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A-Level Biology (AQA) > Biological Molecules > Flashcards

Biological Molecules Flashcards

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1
Q

Define ‘monomer’

A

Monomers are the smaller units from which larger molecules are made.

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2
Q

Define ‘polymer’

A

Polymers are molecules made from a large number of monomers joined together.

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3
Q

What is a condensation reaction?

A

A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water.

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4
Q

What is a hydrolysis reaction?

A

A hydrolysis reaction breaks a chemical bond between two molecules and involves the use of a water molecule.

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5
Q

What are the 3 monosaccharides?

A

Glucose
Galactose
Fructose

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6
Q

What are the 2 types of glucose? These are ____ of each other.

A

Two sub-types: alpha-glucose and beta-glucose. Isomers of each other.

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7
Q

Alpha-glucose + alpha-glucose ->

A

-> maltose + water

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8
Q

Alpha-glucose + galactose ->

A

-> lactose + water

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9
Q

Alpha-glucose + fructose ->

A

-> sucrose + water

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10
Q

A _____ bond forms between two monosaccharides

A

glycosidic bond

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11
Q

What is the primary function of starch?

A

Energy source

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12
Q

Starch is found in plants or animals?

A

Plants

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13
Q

Starch: long/short chains of alpha-glucose monomers, linked via ______ bonds
from a _______ reaction

A

Starch: long chains of alpha-glucose monomers, linked via glycosidic bonds
from a condensation reaction

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14
Q

Two types of starch and the key difference between them?

A

— Amylose - unbranched straight chains

— Amylopectin - branched chains

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15
Q

Benefit of amylose’s structure for its function?

A

Unbranched chain is wound into a very tight coil so is compact, storing much energy in a small space

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16
Q

Benefit of amylopectin’s structure for its function?

A

The branching means that multiple enzymes can work on each side chain simultaneously. This ensures quick release of the alpha-glucose monomers that are used in respiration.

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17
Q

Benefit of starch’s general structure for its functions? (x4)

A
  • Insoluble - doesn’t affect water potential, so water is not drawn into cells via osmosis, which would cause them to be turgid
  • Large (and insoluble) - doesn’t diffuse out of cells
  • Compact (amylose) - good for storage (lots of energy, small space)
  • Branching (amylopectin) means it is easily hydrolysed to alpha-glucose - used in respiration
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18
Q

Main function of glycogen? Plants or animals?

A

Energy source in animals/bacteria cells

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19
Q

Structure of glycogen?

A

Short, very highly branched chains of alpha-glucose monomers

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20
Q

Glycogen is stored where and as what?

A

Stored as small granules in muscles and the liver

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21
Q

Adaptations of the structure of glycogen for its functions? X3

A
  • Insoluble - doesn’t affect water potential, so water is not drawn into cells via osmosis. Also does not diffuse out of cells.
  • Compact - good for storage (lots of energy, small space)
  • Highly branched - means it is easily hydrolysed to alpha-glucose - used in respiration
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22
Q

Structure of cellulose? (3 levels)

A

Straight, unbranched chains of beta-glucose

Chains run parallel to each other, with cross-linkages between them. This forms microfibrils, which have a great collective strength

Parallel microfibrils then form fibres

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23
Q

What forms between chains of cellulose monomers? How?

A

Hydrogen bonds form cross bridges, via -OH groups on either side of the monomers

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24
Q

Function of cellulose? How and why is this important?

A

Structural support of the cell wall: the cell wall exerts an inward pressure into the cell that stops any influx of water, ensuring the cell does not burst due to osmotic changes

This semi-rigid state is essential to maintaining turgor of stems and leaf cells (maximum surface area for photosynthesis)

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25
Q

Lipids contain what elements?

A

Carbon, hydrogen, oxygen

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26
Q

In lipids, the proportion of oxygen to hydrogen and carbon is _____ than in carbohydrates. Consequence?

A

Proportion of oxygen to hydrogen and carbon is smaller than in carbohydrates. This means that more energy is released per mass when lipids are hydrolysed, than with carbohydrates.

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27
Q

Are lipids soluble?

A

Insoluble in water

Soluble in organic solvents such as ethanol

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28
Q

Roles of lipids? X4

A
  • Energy source
  • Waterproofing (insoluble in water; act as waxy cuticle in plants to conserve water)
  • Insulation
  • Protection (fat around delicate organs)
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29
Q

Structure of glycogen?

A

CH2OHCHOHCH2OH

30
Q

How do you form a triglyceride?

A

Glycerol + 3xfatty acids -> triglyceride + 3H2O

31
Q

What is the bond between the glycerol and fatty acid chain in a triglyceride?

A

The bond between the glycerol and fatty acid chain is an ‘ester bond’ - C-O-C

32
Q

Why do differences between triglycerides arise?

A

Differences between triglycerides arise from variation in the R-group: the fatty acid chain

33
Q

Structure and functional adaptations of triglycerides?

A
  • Insoluble (does not affect water potential/water in/out by osmosis)
  • Low mass to energy ratio: low mass but lots of energy stored
  • High ratio of C-H bonds to C atoms (which store energy)
  • High ratio H:O atoms - release water
34
Q

Structure of phospholipids?

A

Two fatty acids, glycerol and phosphate molecule

Hydrophilic head and hydrophobic tail

35
Q

Phospholipids are non-polar molecules. True/false?

A

False = polar molecule

36
Q

Test for lipids?

A
  1. Clean dry grease-free test tube
  2. Take 2cm3 of sample and 5cm3 ethanol
  3. Shake tube throughly (to dissolve sample)
  4. Add 5cm3 water and shake gently

Pos: white-emulsion
Neg: no visible change

37
Q

Why does a white-emulsion form in the test for lipids?

A

Lipid in the sample becomes finely dispersed in the sample to form an emulsion. Light is refracted as it passes through water and oil droplets, appearing cloudy

38
Q

What should you do for a control with the test for lipids?

A

Repeat the procedures using water instead of a sample. It should remain a clear solution, not cloudy

39
Q

General structure of amino acids?

A

Amino group - CHR - carboxyl group

NH2) - CHR - (COOH

40
Q

What forms when two amino acids combine via a condensation reaction?

A

Forms a dipeptide, one molecule of water and a peptide bond

41
Q

What are the four protein structures?

A

Primary - sequence of amino acids
Secondary - alpha-helix or beta pleated sheet
Tertiary - 3D folded structure of protein
Quaternary - multiple polypeptides

42
Q

Bonding in primary protein structure?

A

Peptide bonds

43
Q

Bonding in secondary protein structure?

A

Hydrogen bonding

44
Q

Bonding in tertiary protein structure?

A

Disulphide bridges between thiol groups in cysteine (very strong);

Ionic bonds between any -NH2 and -COOH groups not used in the peptide bonds (weak);

Hydrogen bonds (numerous but weak);

45
Q

Test for proteins?

A

Biuret Test:

  • Add 2 cm3 of the liquid food sample* to a clean, dry test tube
  • Add 2 cm3 of Biuret Reagent.
  • Shake well and allow the mixture to stand for 5 minutes
  • Observe any color change.

Pos: purple solution
Neg: remains blue solution

46
Q

Control for protein test?

A

Repeat steps with de-ionized water to prepare a negative control and with albumin (egg white) to prepare a positive control.

47
Q

What is the Lock and Key Mechanism?

A

‘Enzymes are specific. Only molecules with the correct shape can fit into the enzyme. Just like only one key can open a lock, only one type of enzyme can speed up a specific reaction. This is called the lock and key model.’

48
Q

What is the Induced Fit Mechanism?

A

The shape of Active Sites are not exactly Complementary, but change shape in the presence of a specific substrate to become Complementary.
When a substrate molecule collides with an enzyme, if its composition is specifically correct, the shape of the enzyme’s Active Site will change so that the substrate fits into it and an Enzyme-Substrate Complex can form. The reaction is then catalysed and an Enzyme-Product Complex forms.

49
Q

How does an enzyme catalyse a reaction?

A

As the enzyme shape changes, this places strain on the substrate molecule. This distorts particular bonds in the substrate, thus lowering the activation energy required to break those bonds.

50
Q

Two types of enzyme inhibition?

A

Competitive and non-competitive

51
Q

Describe competitive enzyme inhibition

A

Competitive: the inhibitor is a complementary shape to the active site of the enzyme. It binds to the active site and blocks any substrates, so enzyme-substrate complexes cannot form. Reversible.

52
Q

Describe non-competitive enzyme inhibition

A

Non-competitive: the inhibitor binds to another depression on the enzyme called the allosteric site. This causes a conformational shape change in the active site of the enzyme, so its substrate is no longer complementary in shape and enzyme-substrate complexes cannot form. Irreversible.

53
Q

What are the 3 components of a nucleotide? (DNA/RNA)

A

Phosphate group - (deoxy)ribose sugar - nitrogenous base

54
Q

DNA nitrogenous bases?

A

Adenine = thymine

Guanine - - - Cytosine

55
Q

RNA nitrogenous bases?

A

Uracil = adenine

Guanine - - - Cytosine

56
Q

Describe the structure of DNA x5

A
  • Sugar-phosphate backbone formed via condensation reaction between phosphates and deoxyribose sugar (-> H2O)
  • Hydrogen bonds between complementary bases (adenine and thymine - 2x hydrogen bonds, guanine and cytosine - 3x hydrogen bonds)
  • Double helix
  • Long molecule
  • Coiled around histone proteins (compact)
57
Q

Why is DNA a stable molecule? x2

A
  • Phosphodiester backbone protects more reactive bases

- Hydrogen bonds link complementary bases (G- - -C has 3x H-bonds so more G/C = more stable)

58
Q

DNA Structure and Function adaptations? x4

A
  • H-bonds are weak enough to be overcome and allow DNA replication
  • Very large molecule: contains LOTS of genetic info
  • Base pairing allows transcription to mRNA and protein synthesis (translation)
  • Rarely mutates
59
Q

Describe DNA Replication x5

A

1 - DNA Helicase breaks hydrogen bonds between complementary DNA bases
2 - Free activated nucleotides bind to their complementary bases
3 - DNA polymerase reforms the phosphodiester backbone once the complementary bases have paired up

60
Q

DNA Replication is….?

A

Semi - Conservative

61
Q

ATP stands for?

A

Adenosine Triphosphate

62
Q

Structure of ATP?

A

Adenine - ribose sugar - 3x phosphate groups

63
Q

ATP equation? Enzymes?

A

ATP + H2O ADP + P1

Forward: ATP hydrolase
Backward: ATP synthase

64
Q

5x uses of ATP?

A
  • Activation of molecules (e.g. activation of glucose molecules at start of glycolysis)
  • Active transport (e.g. absorption of AAs across ileum with sodium/potassium ion pump)
  • Muscle contraction (actinomyosin cross-bridges)
  • Metabolic processes
  • Secretion
65
Q

Advantages of ATP for its functions? x3

A
  • Releases energy in small amounts when hydrolysed, which match the needs of cellular reactions
  • Can move around easily in a cell but doesn’t leave the cell
  • Releases energy quickly – one step reaction
66
Q

Is water polar?

A

Water is a polar molecule: oxygen is electronegative; hydrogen is electropositive

67
Q

5x functions of water and advantages?

A
  • Cohesion (xylem tissues)
  • Metabolite (hydrolysis reactions)
  • High-latent heat of vaporisation (sweat cooling mechanism)
  • Ice is dense (insulates water underneath - temperature stability)
  • High specific heat capacity (temperature stability)
68
Q

4x key inorganic ions?

A

Iron ion, Fe^2+
Hydrogen ion, H+
Sodium ion, Na+
Phosphate ion, PO4^3-

69
Q

Importance of Iron ion, Fe^2+?

A

Needed to make haemoglobin – found in red blood cells.

Haemoglobin used to carry oxygen round the body.

70
Q

Importance of Hydrogen ion, H+?

A

Cause solutions to become acidic.
Buffers are used to prevent pH changes.
Enzymes denatured when pH changes.

71
Q

Importance of Sodium ion, Na+?

A

Needed to transport glucose into cells.
Causes high blood pressure – changes water potential of blood.
Use to produce electrical impulses in nerve cells

72
Q

Importance of Phosphate ion, PO4^3-?

A

Needed to make vital biological molecules:
Phospholipids for membranes
DNA/RNA
ATP

A-Level Biology (AQA) (7 decks)

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