Biological molecules - Proteins

Question 1

giving examples where necessary, what are the roles of proteins in organisms (8 things)

Answer 1

• cell signalling molecules e.g hormones such as insulin
• transport oxygen in red blood cells e.g haemoglobin
• antibodies - fight pathogens
• structural - build cells
• enzymes e.g pepsin, speeding up metabolic reactions
• muscles and contraction e.g actin and myosin
• receptors on surface of membrane
• membrane carriers and channels

Question 2

what are the two types of proteins

Answer 2

fibrous and globular

Question 3

what percentage of the organic matter of the cell do proteins make up

Answer 3

50%

Question 4

what do proteins provide the building materials for

Answer 4

growth, repair of tissues and replacement of cells

Question 5

are proteins polymers

Answer 5

yes

Question 6

how many amino acids are there

Answer 6

20

Question 7

describe how plants get amino acids

Answer 7

plants can make all the amino acids they need - but they need a source of nitrogen. they get this from nitrates in the soil

Question 8

describe how animals get amino acids

Answer 8

animals can make some amino acids, but must ingest and absorb others (essential amino acids)

Question 9

what happens to excess amino acids in animals

Answer 9

they cannot be stored so are broken down in the liver to urea and excreted by the kidney

Question 10

describe the general structure of amino acids

Answer 10

C-C-N backbone with an amino group at one end and a carboxyl group at the other, with an R group and hydrogen attached to the central C

Question 11

what does the R group represent

Answer 11

any one of 20 possible groups, which determine what particular amino acid it is

Question 12

what is the bond between two amino acids called

Answer 12

peptide bond

Question 13

what type of reaction forms and breaks the bond between two amino acids

Answer 13

form - condensation
breaks - hydrolysis

Question 14

what is the primary structure

Answer 14

the specific sequence of amino acids forming a chain of amino acids joined by peptide bonds

Question 15

what determines the primary structure

Answer 15

genetic code

Question 16

where are peptide bonds formed

Answer 16

at the ribosome during translation

Question 17

what is the secondary structure

Answer 17

how a polypeptide folds. it forms one of two structures - alpha helix or beta pleated sheet

Question 18

what is the secondary structure stabilised by

Answer 18

hydrogen bonds

Question 19

what do parts of the polypeptide that have no secondary structure do

Answer 19

join helices and sheets together

Question 20

what is the tertiary structure

Answer 20

the 3D shape of a protein determined by the way that alpha helices and beta pleated sheets interact with one another

Question 21

what are four main types of bond/interaction that hold together the tertiary structure

Answer 21

• disulfide bonds
• ionic bonds
• hydrogen bonds
• hydrophilic and hydrophobic interactions

Question 22

do all proteins have a quaternary structure

Answer 22

no

Question 23

when does a protein have a quaternary structure

Answer 23

if it is made of two or more polypeptide chains

Question 24

give examples of proteins with a quaternary structure

Answer 24

haemoglobin, collagen

Question 25

describe hydrogen bonds in proteins (how does it form, strength and what is it broken by)

Answer 25

- forms between polar groups - very weak - broken pH and temperature changes

Question 26

describe ionic bonds in proteins (how does it form, strength and what is it broken by)

Answer 26

- forms between charged groups - quite strong - broken by pH and temperature changes

Question 27

describe disulfide bonds in proteins (how does it form, strength and what is it broken by)

Answer 27

forms between sulphur atoms in the R-groups (e.g cysteine), very strong, broken by reducing agents e.g strong acids

Question 28

describe hydrophobic bonds in proteins (how does it form, strength and what is it broken by)

Answer 28

- hydrophobic R-groups (non-polar) point inwards away from water - weak - broken by changes to the overall 3-D structure (disruption of other bonds)

Question 29

describe hydrophilic bonds in proteins (how does it form, strength and what is it broken by)

Answer 29

- hydrophilic R-groups (polar) point outwards towards water - weak - broken by changes to the overall 3-D structure (disruption of other bonds)

Question 30

describe peptide bonds in proteins (how does it form, strength and what is it broken by)

Answer 30

- strong covalent bond between amino acids - very very strong - broken by enzymes e.g pepsin

Question 31

how may a prosthetic group be attached

Answer 31

covalent bonds, ionic interactions or hydrogen bonds

Question 32

what are conjugated proteins

Answer 32

proteins that contain a non-protein part. this part is known as a prosthetic group

Question 33

give an example of a conjugated protein

Answer 33

haemoglobin - haem groups are prosthetic group

Question 34

what are the two types of protein

Answer 34

globular and fibrous

Question 35

what is the 3D feature of globular proteins

Answer 35

roll up to form balls - spherical

Question 36

what is the 3D feature of fibrous proteins

Answer 36

form long, narrow fibres

Question 37

describe the primary structure of globular proteins

Answer 37

very precise, usually a non-repeating amino acid sequence

Question 38

describe the primary structure of fibrous proteins

Answer 38

often long molecules with simple, repeating amino acid sequence

Question 39

describe the secondary and tertiary structure of globular proteins

Answer 39

complex

Question 40

describe the secondary and tertiary structure of fibrous proteins

Answer 40

simple

Question 41

describe the solubility in water of globular proteins

Answer 41

usually soluble - hydrophilic R groups on outside and in contact with water

Question 42

describe the solubility in water of fibrous proteins

Answer 42

usually insoluble

Question 43

describe the role of globular proteins

Answer 43

usually metabolic: enzymes, hormones, transport

Question 44

describe the role of fibrous proteins

Answer 44

usually structural

Question 45

what are the three examples of fibrous proteins you need to know

Answer 45

collagen, keratin, elastin

Question 46

where is collagen found

Answer 46

- artery walls - tendons - bones - cartilage - skin

Question 47

where is keratin found

Answer 47

- fingernails - hair or wool - claws and hooves - beaks and horns - scales and feathers

Question 48

where is elastin found

Answer 48

- skin - lungs - bladder - blood vessels

Question 49

what are the properties and functions of collagen

Answer 49

strong and inelastic, providing internal mechanical strength e.g prevents bursting

Question 50

what are the properties and functions of keratin

Answer 50

- lots of the amino acid cysteine in the polypeptide so lots of disulfide bonds form between chains. - provides mechanical protection as it is a very strong and hard molecule - also acts as a waterproof and impermeable barrier

Question 51

what are the properties and functions of elastin

Answer 51

due to cross-linking and coiling it is strong and extensible, allowing things to stretch or adapt their shape

Question 52

what are the three globular proteins you need to know

Answer 52

haemoglobin, insulin and pepsin

Question 53

describe the structure of haemoglobin

Answer 53

a conjugated protein as it contains non-protein prosthetic haem groups which contain Fe2+ which bonds to oxygen. it has four polypeptides in its quaternary structure (2 alpha and 2 beta)

Question 54

describe the structure of insulin

Answer 54

2 polypeptide chains A begins with an alpha helix B ends with a beta pleated sheet each forms its own tertiary structure - joined by disulfide bonds

Question 55

describe the structure of pepsin

Answer 55

no quaternary structure 1 polypeptide chain that folds into a symmetrical tertiary structure of 327 amino acids, only 4 have basic R groups - gives stability in low pH environment

Question 56

what is the function of haemoglobin

Answer 56

carry oxygen from the lungs to tissues

Question 57

what is the function of insulin

Answer 57

hormone - binds to glycoprotein receptors on muscle and fat cells to: increase rate of glucose uptake from blood, increase rate of glucose consumption

Question 58

what is the function of pepsin

Answer 58

enzyme - digests protein in the stomach (breaks peptide bonds)

Question 59

what are computer models used for

Answer 59

to predict the structure of proteins

Question 60

what are the advantages of computer modelling

Answer 60

fast, smaller research teams, cheaper, gives an indication of whether an interaction would work

Question 61

describe the biuret test for proteins, including a positive result

Answer 61

mix 1cm cubed of suspension or solution with an equal volume of biuret reagent. swirl the tube and look for a colour change (blue to lilac)

Question 62

how does the biuret test work

Answer 62

the chemicals in the biuret solution react with the peptide bonds in a protein

Question 63

when may the biuret test not work and why

Answer 63

it will not go lilac with just a mixture of amino acids, as it only detects the presence of proteins because of peptide bonds

Question 64

can insulin change shape

Answer 64

no

Question 65

can haemoglobin change shape

Answer 65

yes

Question 66

state three properties of a fibrous protein that are different to those of a globular protein

Answer 66

- insoluble - strong - unreactive

Question 67

two proteins have the same number and type of amino acids but different tertiary structures. why

Answer 67

different sequence of amino acids therefore R-groups bond differently

Question 68

state the properties of collagen that make it suitable for the function of ligaments

Answer 68

- high tensile strength - resistant to stretching - fibrous - insoluble

Question 69

describe and explain why collagen is a fibrous protein

Answer 69

- long chain - little/no tertiary structure - structural function - insoluble

Question 70

suggest why collagen is such a strong molecule

Answer 70

many hydrogen bonds between polypeptides