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A Level Biology: 2.1.2 Biological Molecules > 2.1.2g Proteins > Flashcards

2.1.2g Proteins Flashcards

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1
Q

What are proteins

A

Proteins are polymers

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2
Q

What are the monomers in proteins

A

Amino acids

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3
Q

What is formed when 2 amino acids join together

A

A dipeptide (joined tg by a peptide bond)

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4
Q

What is formed when 2 or more amino acids join together

A

A polypeptide (joined tg by a peptide bond)

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5
Q

What are proteins comprised of

A

Long chains of recurring monomers called amino acids
They are made up of 1 or more polypeptides

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6
Q

Structure of amino acids

A

All amino acids share a common basic structure, with a central CARBON atom bound to:
- An amine group (-NH2) attached to C atom
- A carboxylic acid group (-COOH)
- A hydrogen atom (H)
- A variable side chain (R) (there are 20 diff R groups, therefore there are 20 diff types of amino acids)

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7
Q

See slide 3/5 for diagram of amino acids

A

Practice drawing structure

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8
Q

What is the smallest amino acid

A

Glycine
- the R group is a hydrogen atom
(diagram on slide 5)

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9
Q

What are the bonds between amino acids & how are they joined together

A

Amino acids are covalently joined together in a condensation reaction to form a dipeptide & the release of a water molecule

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10
Q

What is the covalent bond between amino acids called

A

A peptide bond - for this reason, long chains of covalently bonded amino acids are called polypeptides

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11
Q

How can polypeptide chains be broken down

A

Via hydrolysis reactions, which requires water to reverse the process

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12
Q

See slide 7 for diagram of the formation of a dipeptide

A
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13
Q

What are peptide bonds formed between

A

The amine and carboxylic acid groups of adjacent amino acids
This is a C-N bond

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14
Q

How is a water molecule formed in the formation of dipeptides

A

The amine group loses a hydrogen atom (H) & the carboxylic acid loses a hydroxyl (OH) - this forms water (H2O)

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15
Q

What are the levels of protein structure

A
  • PRIMARY structure
  • SECONDARY structure
  • TERTIARY structure
  • QUATERNARY structure
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16
Q

What is the PRIMARY structure of a protein

A
  • This is the order (specific sequence) & number of amino acids in the polypeptide chain
  • The primary structure of protein is determined by the gene
  • Shape of molecule is linear
  • Diff proteins have diff sequences of amino acids in their primary structure. A change in just 1 may change the structure of the whole protein

(see slide 11 for diagram)

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17
Q

What is the SECONDARY structure of a protein

A
  • The polypeptide chain doesnt remain flat/straight. Hydrogen bonds form between nearby amino acids in the chain, making it automatically coil into an alpha helix or beta pleated sheet
  • The secondary structure is the shape that the chain of amino acids forms, either: alpha helix OR beta pleated sheet
  • Both alpha helices & beta pleated sheets result from hydrogen bonds forming between non-adjacent amine & carboxylic group

(see slide 12 for diagram)

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18
Q

What is the TERTIARY structure of a protein

A
  • The coiled or folded chain of amino acids is often coiled and folded further. More bonds form between diff parts of the polypeptide chain.
  • Tertiary structure is the 3D shape of the protein & is formed from further twisting & folding
  • Not all proteins have a tertiary structure

(see slide 13/14)

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19
Q

What are the different bonds that maintain the TERTIARY structure of proteins

A
  • Disulfide bridges: interactions between the sulfur in the R group of amino acid cysteine, these are strong & not easily broken
  • Ionic bonds: form between the carboxyl & amino groups that are not involved in the peptide bond. They are easily broken by pH & are weaker than disulphide bridges
  • Hydrogen bonds: numerous & easily broken
  • Hydrophilic/Hydrophobic interactions
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20
Q

SECONDARY structure of proteins: alpha helix & beta pleated sheets differences

A
  • Alpha helix - STRONG, helical shape
  • Beta pleated sheet - WEAK, strength achieved through layering & bonds between layers
21
Q

How does TERTIARY structure determine function

A

A polypeptide chain will fold differently due to the interactions (& hence the bonds that form) between R groups

Each of the 20 amino acids that make up proteins has a unique R group. Therefore, many different interactions can occur, creating a vast range of protein configurations & therefore functions

22
Q

What is the QUATERNARY structure of a protein

A
  • Some proteins are made of several diff polypeptide chains held tg by bonds. The quaternary structure is the way these polypeptide chains are assembled tg.
  • The quaternary structure is the interaction between 2 or more polypeptides. It is the protein’s final 3D structure
  • This structure only exists in proteins consisting therefore of 2 or more polypeptides

(see s16-17)

23
Q

What is a good example of a protein consisting of 2 or more polypeptides & therefore has a QUATERNARY structure

A

Haemoglobin (Hb, shown on s16)
- Hb becomes a biologically active molecule upon the establishment of it quaternary structure
- Hb is made of 4 polypeptide chains, bonded tg & its role is to carry iron and oxygen around the body
- Hb has a globular quaternary structure

Another eg is collagen - has a fibrous quaternary structure

24
Q

See slide 18 for comparison between primary, secondary, tertiary

A
25
Q

Protein folding

A

Primary –> secondary –> tertiary –> quaternary

26
Q

See s20-21 for summarised diagrams of primary, secondary, tertiary, quaternary

A
27
Q

Bonds of primary structure

A

held tg by the peptide bonds between amino acids

28
Q

Bonds of secondary structure

A

held tg by hydrogen bonds

29
Q

Bonds of tertiary structure

A

this is affected by a few different kinds of bonds

30
Q

What are ionic bonds

A

These are attractions between negatively-charged R groups & positively-charged R groups on different parts of the molecule

31
Q

Describe hydrophobic and hydrophilic interactions

A

When hydrophobic (water-repelling) R groups are close tg in the protein, they tend to clump together. This means that hydrophilic (water-attracting) R groups are more likely to be pushed to the outside, which affects how the protein folds up into its final structure

32
Q

What are hydrogen bonds

A

These weak bonds form between slightly positively-charged hydrogen atoms in some R groups & slightly negatively-charged atoms in other R groups on the polypeptide chain

33
Q

Bonds of quaternary structure

A

this tends to be determined by the tertiary structure of the individual polypeptide chains being bonded tg. Because of this, it can be influenced by all the bonds (peptide, hydrogen, ionic, disulfide)

34
Q

What is a conjugated protein

A

A globular protein that contains a non-protein component called a prosthetic group

There are different kinds of prosthetic groups, they contain an iron ion (Fe2+)

35
Q

What are simple proteins

A

Proteins without a prosthetic group

36
Q

Example of a conjugated protein

A

Haemoglobin

37
Q

Function of haemoglobin

A

Transport of oxygen around the body in the red blood cells

38
Q

Structure of haemoglobin

A

A globular conjugated protein - a protein with a non-protein group attached - a prosthetic group
- Made up of 4 polypeptide chains/subunits (2 alpha, 2 beta…)
- Each of the 4 polypeptide chains has a prosthetic group called Haem
- A Haem group contain iron, which oxygen binds to
- It has hydrophobic R groups on inside, hydrophilic R groups on outside
- Quaternary protein

39
Q

What 2 things can proteins be

A

Globular OR Fibrous

40
Q

What are globular proteins

A

Round and compact
eg. enzymes

41
Q

What are fibrous proteins

A

Composed of long & narrow strands and thus can be used to form fibres for structural roles
eg. keratin

42
Q

Characteristics of globular proteins

A
  • Roll up to form balls
  • Soluble in water
  • Usually have metabolic roles
  • egs. enzymes, haemoglobin
43
Q

Characteristics of fibrous proteins

A
  • Regular, repetitive sequence of amino acids
  • Form fibres
  • Usually insoluble
  • Usually have structural roles
  • egs. collagen, keratin, elastin
44
Q

see slide 27 for comparison between diagram of fibrous and globular

A
45
Q

Collagen

A

A fibrous protein
Properties: strong, tough, insoluble, flexible
Structure: fibrous protein
Function: a connective tissue found in skin, tendons, ligaments & the nervous system
One molecule of collagen is made up of 3 polypeptide chains twisted around eachother in a long, strong rope-like structure

46
Q

Keratin

A
  • Group of fibrous proteins found in skin, hair, nails
  • Contains a large proportion of the sulphur containing amino acid, cysteine
  • This results in the formation of many strong disulphide bonds, forming strong, inflexible, insoluble materials
  • Degree of disulphide bonds determine the flexibility of the protein eg. hair has few disulphide bonds, nails have more
47
Q

Elastin

A

Fibrous protein
- Found in elastic fibres
- Present in the walls of blood vessels & in the alveoli of the lungs
- Elastin gives these structures the flexibility to expand when needed
- Quaternary protein
- Made from many stretchy molecules called, tropelastin

48
Q

Why are globular proteins soluble in water but fibrous proteins are not?

A

Globular proteins have Hydrophobic R groups in the centre of the molecule, not in contact with the water. The Hydrophilic R groups are on the outside of the molecule, in contact w the water. Hydrophilic R groups are attracted to water

Fibrous proteins have Hydrophobic R groups on the outside of the molecule

A Level Biology: 2.1.2 Biological Molecules (13 decks)

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