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biology > Biological molecules - Proteins > Flashcards

Biological molecules - Proteins Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

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

A
  • 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
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2
Q

what are the two types of proteins

A

fibrous and globular

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3
Q

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

A

50%

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4
Q

what do proteins provide the building materials for

A

growth, repair of tissues and replacement of cells

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5
Q

are proteins polymers

A

yes

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6
Q

how many amino acids are there

A

20

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7
Q

describe how plants get amino acids

A

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

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8
Q

describe how animals get amino acids

A

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

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9
Q

what happens to excess amino acids in animals

A

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

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10
Q

describe the general structure of amino acids

A

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

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11
Q

what does the R group represent

A

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

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12
Q

what is the bond between two amino acids called

A

peptide bond

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13
Q

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

A

form - condensation
breaks - hydrolysis

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14
Q

what is the primary structure

A

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

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15
Q

what determines the primary structure

A

genetic code

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16
Q

where are peptide bonds formed

A

at the ribosome during translation

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17
Q

what is the secondary structure

A

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

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18
Q

what is the secondary structure stabilised by

A

hydrogen bonds

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19
Q

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

A

join helices and sheets together

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20
Q

what is the tertiary structure

A

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

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21
Q

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

A
  • disulfide bonds
  • ionic bonds
  • hydrogen bonds
  • hydrophilic and hydrophobic interactions
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22
Q

do all proteins have a quaternary structure

A

no

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23
Q

when does a protein have a quaternary structure

A

if it is made of two or more polypeptide chains

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24
Q

give examples of proteins with a quaternary structure

A

haemoglobin, collagen

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25
Q

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

A
  • forms between polar groups
  • very weak
  • broken pH and temperature changes
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26
Q

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

A
  • forms between charged groups
  • quite strong
  • broken by pH and temperature changes
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27
Q

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

A

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

28
Q

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

A
  • hydrophobic R-groups (non-polar) point inwards away from water
  • weak
  • broken by changes to the overall 3-D structure (disruption of other bonds)
29
Q

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

A
  • hydrophilic R-groups (polar) point outwards towards water
  • weak
  • broken by changes to the overall 3-D structure (disruption of other bonds)
30
Q

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

A
  • strong covalent bond between amino acids
  • very very strong
  • broken by enzymes e.g pepsin
31
Q

how may a prosthetic group be attached

A

covalent bonds, ionic interactions or hydrogen bonds

32
Q

what are conjugated proteins

A

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

33
Q

give an example of a conjugated protein

A

haemoglobin - haem groups are prosthetic group

34
Q

what are the two types of protein

A

globular and fibrous

35
Q

what is the 3D feature of globular proteins

A

roll up to form balls - spherical

36
Q

what is the 3D feature of fibrous proteins

A

form long, narrow fibres

37
Q

describe the primary structure of globular proteins

A

very precise, usually a non-repeating amino acid sequence

38
Q

describe the primary structure of fibrous proteins

A

often long molecules with simple, repeating amino acid sequence

39
Q

describe the secondary and tertiary structure of globular proteins

A

complex

40
Q

describe the secondary and tertiary structure of fibrous proteins

A

simple

41
Q

describe the solubility in water of globular proteins

A

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

42
Q

describe the solubility in water of fibrous proteins

A

usually insoluble

43
Q

describe the role of globular proteins

A

usually metabolic: enzymes, hormones, transport

44
Q

describe the role of fibrous proteins

A

usually structural

45
Q

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

A

collagen, keratin, elastin

46
Q

where is collagen found

A
  • artery walls
  • tendons
  • bones
  • cartilage
  • skin
47
Q

where is keratin found

A
  • fingernails
  • hair or wool
  • claws and hooves
  • beaks and horns
  • scales and feathers
48
Q

where is elastin found

A
  • skin
  • lungs
  • bladder
  • blood vessels
49
Q

what are the properties and functions of collagen

A

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

50
Q

what are the properties and functions of keratin

A
  • 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
51
Q

what are the properties and functions of elastin

A

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

52
Q

what are the three globular proteins you need to know

A

haemoglobin, insulin and pepsin

53
Q

describe the structure of haemoglobin

A

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)

54
Q

describe the structure of insulin

A

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

55
Q

describe the structure of pepsin

A

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

56
Q

what is the function of haemoglobin

A

carry oxygen from the lungs to tissues

57
Q

what is the function of insulin

A

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

58
Q

what is the function of pepsin

A

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

59
Q

what are computer models used for

A

to predict the structure of proteins

60
Q

what are the advantages of computer modelling

A

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

61
Q

describe the biuret test for proteins, including a positive result

A

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)

62
Q

how does the biuret test work

A

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

63
Q

when may the biuret test not work and why

A

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

64
Q

can insulin change shape

A

no

65
Q

can haemoglobin change shape

A

yes

66
Q

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

A
  • insoluble
  • strong
  • unreactive
67
Q

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

A

different sequence of amino acids therefore R-groups bond differently

biology (24 decks)

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