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OCR Biology A Level > 2.1.2 Biological Molecules > Flashcards

2.1.2 Biological Molecules Flashcards

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1
Q

Define a carbohydrate

A
  • Contains carbon, hydrogen, and oxygen
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2
Q

Explain how carbohydrates are classified and give examples

A

Sugars
- monosaccharides - glucose, fructose, galactose
- disaccharides - sucrose, maltose, lactose

Polysaccharides
- storage - glycogen, starch
- structural - cellulose

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3
Q

Characteristics of a monosaccharide?

A
  • are soluble in water
  • have a sweet taste
  • form crystals
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4
Q

Explain how the amount of carbons ina sugar correlates to the type of monosaccharide

A
  • if they have 3 carbons they are triose sugars
  • 5 carbons = pentose sugar
  • 6 carbons = hexose sugar
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5
Q

What is the general formula of a monosaccharide?

A

(CHO2O)n, where n is >= to 3

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6
Q

Explain how you distinguish between a-glucose and b-glucose

A
  • In a-glucose the OH group on carbon 1 is below the plane of the ring
  • In b-glucose the OH group on carbon 1 is above the plane of the ring
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7
Q

How does glucose contasing lots of bonds relate to it’s function?

A

It can contain lots of energy

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8
Q

What is a disaccharide?

A

Sugars composde of two monosaccharides bopnded together by a glycosidic bond

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9
Q

What monosaccharides make up:
- maltose
- sucrose
- lactose

A
  • maltose = glucose + glucose
  • sucrose = glucose + fructose
  • lactose = glucose + galactose
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10
Q

How is a a-1,4-glycosidic bond formed?

A
  • between carbon 1 of one glucose molecule and carbon 4 of another glucose molecule
  • two OH groups bond to form a water molecule (H2O)
  • O boned to carbon in one molecule and carbon in another
  • C-O-C link formed
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11
Q

What are the two types of storage polysaccharides and in which species are they found

A
  • starch - plants
  • glycogen - animals
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12
Q

What are the two different polysaccharides that make up starch?

A
  • amylose (coiled)
  • amylopectin (coiled and branched)
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13
Q

What bonds do amylose and amylopectin use?

A
  • amylose = a-1.4-glycosidic bonds
  • amylopectin = a-1,4glycosidic + a-1,6 glycosidic bonds
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14
Q

Give key points about starch

A
  • carbohydrate consiting of two polysacchardies, amylose and amylopectin
  • stored in chloroplast and elsewhere in plants
  • stored in cells as starch grains
  • can be broken down into a-glucose which are respired to produce ATP
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15
Q

Explain the structure of glycogen

A
  • a-1,4glycosidic + a-1,6 glycosidic bonds
  • same overall satrucutre as amylopectin, but signifficantly more branching and 1,4 chains are smaller
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16
Q

Where and how is glucose stored?

A
  • stored as glycogen granules
  • found in large amounts in the liver + skeletal muscles
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17
Q

Give key points about glycogen

A
  • polymer of a-1,4 glycosidic bonds
  • many side chains due to a-1,6 glycosidic bonds
  • insoluble, compact, energy dense
  • does not affect water poetion of cell
  • branches for rapid hydrolysis by enzymes
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18
Q

How do storage polysacchrides’s structures and properties relate to their function?

A

Structure
- both are made by bonding thousands of a-glucose molecules together (condenstation reactions)
- a-glucose stored is used in respiration

Function
- compact - lots of energy stored in small volume (energy dense)
- metagbolically inactive (doesn’t take part in metabolic reactions)
- insoluble in water - do not dissolve in water, so does not affect cell water potential
- chain molecules - glkucose held by chains which can be hydrolysed by enzymes
- branched - branches ahve ends where enzymes can add or remove glucose - can be quickly hydrolysed

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19
Q

Give an example of a structural polysaccharide and it’s properties

A

cellulose - high tensdile strength + insoluble

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20
Q

Explain the structure of the cell wall, and the glucose used

A
  • beta glucose
  • forms cellulose fibres, which form microfibril, which form macrofibril, which form the wall
  • alternate beta glucose molectules roatet 180 degress - forms hydrogen bonds between OH groups
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21
Q

Give examples of lipids

A

triglycerides, phospholipids and steroid alcohols

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22
Q

Explain the key functions of lipids

A

Triglycerides
- enmergy storage and source
- insulation
- protection of organms

Phospholipds
- plasma membrane

Sterols
- make up some hormones

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23
Q

Explain the structure of a triglyceride

A
  • made from 1 glyercol + 3 fatty acids
  • not built from repeating units - not a polymer
  • macromlecule - a large molecule
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24
Q

Why is water a polar molecule?

A
  • more positive protons in its nucleus
  • uneven distribution of electrons
  • oxygen atoms become partially negative
  • hydrogen atoms become partially positive
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25
Q

Give key aspects of hydrogen bonds

A
  • weak electrostatic interaction
  • molecules contain a partially negativley charged atom (N,O,F) bonded to partially positivley charged hydrogen atom
  • weaker than a covalent bond
  • thousands of hydrogen bonds can stabalise structures
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26
Q

Define metabolism

A

All the biochemical reactions happening inside the cells of an organism

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27
Q

What are catabolic and anabolic reactions?

A

Catabolic reactions: Breaking down large molecules (hydrolysis reactions)
Anabolic reactions: Building large molecules (condensation reactions)

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28
Q

What are the functions of carbohydrates?

A
  • energy storage and supply
  • structure (plant cellulose cell wall)
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29
Q

What are the functions of proteins?

A
  • structure (keratin in hair, collagen in skin)
  • transport (channel and carrier)
  • enymes
  • antibodies
  • most hormones
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30
Q

What are the functions of lipids?

A
  • plasma membranes
  • energy storage and supply
  • insulation of animals
  • nerve cell insulation
  • some hormones (steroid hormones)
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31
Q

What are the functions of vitamins and minerals?

A
  • form parts of larger molecules
  • vitamins used as co-enzymes
  • minerals used as inorganic cofactors + prosthetic groups
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32
Q

What are the functions of nucleic acids?

A
  • contain genes that code the amino acid sequence of proteins
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33
Q

What are the functions of water?

A
  • support plants
  • solvent for metabolic reactions
  • transport medium
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34
Q

Give key aspects of carbon

A
  • 4 electrons in its outer shell
  • becomes stable via sharing 4 outer electrons with other atoms (8 electrons in outer shell)
  • forms covalent bonds (single or double)
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35
Q

What is the difference between a monomer and a polymer?

A

Monomer: Single molecule units repeated to make polymers
Polymers: Large molecules made from joining monomers together (Monomers must be of the same type)

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36
Q

Give examples of monomers and polymers of carbohydrates

A

Monomer: Monosaccharide e.g. glucose/fructose/galactose
Polymer: Polysaccharide e.g. starch/cellulose/glycogen

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37
Q

Give examples of monomers and polymers of proteins

A

Monomer: Amino acids e.g. Glycine/Tyrosine
Polymer: Polypeptides + proteins e.g. haemoglobin/enzymes

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38
Q

Give examples of monomers and polymers of nucleic acids

A

Monomer: Nucleotides
Polymer: Polynucleotides e.g. DNA & RNA

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39
Q

Give key aspects of hydrolysis

A
  • water molecule used
  • covalent bond breaks
  • monomer molecules from polymer
  • normally requires an enzyme
  • e.g. digestion
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40
Q

Give key aspects of condensation

A
  • water molecule is released
  • covalent bond forms
  • polymer molecules from monomers
  • normally requires an enzyme
  • e.g. protein synthesis
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41
Q

Give key aspects of water

A
  • polar molecules
  • the oxygen attracts the pair of electrons in the O-H bond more strongly thean the hydrogen atom
  • oxygen atom has delta negatie charge
  • hydrogen atom has delta positive charge
  • hydrogen bonds ^
42
Q

Give important properties of water that play important roles in living organisms

A
  • water is a liquid
  • water is a solvent
  • there are cohesive forces between H20 molecules in water
  • density when water freezes
  • water has thermal stability
  • water is a reactant
43
Q

Explain why water is a liquid at room temperature and the biological importance of it.

A

Why
- hydrogen bonds form between water molecules, forming a network that allows the molecules to move around, continually making + breaking hydrogen bonds

Importance
- used as a transport medium in animal blood
- used as a transport medium in vascular tissues in plants
- used as a habitat by prokaryotic organsisms e.g. Cholera

44
Q

Explain why polar molecules are able to dissolve in water and the biological importance of it

A

Why
- polar ions are soluble in water - water is attracted to the ions/polar molecules, clusters around them and seperates them

Importance
- allows ionic compounds to seperate
- medium for metabolic reactions
- repsiration + photosynthesis relies on reactants dissolved in water to react
- liquid transport medium
- organisms can take in dissolved mineral ions
- dissolves toxic substances

45
Q

Explain why there is cohesion between water molecules biological importance of it.

A

Why
- hydrogen bonds force water molecules to stick to each other

Importance
- water can move up xylem in transpiration stream by forming strong water collumns
- creates surface tension on water surface - habitat for invertebrates

46
Q

Explain why water density decreases under 0 degrees and the biological importance of it.

A

Why
- as water cools its density decreaes - molecules spread out more
- due to more and longer hydrogen bonds forming between H20 molecules, creating an oppen lattice structure
- ice is less dense than water so floats on liquid water

Importance
- forms ice on the surface of the water
- creates a habitat + insulates water below causing aquatic organisms no to freeze

47
Q

Explain why water has a high specific heat capacity and the biological importance of it.

A

Why
- a large amount of energy is needed to raise the temperature of water
- many stable hydrogen bonds between water molecules that need to be broken

Importance
- temperatue of large bodies of water (lakes + oceans) remains stable even when outsaide temperature changes dramatically
- provides thermally stable environment for aquatic + prokaryotic organisms
- temperatues change very slowly so organisms use less energy on temperature control
- prevents internal temperature inside organisms changing quickly so enzymes can function properly

48
Q

Explain why water has a high latent heat of vaporisation and the biological importance of it.

A

Why
- the evaporation of water uses up a large amount of energy
- many stable hydrogen bonds between water molecules that need to be broken

Importance
- water evaporating from the surface ‘removes’ heat, cooling the organism down
- organisms usae water as an efficient cooling mechanism (panting, transporation, sweating)

49
Q

Water has thermal stability - explain the difference between high specific heat capacity and high latent heat of vaporisation

A

High specific heat capacity: A relativley large amount of energy is needed to raise the temperature of the water
High latent heat of vaporisation: The evaporation of water (liquid to gas) uses up a relativley large amount of energy

50
Q

Explain the biological importance of water being a reactant in chemical proccesses inside cells (metabolism)?

A
  • water used in photosynthesis
  • water molecules used in hydrolysis reactations
51
Q

Explain the structure of an amino acid

A
  • amino groups
  • R group
  • carboxyl group
52
Q

Give key aspects of amino acids

A
  • 20 amino acids due to 20 different R-groups
  • you make 12
  • 8 ‘essential’ amino acids needed in your diet
  • some R-groups are polar so are hydrophillic (water loving)
  • some R-groups are non-polar so are hydrophobic (water repelling)
53
Q

What is a dipeptide and polypeptide

A

Dipeptide: Two polypeptides bonded together
Polypeptide: More than two polypeptides bonded together

54
Q

How is a dipeptide formed?

A
  • condensation reaction
  • peptide bond formed
  • OH group of carboxyl group of one amino acids bonds with H atom of amino group of another acid to form H20
  • C + N atoms bond
55
Q

How is dipeptide broken down?

A
  • hydrolysis reaction
  • peptide bond broken
  • amino acids made from the dipeptide
  • water used up
  • C-N bond of peptide bond breaks
  • OH group of water joins to C of peptide bond to reform carboxyl group
  • H atom left over from h20 bonds to the N of the peptide bond to reform the amino group
56
Q

What are the 4 levels of protein structure?

A
  • primary structure
  • secondary structure
  • tertiary structure
  • quaternary structure
57
Q

Define primary structure

A

The specific sequence of amino acids in the protein chain

58
Q

How is an alpha helix formed

A
  • when polypeptide chains coil to for ma helix
  • shape is held together via hydrogen bonds
58
Q

Define secondary structure and the twp types

A

The coiling and pleating of parts of the polypeptide chain
- alpha helix - the most common secondary structure
- beta pleated sheets
- both are held together via hydrogen bonds

59
Q

How is tertiary structure held in place?

A
  • hydrogen bonds between polar groups
  • disulphide bonds (covalent) form between sulphurs in R groups of the amino acids cysteine
  • ionic bonds between positively + negatively charged R groups of amino acids
  • hydrophobic interactions between non-polar R groups which cluster together towards the centre of the molecule]0 hydrophilic interactions outside of molecule with contact with water
59
Q

Define tertiary structure

A

When secondary A helix + B pleated sheets gold further to give a complex and specific 3-D shape

59
Q

How are Beta pleated sheets formed

A
  • polypeptide chain folds so sections of the chain are parallel
  • held together via hydrogen bonds
  • pattern formed by the individual amino acids causing the structure to look pleated
60
Q

Give examples of proteins with tertiary structure

A
  • antibodies
  • antigens
  • enzymes
  • their tertiary structures are specific shape to only one substance
61
Q

How are tertiary structures denatured?

A

Heat gives kinetic energy (vibrations) which cause hydrogen bonds to break first, and then ionic bonds
- disulphide bonds will eventually break due to heat but only at 1000s degrees

62
Q

Define Quaternary structure

A

Proteins with more than one polypeptide chain

63
Q

Give an example of a Quaternary structure

A

Haemoglobin
- 4 polypeptide chains
- 2 a chains + 2 b chains
- each chain has a haem prosthetic group which contains a Fe2+ ion (conjugated)
- carries oxygen from lungs to respiring tissue for aerobic respiration

64
Q

Give other examples of proteins with quaternary structure

A

Catalase + Collagen

65
Q

What are the two types of 3-D shape molecules can be?

A

Globular or Fibrous

66
Q

Give key details about globular proteins

A
  • folds into a compact ball-shaped spherical structure
  • hydrophobic R-groups turn inwards to centre of protein
  • hydrophilic R-groups on the outside means they’re more water soluble as water molecules can cluster around the protein
  • have metabolic roles e.g. enzymes, plasma proteins, antibodies
  • water soluble
67
Q

Give key aspects of Catalase

A
  • globular protein
  • enzyme (speeds up metabolic reactions)
  • specific shaped active site for a specific substrate molecule
  • quaternary structure with 4 haem prosthetic groups
  • presence of Fe2+ ions allows increased sped breaking down hydrogen peroxide
  • hydrogen peroxide made in metabolic reactions and can damage cells if allowed to accumulate
68
Q

Give key aspects of Insulin

A
  • globular protein
  • transported in blood
  • hormone regulating blood glucose concentration
  • fits into binding sites in specific receptors on cell surface membrane of muscle/liver cells
  • needs precise + specific 3D shape
  • secreted as pro-insulin
69
Q

Give key aspects of fibrous proteins

A
  • formed from long chains of amino acids + are insoluble molecules
  • high proportion of amino acids with hydrophobic R-groups in primary structure
  • limited range of amino acids - usually have small R-groups
  • regular, repetitive sequences of amino acids
  • little tertiary structure
  • very organised structure
  • structural roles e.g. myosin in muscles, keratin in hair, collagen in skin
70
Q

Give key aspects of keratin

A
  • group of fibrous proteins present in hair, skin + nails
  • a helixes held together by many cysteine amino acids forming many disulphide bonds
  • forms strong, inflexible, insoluble molecules
  • more cysteine amino acids = more disulphide bonds = stronger the structure
  • nails have more disulphide bonds than hair so less flexible
71
Q

Where is collagen found?

A
  • walls of arteries
  • tendons
  • bones
  • cartilage
  • cosmetic treatments
72
Q

Give key aspects of collagen

A
  • made up of three polypeptide chains wound around each other to form a triple helix
  • forms a long, rope like structure
  • some flexibility
  • each polypeptide chain itself is a helix
73
Q

Give key aspects of elastin

A
  • fibrous protein found in elastic fibres
  • found in blood vessels + alveoli
  • give structure flexibility to expand when needed, nut return to normal size afterwards
  • allows for stretch + recoil
  • quaternary protein made of many stretchy molecules called tropoelastin
74
Q

What is qualitative test?

A

Tests for the presence or absence of a particular biological molecules
- does not tell you the concentration of a particular biological molecule in the solution

75
Q

What can you qualitative test for?

A
  • starch - iodine solution
  • reducing sugar (e.g. glucose) - Benedicts solution + heat
  • protein - Biuret solution
  • lipid - alcohol emulsion test
76
Q

Explain the test for starch and the positive + negative results

A
  • add one drop of iodine solution
    Positive result: Blue/black
    Negative result: Yellow colour
77
Q

Explain the test for reducing sugar and the positive + negative results

A
  • Uses Benedict’s solution
    1. Add Benedict’s solution to sample in test tube
    2. Shake mixture + heat - don’t boil (80 degrees)
    Positive result: Red precipitate
    Negative result: Blue precipitate
  • can be a range of colours - semi-quantitative
78
Q

How do you edit the test for reducing sugar for non-reducing sugars and the positive + negative results

A
  • non-reducing sugars do not give a positive with Benedict’s reagent
    1. Boil with dilute hydrochloric acid
    2. Neutralise with sodium carbonate
    3. Repeat Benedict’s test
79
Q

What can be used to test for reducing sugars?

A

Diastix + Clinistix

80
Q

What are the advantages + disadvantages of Diastix & Clinstix

A

Advantages
- quick
- just need urine sample
- may tests can be done at once
- no labs required

Disadvantages
- subjective in terms of colour
- colour blindness
- not many intermediate values

81
Q

Explain the test for protein and the positive + negative results

A
  • uses Biruet solution
    1. Add Biuret solution
    2. Shake thoroughly
    Positive result: Lilac colour
    Negative result: Blue colour
82
Q

Explain the test for lipids and the positive + negative results

A
  • uses Ethanol & water
    1. Crush sample (if needed)
    2. Add ethanol to sample
    3. Shake
    4. Pour into water

Positive result: White emulsion obtained
Negative result: No cloudy white emulsion

83
Q

Give key aspects of a colorimeter

A
  • device that shines a beam of light through a sample
  • a photoelectric cell picks up the light that has passed through
  • sample of the solution placed between the light and photoelectric cell in a cuvette
  • advantage of using a colorimeter is that is is not subjective + less affected by human error
84
Q

What is a colorimeter absorbance & transmission?

A
  • colorimeters can be set to absorbance or transmission
  • before they are used they are set to 0% absorbance/transmission
  • 0% absorbance to record absorbance
  • 0% transmission to record transmission
85
Q

What is a blank?

A

A blank is used to calibrate a colorimeter
- distilled water for absorbance
- unreacted benedicts for transmission

86
Q

Why is a red filter used in the colorimeter

A
  • the filter absorbs all parts of the visible spectrum apart from red (including blue)
  • this will only transmit red light to the blue solution in the cuvette, no blue light will be transmitted
87
Q

How is a calibration curve constructed?

A
  • known concentrations of glucose are used and a Benedict’s test is carried out on each known concentration of glucose
  • the precipitate is filtered out of the solution + a red filter is used
  • a colorimeter is used to give readintgs of light passing through light/absorbed
  • the readings are plotted on a graph to show transmission or absorbance on y-axis against sugar concentration on x-axis
88
Q

What variables need to be controlled when measurring the concentration of a reducing sugar

A
  • same volume of glucose solution
  • same volume of Benedcit’s solution
  • same concentration of Benedict’s solution
  • Heat to 80 degrees for same length of time
  • calibrate colorimeter
  • same red filter/colorimeter
89
Q

What other quantitative methods can be used to determine glucose concentration

A
  • use biosensor
  • use clinistix/diastix
90
Q

What is TLC?

A

Thin layer chromatography - used to seperate vitamins, amino acids, carbohydrates, proteins, amino acids and pigments

91
Q

What is the stationary phase?

A

The chromatography strip

92
Q

What is the mobile phase?

A

The liquid solvent

93
Q

How is TLC carried out?

A

The mobile phase flows through the stationary phase and carries the components of the mixture with it

94
Q

What are the stationary phase made of?

A

A thin, uniform layer of silica gel or alumina coated on to a piece of glass, metal or rigid plasticW

95
Q

In TLC, waht is the distance travelled determined by?

A
  • solubility of the compound moving in the solvent
  • the interaction between the compound moving and the silica gel
96
Q

How is the Rf value for a compound worked out?

A

R1 = distance travelled by component/distance travelled by solvent

97
Q

Where should TLC be measured from?

A

The baseline, not the endo f the chromatogram

98
Q
A
99
Q

What rule should Rf values be?

A

Should always be less than 1
(Jf greater than 1, probably completed the divison wrong way round)

OCR Biology A Level (21 decks)

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