluble and fibrous, and inert

high tensile strength, fully permeable

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28
Q

What is the function of starch?

A
  • Energy storage in PLANTS
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29
Q

What is the function of keratin? What are its properties?

A

cysteine = lots of disulfide bridges between chains, + H bonding = very strong.
Nails, hair, hoofs, claws, scales, fur etc. Provides mechanical protection, an impermeable barrier to infection, and waterproof so prevents entry of water borne pollutants.

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30
Q

What is the function of glycogen?

A

Energy storage in ANIMALS

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31
Q

What is the function of collagen? What are its properties?

A

artery walls: prevents bursting when withstanding high pressure from blood
tendons: connect muslces to bones
bones, cartilage, and connective tissue
high tensile strength/strong
insoluble
flexible

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32
Q

What is the function and properties of elastin?

A

Strong and extensible
Found in body wherever parts need to stretch or adapt their shape
Skin: can stretch around our bones and muscles
Lungs: allows them to inflate and deflate
Bladder: expands to hold urine
Helps blood vessels to stretch and recoil, helping to maintain the pressure wave of blood

33
Q

What is strange about the density of water? Why is this important?

A

Water becomes more dense as it gets colder ( as you would expect) but only till about 4 degrees celsius. Below this, the hydrogen bonds hold water molecules in a fixed, open lattice structure which is less dense than liquid water.
Aquatic organisms have a stable environment in which to live through the winter since ponds + other bodies of water are insulated against extreme cold since ice is an insulator and floats = habitat.
Provides habitat for animals such as polar bears

34
Q

What is cohesion and surface tension? Why is it important?

A

Water molecules at surface of water are all hydrogen bonded to the molecules next to and beneath them (more attracted than to air molecules above)
This means surface of water contracts (water molecules pulled inwards) and there’s a layer of tension = surface tension (ability to resist force applied)
Hydrogen bonds also makes water cohesive
insects like pond-skaters can walk on it
columns of water can be pulled up the xylem tissue together from the roots.
+ ADHESION

35
Q

What is cholesterol? What is its function?

A
  • Sterol
  • Consists of 4 carbon based rings/ isoprene units
  • Small and hydrophobic - contains a hydrophillic OH group but most of the molecule is hydrophobic
  • Binds/ sits in the middle of the hydrophobic tail part of bilayer and regulates fluidity of the membrane. Increases packing of membrane by binding and therefore reduces fluidity.
  • ( or it can do the opposite, but in exam Q it usually says the above)
36
Q

What else is water important for?

A

REACTANT - in reactions such as photosynthesis and in hydrolysis reactions such as digestion of large biological molecules.

37
Q

What does the tertiary structure involve?

A
  • Further folding = precise, overall 3D SHAPE held in place by bonds between amino acids which lie closely to eachother.
  • either supercoiled (fibrous) or spherical (globular)

hydrogen bonding: between amino groups + carboxyl groups of 2 diff amino acids, or between polar areas of R groups. multiple = strength

ionic bonding: between carboxyl and amino groups that are part of R groups, since they ionise into NH3+ and COO- . strongest attraction

disulfide links: between R groups containing sulfur e.g.in cysteine. strong covalent bonds

38
Q

What does the secondary structure involve?

A
  • Initial folding of polypeptide chain
  • alpha helix or others fold into zig-zag structure and into B-pleated sheet.

Some dont adopt a regular structure and some have more than one
Stable structures at optimal temp and pH

39
Q

What does the primary level of protein stucture involve?

A

sequence of amino acids in a polypeptide chain (number + order determines structure + function)
very strong peptide bonds

40
Q

What does a/b-glucose + b galactose make?

A

Lactose

41
Q

What does a-glucose and a-glucose make?

A

Maltose

42
Q

What does 2 b-glucose molecules make?

A

Cellobiose

43
Q

What are unsaturated fatty acids?

A

at least 1 C=C bond = fewer H atoms can be bonded
Gives it a bend - makes them more fluid - lower m.p and often liquid at 20 degrees celsius
Monounsaturated: 1 C=C bond
Polyunsaturated: >1 C=C bond

44
Q

What are triglycerides made of? How are they formed?

A
  • Condensation reaction between -COOH of fatty acid and -OH of glycerol, where an ester bond is formed.3 x H2O is released
  • Monoglyceride = 1 fatty acid, triglyceride = 3 fatty acids.
45
Q

What are the properties of monosaccharides?

A
  • Sugars which taste sweet
  • Soluble in water but insoluble in non polar solvents
  • White, crystalline solids
    -Readily absorbed = good respiratory substrates
46
Q

What are the main properties of globular proteins?

A

Spherical shape
Hydrophilic R groups on outside
Soluble
Very specific shapes e.g. enzymes and hormones
Metabolically active

47
Q

What are the main properties of fibrous proteins?

A

Regular, repetitive sequences of amino acids
Long, thin
Insoluble
Tend to have structural functions as they can form fibres
Metabolically inactive
Strong

48
Q

What are the functions of triglycerides? (5)

A

Energy source: molecule can be hydrolysed , fatty acids can enter Krebbs cycle. long carbon chains can be broken down in respiration to release energy and generate ATP -acc produces more water than respiration of a sugar.

Energy store: insoluble so don’t affect water potential of the cell. Higher proportion of H atoms and C-H bonds than carbs, so they store more energy in less space.

Insulation: e.g. electrical insulation of neurones. Animals have fat as a heat insulator.

Buoyancy : fat is less dense than water so used by aquatic mammals to help keep them afloat

Protection: humans have fat around delicate organs. There’s also some fat around bacterial cell walls.

49
Q

What are the 2 types of computer modelling?

A
  • Can be used to predict protein shapes

Ab initio protein modelling: model built based on CHEMICAL + ELECTRICAL properties of atoms in each amino acid in the sequence
Comparative protein modelling: protein threading: scans amino acid sequence against database of solved structures and produces a set of possible models.

50
Q

What are some properties of lipids?

A
  • Insoluble in water (non-polar) but soluble in alcohol and acetone.
  • Not polymers since there aren’t repeating units, but are macromolecules
51
Q

What are saturated fatty acids? What is a key property? What is their general formula?

A

No C=C bonds in the molecule.
They can pack closely together = stronger intermolecular forces = often solid at 20 degrees celsius.
General formula is CH3(CH2)nCOOH (end + main chain + carboxyl group)
Ratio of H to C = 2:1

52
Q

What are proteins functions?

A

form structural components, important as enzymes, antibodies and hormones, and as protein constituents such as carrier and channel proteins.

53
Q

What are condensation and hydrolysis reactions?

A
  • Monomers JOINED by CONDENSATION -> covalent bond formed and a water molecule is removed. Almost always when 2 -OH groups react.
  • Polymers broken by HYDROLYSIS -> covalent bond broken and a water molecule is added.
54
Q

What are bacterial cell walls and exoskeletons made of?

A

Bacterial cell walls = peptidoglycan : long polysaccharide chains, cross linked by short peptide chains
Exoskeletons = insect ones made from chitin, with cross links between long chains of acetylglucosamine.

55
Q

Name the elements that make up carbohydrates, lipids, proteins and nucleic acids

A

carbohydrates and lipids: C, H, O
- and P is in phospholipids
proteins: C, H, N, O, S
nucleic acids: C, H, O, N, P

56
Q

Is sucrose reducing or non reducing?

A

Non reducing

All others we need to know are reducing

57
Q

How do you test for starch?

A

Add iodine solution (in potassium iodide) to sample
If starch present, yellow-brown -> blue-black colour change occurs.
When starch dissolved in potassium iodide, the iodine forms I3- ion which goes into middle of amylose helix

58
Q

How many are proteinogenic?

A

20

59
Q

How do you test for reducing sugars in a food sample qualitatively?

A

heat sample with benedicts solution (alkaline copper (II) sulfate)
if reducing sugar is present, colour changes from blue to green to yellow to orange-red
benedicts solution contains Cu2+ ions which are reduced to Cu+ ions, forming an orange-red copper(I) oxide precipitate.

also possible to use reagent test strips. You dip into test solution and compare colour with calibration card

60
Q

How do you test for non reducing sugars?

A

Check for reducing sugars first to make sure there’s none
Take a separate sample and boil it with HCl to hydrolyse the sugar e.g. sucrose into glucose +fructose
Cool solution and add sodium hydrogencarbonate solution to neutralise it.
Test for reducing sugars again - positive result indicates that non-reducing sugar was present.

61
Q

How do you test for lipids?

A

Emulsion test - add ethanol (lipid dissolves to form solution)
Filter and pour solution into water in a clean test tube.
Cloudy white emulsion - made of tiny lipid droplets indicates presence since they’re insoluble in water.

62
Q

How do you do test for proteins in a food sample?

A

Biuret test. If protein is present, colour changes from light blue to lilac.
Made of Biuret A (sodium hydroxide) and Biuret B (copper sulfate)
Colour formed by a complex between nitrogen atom in peptide chain and Cu2+ ions - test detects peptide bonds.

63
Q

How do two or more amino acids join?

A
  • Condensation reaction, water removed.
  • Peptide bond formed
  • 2 amino acids = dipeptide, multiple amino acids = polypeptide
64
Q

How do phospholipids behave in water? What structures do they form? How does this affect a membranes permeability?

A
  • Head faces outwards towards water since it can make H bonds with water
  • Tails face inwards away from water since it cannot make H bonds with water

= BILAYER - free to move in layer but won’t move to any position where the tails are exposed to water = stability
= MICELLE - tiny balls with tails hidden from external environment

  • Partially permeable membranes : only possible for small or non polar molecules to pass through
65
Q

How do hydrophobic and hydrophilic interactions contribute to protein structure?

A

Hydrophobic parts of R groups tend to group together within the interior of the structure to avoid water
Hydrophilic parts face water since they can make H bonds with water
This causes twisting of amino acid chain

66
Q

How do hydrogen bonds occur between water molecules?

A
  • Hydrogen bonds occur between O and H atoms of adjacent molecules since water is polar (has charge separation)
  • Oxygen atom has higher electronegativity due to a greater number of protons, meaning it becomes slightly negative.
  • This leaves the hydrogen atom slightly positive, and so the bond occurs between the slightly positive hydrogen and the slightly negative oxygen of another water molecule.
67
Q

How can water act as a solvent? Why is this important?

A

Polar: slightly positive + slightly negative parts of water molecules are attracted to the positive and negative parts of the solute (ionic compounds usually). They cluster around these and keep them apart

Medium for metabolic reactions in the cytoplasm
Allows ionic compouns to separate
Transport system e.g. blood (oxygen in blood transported)
Organisms can absorb minerals
Able to dilute toxic substances

68
Q

How are disaccharides synthesised and broken down?

A
  • CONDENSATION reaction: forms a glycosidic bond between 2 hydroxyl groups and a water molecule is also released/eliminated.
  • water molecule used in hydrolysis
69
Q

How do you test for reducing sugars quantitatively?

A
  • Centrifuge sample to separate precipitate and any excess solution (supernatant)
  • Pipette supernatant into a cuvette, and place into colorimeter
  • use red light: solution absorbs it, and reflects blue light
  • Device zeroed between each reading by placing a blank sample.
  • Plot a calibration curve using multiple known conc

LOTS of sugars = precipitate increases = amount of copper (II) ions remaining in solution decrease = supernatant less blue = low red light absorption = HIGH transmission.

70
Q

What are biosensors?

A
  • convert a biological/chemical variable to an electrical signal
    can be used to detect contaminants in water, pathogens in food.
71
Q

What is the stationary phase in chromatography?

A
  • chromatography paper or cellulose, OR TLC plate = plastic coated with silica gel.
  • free OH groups pointing outwards, in contact with mobile phase
72
Q

What is the mobile phase in chromatography?

A

solvent, usually water or ethanol

mobile phase flows through and across the stationary phase, carrying the biological molecules with it

73
Q

How do you calculate Rf?

A

distance moved by pigment/ distance moved by solvent front

74
Q

What 3 things can you use in TLC with colourless molecules?

A
  1. UV light - all of plate glows apart from spots
  2. Ninhydrin - binds to amino acids (visible as brown/purple spots)
  3. Iodine - forms a gas which binds to molecules in spots
75
Q

Speed with which molecules move depends on their —- in the solvent and their —–

A highly polar solute will tend to travel how quick? And for non polar?

A

solubility
polarity

WIll tend to adsorb to surface = move slowly
Non polar solute will tend to travel quickly up the plate

76
Q

A student wanted to study the effect of the different sugars on the rate of growth of a yeast
population. They used a colorimeter to measure the absorbance of a culture of yeast cells, which is proportional to the concentration of yeast cells.
As the yeast multiplied, it was necessary to dilute the sample to obtain a reading on the
colorimeter.
(i) Describe how the student could use 1cm3 pipettes and 10cm3 measuring cylinders to
dilute the sample so that it was 10000 times less concentrated.

A

1 correct description of 1:10 dilution
2 need to make , a total of four 1:10 dilutions / three further 1:10 dilutions 
3 correct values of dilutions given between stages e.g.1:10 to 1:100 
4 (ensure) mixing of yeast (suspension) at each stage

77
Q

State a method other than colorimetry for determining the concentration of protein in a solution

A

Biosensor

78
Q

Glycogen is a large polysaccharide. Which option describes the structure and function? A) 1-6 glycosidic bonds are more accessible to enzymes than 1-4 glycosidic bonds so energy can be released more quickly
B) Bonds between B-glucose residues are easily broken by enzymes
C) Exposed OH groups mean it’s soluble
D) Short branches allow more energy storage in small space

A

D

OCR Biology A Level Module 2 Foundations in Biology (6 decks)

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