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Biology AS > Biological Molecules > Flashcards

Biological Molecules Flashcards

1
Q

What are 4 roles of water in living organisms and what properties make it ideal for them?

A
  1. Acts as a transport medium (e.g. blood plasma) - solvent properties and high viscosity
  2. Acts as a thermal buffer in enzyme reactions as it heats up and cools down slowly thanks to hydrogen bonds
  3. Ice insulates water allowing aquatic organisms to survive during cold months - hydrogen bonds mean ice is less dense than water
  4. Solvent for many organic molecules e.g.. monosaccharides, disaccharides, glycerol, fatty acids, amino acids, and inorganic molecules e.g. Na+ ions, allowing DIFFUSION of materials through membranes
  5. Determines membrane structure - phospholipids form a bilayer due to hydrophobic tails and hydrophilic heads
  6. Latent heat of vaporisation - acts as a coolant for the body as water is evaporated in sweat, using heat energy
  7. Surface tension due to H bonding - allows small organisms to walk on it
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2
Q

How are proteins amphoteric?

A

they can act as acids or bases:
The amine group, NH2, can accept H+ to becomes NH3+ (basic)
The carboxylic acid group, COOH, can donate H+ to become COO- (acidic)

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3
Q

How are peptide bonds made between amino acids? and broken?

A

made by condensation reactions, broken by hydrolysis

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4
Q

What is primary structure of proteins?

A

The sequence & types of amino acids present in the polypeptide chain - determined by the genetic code of the DNA

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5
Q

What is secondary structure of proteins?

A

The coiling/folding of the polypeptide chain due to hydrogen bonding between amino acids and carboxyl groups. Results in 2 types of secondary structure: alpha helix and beta pleated sheet

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6
Q

What is tertiary structure in proteins?

A

Further coiling/folding of the polypeptide chain due to bonds between R groups of amino acids. Bonds are:
H bonds between OH/NH groups and CO groups
Disulphide bonds
Ionic bonds
Hydrophobic and hydrophilic interactions

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7
Q

What are three differences between globular and fibrous proteins? example of each?

A
  1. tertiary structure: G = spherical, F = linear
  2. solubility in water: G = soluble (hydrophobic amino acids in the centre) F = insoluble (hydrophobic amino acids exposed)
  3. function: G = mainly metabolic functions, F = mainly structural functions
  4. Primary structure: G = irregular, F = repeated amino acid sequences
    E.g. haemoglobin is globular, collagen is fibrous
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8
Q

When do proteins have quaternary structure?

A

when 2 or more polypeptide chains are linked together

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9
Q

What is the general formula of a carbohydrate?

A

Cx(H2O)y

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10
Q

How do alpha and beta glucose differ?

A

in alpha glucose the OH group on C1 is below the ring and in beta glucose it is above

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11
Q

cellulose has what kind of glucose as a component?

A

beta glucose

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12
Q

starch/glycogen have what kind of glucose a s a component?

A

alpha glucose

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13
Q

What are 3 functions of glucose?

A
  1. Main respiratory substrate (broken down to form ATP energy)
  2. soluble, dissolves in water and is transported in the blood and can diffuse into cells
  3. Used to form other carbohydrates through condensation reactions
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14
Q

What kind of bonds form when 2 glucose units link together? what kind of saccharide is this

A

glycosidic link

dissachharide = 2 monosaccharides linked

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15
Q

How are glycosidic bonds broken?

A

by hydrolysis

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16
Q

How are polysaccharides formed?

A

by repeated condensation reactions between glucose units

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17
Q

What are 3 functions of starch?

A
  1. Good energy source thanks to many chemical bonds and H atoms
  2. main storage carbohydrate of plants - in chloroplasts
  3. Insoluble, so can’t diffuse out of cell and has no effect on the water potential of the cell
  4. Compact structure thanks to helical shape, so takes up less space in the cell
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18
Q

Functions of glycogen?

A

main storage carbohydrate of animal cells

same properties as starch, except it forms more compact granules within the cytoplasm due to its branched structure

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19
Q

3 functions of cellulose?

A
  1. Main structural component of plant cell walls
  2. freely permeable to water and solutes
  3. strong due to many cellulose molecules being linked together in fibres
  4. rigid with limited expansion to prevent plant cells bursting die to water entry by osmosis
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20
Q

Describe the difference between starch(amylose), glycogen and cellulose chains

A

Starch: coiled, unbranched chains
Cellulose: straight, unbranched chains
Glycogen: branched chain with 1-6 glycoside bonds at the branches and 1-4 glycosidic bonds within the chains

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21
Q

Composition of triglycerides?

A

3 fatty acid tails and one unit of glycerol, joined together during condensation reactions to form ester bonds

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22
Q

3 functions of triglycerides?

A
  1. act as long term energy stores: contain C-H bonds so a lot of energy
  2. insoluble (as long as the long hydrocarbon chain is hydrophobic), so do not affect the water potential
  3. insoluble so cannot diffuse out of cells
  4. relatively easily hydrolysed into fatty acids and glycerol for respiration when required
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23
Q

What are phospholipids made up of

A

2 fatty acids, a unit of glycerol and a phosphate group joined via condensation reactions
Heads: glycerol and phosphate, hydrophilic
Tails: 2 fatty acids, hydrophobic

24
Q

3 functions of phospholipids?

A
  1. Component of cell membrane
  2. Barriers to polar molecules and ions due to hydrophobic tails
  3. allow non-polar molecules to pass
  4. form a bilayer
25
Q

What type of lipid is cholesterol?

A

steroid

26
Q

What is the role of cholesterol in cell membranes?

A

regulates fluidity - makes it more stable

27
Q

Test for proteins? what would you see if protein is present

A
  • Mix test solution with excess NaOH
  • Trickle dilute copper sulphate down the side of the tube
  • dark blue ring forms on surface and turns purple on careful shaking
28
Q

Test for reducing sugars? and conc?

A
  • heat equal quantitys of test solution + benedict’s reagent to 80 degrees for 5 mins
  • benedict’s regent is reduced from a blue colour (CuSO4) to green/brown/brick red (CuO) depending on the concentration of reducing sugars present
  • colour change can be measured using a colorimeter - more glucose = more light absorbed due to more brick red precipitate
29
Q

Test for non-reducing sugars?

A
  • Boil test solution with a few drops of HCl to hydrolyse any disaccharides to monosaccharides
  • neutralise with NaOH (benedicts doesn’t work at an acid pH)
  • repeat benedicts test as you would with reducing sugar test
30
Q

Test for starch?

A

Iodine regent, yellow-brown –> blue-black precipitate when starch is present

31
Q

Test for lipids?

A
  • equal quantities of test solution and ethanol mixed together
  • mixture allowed to separate into 2 layers
  • some of the upper layer is poured into a tube of water
  • a cloudy emulsion is formed if lipid is present
32
Q

what are the three components making up a nucleotide?

A
  • a phosphate group
  • a pentose sugar
  • a nitrogenous base
33
Q

Which 2 bases are purines and what is meant by this?

A

Adenine and Guanine

large, double ring structures, bond with pyrimidines

34
Q

Which 3 bases are pyrimidines and what is meant by this?

A

Thymine and Cytosine and Uracil

small, single ring structures, bond with purines

35
Q

Why are the 2 polynucleotide chains making up DNA equidistant?

A

because of complementary base pairing - a large purine always pairs opposite a small pyrimidine

36
Q

structure of haemoglobin related to function?

A
  • conjugated protein with 4 prosthetic harm groups containing iron to bind with oxygen
  • quaternary structure of 2 alpha and 2 beta chains
  • globular tertiary structure = compact, and water soluble so can dissolve in the cytoplasm
  • mostly alpha helix secondary structure = compact
37
Q

structure of collagen related to function?

A
  • primary structure where every third amino acid is glycine meaning it can make many hydrogen bonds = strong
  • strong regular alpha helix secondary structure held together by hydrogen bonds
  • fibrous tertiary structure - insoluble as hydrophobic amino acids are exposed. Insolubility is vital for its structural role.
  • quaternary structure of 3 polypeptide chains wound around each other and held together by hydrogen bonds = very strong. Left-handed helix.
  • adjacent molecules joined by covalent crosslinks
  • fibril
38
Q

describe the structure of RNA in comparison to DNA

A

RNA is a single stranded polynucleotide containing bases adenine, guanine, cytosine and uracil only, whereas DNA is a double stranded polynucleotide containing bases A T and C G with the 2 chains anti-parallel and twisted into a double-helix.

39
Q

In which phase of the cell cycle does DNA replication occur?

A

interphase

40
Q

Describe the steps of DNA replication

A
  1. DNA unzips and unwinds as the H bonds between complementary base pairs are broken
  2. Free DNA nucleotides pair up with the exposed bases on the original/template DNA chains and form new H bonds with them. Adjacent new nucleotides are joined together by condensation reactions to form new sugar-phosphate backbones.Catalysed by DNA polymerase.
  3. 2 identical DNA molecules are made each consisting of one original and one new chain of nucleotides - semi-conservative replication
    The two identical DNA molecules firm the 2 chromatids of a chromosome that are visible during mitosis and meiosis
41
Q

what is a gene?

A

a sequence of DNA nucleotides that codes for a polypeptide

42
Q

describe the roles of DNA and RNA

A

DNA:
Genetic code of the cell, provides the instructions for making new proteins. A gene codes for the polypeptides which make up a protein.
RNA:
protein synthesis - the base sequence of DNA is copied to make a complementary sequence of bases in RNA. RNA molecule leaves the nucleus and goes to the ribosomes where the proteins are assembled.

43
Q

what are enzymes?

A

globular proteins, with a specific tertiary structure, which catalyse metabolic reactions in living organisms

44
Q

Describe how enzymes lower the activation energy of a reaction

A

they attract substrates in a precise orientation that makes it more likely for bonds to form or be broken. They do this by having an active site which is complementary in shape to a specific substrate and usually has an opposite charge so that H bonds can be formed between enzyme and substrate. Each enzyme is specific

45
Q

enzyme action may be intracellular or extracellular. What is meant by this? e.g.?

A

extracelllular enzymes - secreted by cells and work outside, e.g. digestive enzymes in the gut lumen
intracellular enzymes - work within a cell e.g. lysins in lysosomes

46
Q

describe the lock and key hypothesis to explain the method of action of enzymes? and the induced-fit hypothesis

A

Lock and key: the enzymes active site is of the correct shape for specific substrates to fit it forming an enzyme-substrate complex
Induced fit: The shape of an enzymes active site is caused by the arrival of a specific substrate which induces/stimulates an exact fit to form and enzyme-substrate complex.

47
Q

Describe the effect of temperature on enzyme activity

A

Increased temp. increases rate of reaction up to the optimum temperature due to the uncreased kinetic energy causing increased enzyme-substrate collisions and so more enzyme-substrate complexes. Human enzymes optimum = 37degrees, plants = 20degreesish. Beyond the optimum temp. the rate of reaction decreases rapidly due to excessive kinetic energy causing bonds to vibrate and unravelling the tertiary structure meaning active site is lost and enzymes is denatured. Irreversible.

48
Q

Describe the effect of pH on enzyme activity

A

Each enzyme has its optimum pH where the reaction rate is fastest. Slight changes in pH either side of the optimum slow down the reaction rate as the active site and substrates can have the same charge, so repel each other. More severe changes in pH denature enzymes by disrupting bonds holding together tertiary structure so active site is lost.

49
Q

Describe the effect of substrate concentration on enzyme activity

A

When at a fixed, low conc. of enzyme, the rate of reaction increases initially as substrate conc. increases due to an increased chance if enzyme-substrate collisions. Eventually the rate of reaction remains constant as all enzyme active sites are occupied and the enzymes are working at their maximum rate.

50
Q

Describe the effect of increased enzyme concentration on enzyme activity

A

with excess substrate, this will increase the rate of reaction, with the reaction rate directly proportional to enzyme conc due to increased chance of enzyme-substrate collisions and more active sites available.

51
Q

explain the effects of competitive inhibitors on the rate of enzyme-controlled reactions. What does the degree of inhibition depend on?

A

Have very similar structures to the substrate so inhibit enzymes by entering the active site and so preventing the substrate from entering. The degree of inhibition depends on the relative concentrations of substrate and inhibitor - more substrate = less inhibition.

52
Q

explain the effects of non- competitive inhibitors on the rate of enzyme-controlled reactions.

A

Inhibitor does not fit into the active site, but bonds to the enzyme elsewhere, distorting its tertiary structure and usually denaturing the enzyme. Slow down the rate of reaction no mater how much substrate is present.

53
Q

Describe the difference between reversible and irreversible non-competitive inhibitors.

A

Reversible - bind temporarily to the enzymee.

Irreversible - bind permanently to the enzyme

54
Q

What are cofactors and coenzymes?

A

Needed for enzymes to work.
Cofactors- present to ensure enzyme-controlled reactions take place
Coenzymes- type of cofactor, organic molecules which bind for a short time to the active site making it easier for the substrate to fit into the active site. Are changed in some way but can be recycled

55
Q

describe the action of one named poison that is an enzyme inhibitor

A

the metabolic poison alpha-amantin from death cap mushrooms binds to enzymes that produce RNA from DNA stopping cells synthesising proteins. Non-competitive inhibitor, irreversible.

56
Q

describe a medicinal drug that works by inhibiting the activity of enzymes

A

medicinal drug digitalis binds to ATPase causing increased contraction of heart muscle. Non-competitive inhibitor, reversible.

Biology AS (5 decks)

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