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a-level biology > Biological Molecules- Substances ( Year 12 content ) > Flashcards

Biological Molecules- Substances ( Year 12 content ) Flashcards

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AP® Biology flashcards
1
Q

Define monomer. Give some examples

A

A smaller unit that joins together to form a larger molecule
●monosaccharides(glucose,fructose and galactose)
●amino acids
●nucleotides

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2
Q

Define polymer. Give some examples

A

Molecules formed when many monomers join together
●polysaccharides
●proteins
●DNA/RNA

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3
Q

What happens in a condensation reaction?

A

A chemical bond forms between 2 molecules and a molecule of water is produced

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4
Q

What happens in a hydrolysis reaction?

A

A water molecule is used to break a chemical bond between 2 molecules

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5
Q

Name the 3 hexose monosaccharides

A

●glucose
●fructose
●galactose
All have the molecular formula C6H12O6

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6
Q

Name the type of bond formed when monosaccharides react

A

(1,4 or 1,6) glycosidic bond
2 monomers= 1 chemical bond= disaccharides
Multiple monomers= many chemical bonds= polysaccharides

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7
Q

Name 3 disaccharides. Describe how they form

A

Condensation reaction forms glycosidic bond between 2 monosaccharides
●maltose: glucose+glucose
●sucrose: glucose+fructose
●lactose: glucose+ galactose

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8
Q

Draw the structure of alpha glucose

A

The hydroxile group(-OH) bonded to carbon 1 is below

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9
Q

Draw the structure of beta glucose

A

The hydroxile group(-OH) bonded to carbon 1 is above

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10
Q

Describe the structure and function of starch

A

Storage polymer of alpha glucose in plant cells
●insoluble=no osmotic effect on cells
●large= doesn’t diffuse out of cells
Made from amylose:
●1,4 glycosidic bonds
● helix with intermolecular hydrogen bonds=compact
And amylopectin:
●1,4 and 1,6 glycosidic bonds
● branched= many terminal ends for hydrolysis into glucose

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11
Q

Describe the structure and functions of glycogen

A

Main storage polymer of alpha glucose in animals cells
●1,4 and 1,6 glycosidic bonds
●branched= many terminal ends for hydrolysis
●Insoluble=no osmotic effect
●compact

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12
Q

Describe the structure and functions of cellulose

A

Polymer of beta glucose gives rigidity to plant cells walls
●1,4 glycosidic bonds
●straight chain, unbranded molecule
● alternate glucose molecules are rotated 180°
● hydrogen crosswinds between parallel strands form microfibrils=high tensile strength

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13
Q

Describe the benedicts test for reducing sugars

A

1) add equal volume of benedicts reagent to a sample
2)heat the mixture in an electric water bath at 100°C for 5 mins
3) Positive result: colour change from blue to orange and brick-red precipitate forms

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14
Q

Describe the benedicts test for non-reducing sugars

A

1) negative result: benedicts reagent remains blue
2) heat the sample in hydrochloric acid
3) neutralise the mixture using sodium carbonate solution
4) proceed with the benedicts test as usual.

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15
Q

Describe the test for starch

A

1) add iodine solution
2) positive result: colour change from orange to blue-black

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16
Q

Describe how to test for lipids in a sample

A

1) dissolve sample in ethanol
2) add a equal volume of water and shake
3) positive result: milky white emulsion forms

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17
Q

How do triglycerides form?

A

condensation reaction between 1 molecule of glycerol and 3 fatty acids forms ester bonds

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18
Q

contrast saturated and unsaturated fatty acids

A

Saturated
-contains only single bonds
-straight chain molecules
-Higher melting point=solid at room temperature
-found in animal fats
Unsaturated
-contains double C=C bonds
-‘kinked’ molecules
-lower melting points=liquid at room temperature
-found in plant oil

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19
Q
A
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20
Q

Relate the structure of triglycerides to their functions.

A

●High energy:mass ratio=high calorific value from oxidation
●Insoluble hydrocarbon chain=no effect on water potential
●less dense than water=buoyancy of aquatic animals

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21
Q

Describe the structure and function of phospholipids.

A

A glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head.
●Forms phospholipid bilayer in water
●Tails can splay outwards=waterproofing

22
Q

Compare phospholipids and triglycerides.

A

●Both have a glycerol backbone
●Both contain the elements C,H,O
●Both formed by condensation reaction

23
Q

Why is water a polar molecule?

A

O is more electronegative than H, so it attracts the shared pair of electrons in the covalent bond more strongly.
O is delta negative
H is delta positive

24
Q

State 5 important properties of water

A

●Universal solvent
●High Specific heat capacity
●High latent heat by vaporisation
●Surface Tension
●Strong cohesion between molecules

25
Q

Explain why water is significant to living organisms?

A

●Solvent for polar molecules during metabolic reactions
●Buffer to temperature change
●Strong cohesion of water molecules allows water to move in a column in the transpiration stream

26
Q

What are inorganic ions, and where are they found in the body?

A

●ions that don’t contain a carbon atom
●Found in cytoplasm

27
Q

Explain the role of hydrogen ions in the body.

A

●High concentration of H+= low(acidic) pH
●H+ ions interact with H-bonds and ionic bonds in the tertiary structure of proteins, which cause them to denature

28
Q

Explain the role of iron ions in the body?

A

Fe2+ bonds to porphyrin ring to form haem group in haemoglobin
Haem group has binding sites to transport 1 molecule of O2

29
Q

Explain the role of sodium ions in the body?

A

Involved in co-transport for absorption of glucose and amino acids in small intestine

30
Q

Explain the role of phosphate ions in the body?

A

Component of:
●DNA
●ATP

31
Q

Whats the general structure of an amino acid?

A

-COOH carboxyl group
-R variable “R” group
-NH2 amine group

32
Q

Describe how to test for proteins in a sample

A

Biuret test
1) Add equal volumes of sodium hydroxide to a sample at room temperature
2) Add drops of dilute(II) sulfate solution. Swirl to mix
3) positive result: colour changes from blue to purple
Negative result: The solution remains blue

33
Q

How many different amino acids are there, and how do they differ from each other?

A

20
Differ only by the “R” group

34
Q

How do dipeptides and polypeptides from?

A

●condensation reaction forms peptide bond
●Dipepetides: 2 amino acids
●Polypeptides: 3 or more amino acids

35
Q

How many levels of protein structure are there?

A

4

36
Q

Whats the ‘primary structure’ of a protein

A

Sequence of amino acids in the polypeptide

37
Q

What’s the ‘secondary structure’ of a protein?

A

Folding of the polypeptide chain into a Alpha helix or Beta pleated sheet which is determined by hydrogen bonds

38
Q

Whats the ‘tertiary structure’ of a protein

A

Further folding of the polypeptide chain into its unique 3D shape this is determined by disulfide bridges, ionic bonds, hydrogen bonds

39
Q

What’s the ‘quaternary structure’ of a protein?

A

●Functional proteins may consist of more than one polypeptide
●May involve the addition of prosthetic groups

40
Q

Describe the structure and function of globular proteins

A

●Spherical and compact
●Hydrophilic R groups face outwards and hydrophobic R groups face inwards= usually water-soluble

41
Q

Describe the structure and functions of fibrous proteins

A

●can form long chains or fibres
●Insoluble in water
● useful for structure and support e.g. collagen in skin

42
Q

What are enzymes?

A

Biological catalysts speed up the rate of a reaction by providing an alternative pathway for reactants with a lower activation energy

43
Q

Explain the Induced fit model of enzyme action

A

●shape of active site is not directly complementary to substrate and is flexible
● this causes temporary hydrogen bonds to form, forming a ES complex
●this puts strain on substrate bonds, lowering activation energy

44
Q

How have models of enzymes action changed?

A

●initially lock and key model:rigid shape of active site complementary to only 1 substrate
●currently induced fit model: also explains why binding at allosteric sites can change shape of active site

45
Q

Name 5 factors that affect the rate of enzyme-controlled reactions.

A

●enzyme concentration
●substrate concentration
●concentration of inhibitors
●pH
●temperature

46
Q

How does substrate concentration affect the rate of reaction?

A

Rate of reaction increases proportionally to substrate concentration. However, it levels off when a maximum number of ES complexes form at a give time.

47
Q

How does enzyme concentration affect the rate of reaction?

A

Given that substrate is in excess, rate increases proportionally to enzyme concentration, rate levels off when maximum number of ES complexes form at a given time.

48
Q

How does temperature affect rate of reaction?

A

Rate increases as kinetic energy increases and peaks at optimum temperature.
Above optimum, ionic and H-bonds in tertiary structure=active site no longer complementary to substrate(denaturation)

49
Q

How does pH affect the rate of reaction?

A

Enzymes have a narrow optimum pH range
Outside range, H+/OH- ions interact with hydrogen bond and ionic bonds in tertiary structure.

50
Q

Contrast competitive and non-competitive inhibitors

A

COMPETITIVE INHIBITORS
●similar shape to substrate=binds to active site
●do not stop reaction;ES complexes can still form when inhibitor is released
●increasing substrate concentration decreases their effect
NON-COMPETITIVE INHIBITORS
●bind at allosteric site
●disrupts the tertiary structure, causing enzyme to denature
●increasing substrate concentration has no impact on their effect l

51
Q

How do you calculate the rate of reaction?

A

Change in concentration of product or reactant/time

52
Q

State the formula for pH

A

pH=-log10[H+]

a-level biology (7 decks)

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