Proteins (page 26 - 28)

Question 1

What are Proteins made from?

Answer 1

from long chains of Amino Acids

There are millions of different proteins. They;re the most abundant (plentyful) molecules in cells, making up 50% or more of a cells dry mass. Like carbohydrates and lipids, proteins are essential for life.

Question 2

Proteins are polymers true or false?

Answer 2

true, just like carbohydrates (see apge 22)

Question 3

What are Amino Acids?

Answer 3

they are the monomers in proteins

Question 4

When is a dipeptide formed?

Answer 4

when two amion acids join together.

Question 5

When is a polypeptide formed?

Answer 5

when more than two amino acids are joined together.

Question 6

Proteins are made up of one or more what?

Answer 6

polypeptides.

Question 7

All amino acids have the same general structure, what group is it called?

Answer 7

a carboxyl group (-COOH) and an amino group (-NH²) attached to a carbon atom. the difference between different amio acids is the variable group (R on diagram 1, page 26) they contain.

different amino acids have different variable groups.

Question 8

All amion acids contain what chemical elements?

Answer 8

carbon, oxygen, hydrogen and nitrogen.

some also contain sulfur.

Question 9

How are amino acids joined together?

Answer 9

they are joined together by Peptide Bonds

to form dipeptides and polypeptides

Question 10

Explain how amion acids are joined together by peptide bonds?

Answer 10

a molecule of water is released during the reaction - it’s a condensation reaction.

Question 11

Explain the amion acids hydrolysis reaction?

Answer 11

its the reverse of the condensation reaction. the reverse adds a molecue of water to break the peptide bond - it’s a hydrolysis reaction.

see structure diagram 2 on page 26.

Question 12

Proteins hav four structural levels, name them?

Answer 12

Primary Structure
Secondary Structure
Tertiary Structure
Quaternary Structure.

Question 13

Proteins are big, complicated molecules. They’re much easier to explain if you describe their structure in four ‘levels’.

Explain the Primary Structure level of Proteins.

Answer 13

this is the sequence of amion acids in the polypeptide chain. Different proteins have different sequences of amion acids in their primary structure. A change in just one amion acid may change the structure of the whole progein.

see diagram 1 on page 27.

Question 14

Explain the secondary Structure level of Proteins?

Answer 14

the polypeptide chain doesn’t remain flat and straight. Hydrogen bonds form between nearby amino acids in the chain. This makes it automatically coil into an alph (a) helix of fold into a beta (β) pleated sheet - this is the secondary structure.

see diagram 2 on page 27

Question 15

Explain the Tertiary Structure level of Proteins?

Answer 15

the coiled or folded chain of amino acids is often coiled and folded further. More bonds form between different parts of the polypeptide chain. For proteins made from a single polypeptide chain, the tertiary structure forms their final 3D structure.

see diagram 3 on page 27

Question 16

Explain the Quaternary Structure level for proteins?

Answer 16

some proteins are made of several different polypeptide chains held together by bonds. The quaternary structure is the way these polypeptide chains are assembled together. E.g. haemoglobin is made of four polypeptide chains, bonded together. For progeins made from more than one polypeptide chain, the quaternary structure is the proteins final 3D structure.

see diagram 4 on page 27.

(computer modelling can create 3D interactive images of proteins. this is really handy for investigating the different levels of structure in a protein molecule).

Question 17

Different Bonds hold different structural levels together.

The four structural levels of a protein are held together by what bonds?

Answer 17

different kinds of bonds.

Question 18

How is the Primary Structure of a protein held together?

Answer 18

by the peptide bonds between amion acids

Question 19

How is the Secondary Structure of a protein held together?

Answer 19

by hydrogen bonds

Question 20

How is Tertiary Structure proteins held together

Answer 20

this is affected by a few different kind of bonds:

Ionic Bonds
Disulfide Bonds
Hydrophobic and Hydrophillic interactions
Hydrogen Bonds

Question 21

How is Quarternary Structure of protein held together?

Answer 21

this tends to be dtermined by the tertiary structure of the individual polypeptid chains being bonded together. because of this, it can be influenced by all the bonds (primary, secondary, tertiary).

Question 22

Tertiary Structure bond of a protein is affected by

Ionic Bonds, explain why?

Answer 22

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

Question 23

Tertiary Structure bond of a protein is affected by

Disulfide Bonds, explain why?

Answer 23

whenever two molecules of the amion acid cysteine com close together, the sulfur atom in one cysteine bonds to the sulfur in the other cysteine, forming a disulfide bond.

Question 24

Tertiary Structure bond of a protein is affected by

Hydrophobic and Hydrophillic interactions, why?

Answer 24

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

Question 25

Tertiary Structure bond of a protein is affected by

Hydrogen Bonds, why?

Answer 25

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

Question 26

what will happen if you heat a protein to a high temperature?

Answer 26

it will break up its ionic and hydrophobic/hydrophilic interactions and hydrogen bonds. In turn this will cause a change in the proteins 3D shape.

Question 27

In a globular protein, the hydrophillic R groups on the amino acids tend to be pushed to the outside of the molecule, what is the cause of this?

Answer 27

it is caused by hydrophobic and hydrophillic interactions in the proteins tertiary structure (see previous page).

This makes globular proteins soluble, so they’re easily transported in fluids.

Question 28

Globular proteins have a range of functions in living organisms, give some examples?

Answer 28

Haemoglobin
Insulin
Amylase

Question 29

What are Globular Proteins?

Answer 29

they are round structures, like their name, globular proteins have a round, spherical formation. This is because the hydrophobic parts of the protein fold inwards while the hydrophillic parts become arranged around the external surface. Globular proteins are water soluble.

Question 30

What is Haemoglobin?

Answer 30

Haemoglobin is a globular protein that carries oxygen around the body in red blood cells (see page 86)

It’s known as a conjugated protein - this means its a protein with a non-protein group attached.

The non- protein part is called a prosthetic group.

Each of the four polypeptide chains in haemoglobin has a prosthetic group called haem.

A haeman group contains iron, which oxygen binds too. (see diagram 1, page 28 of a haem group).

Question 31

What is Insulin?

Answer 31

Insulin is a hormone secreted by the pancreas. It helps to regulate the blood glucose level.

Its solubility is important - it means it can be transported in the blood to the tissues where it acts.

An insulin molecule consists of two polypeptide chains, which are held together by disulfide bonds.

Question 32

What is Amylase?

Answer 32

It is an enzyme (see page 42), that catalyses the breakdown of starch in the digestive system.

It is made of a single chain of amion acids.

Its secondary structure contains both alpha-helix and beta-pleated sheet sections.

Most enzymes are globular proteins.

Question 33

What are Fibrous Proteins?

Answer 33

They are tough and Rope-shaped proteins.

They are insoluble and strong.

They’re structural proteins and are fairly unreactive (unlike many globular proteins).

Question 34

Name 3 Fibrous Proteins? (you need to know these)

Answer 34

Collagen
Keratin
Elastin

Question 35

What is Collagen?

Answer 35

Collagen is a Fibrouse Protein, found in animal connective tissure, such as bone, skin and muscle. It is a very strong molecule. Minerals can bind to the protein to increase its rigidity, e.g. in bone. See diagram 2 on page 28 of the structure of a collagen molecule).

Question 36

What is Keratin?

Answer 36

Keratin is a Fibrouse Protein, found in many of the external structures of animals, such as skin, hair nails, feathers and horns. It can either be flexible (as it is in skin) or hard and touch (as it is in nails).

Question 37

What is Elastin?

Answer 37

Elastin is a Fibrous Protein, found in the elastic connective tissue, such as skin, large blood vessels and some ligaments. It is elastic, so it allows tissues to return to their original shape after they have been stretched.

Question 38

Describe the general structure of an amion acid?

Answer 38

Amion acids have two different functional groups attached to a chiral carbon, a carboxylic acid group (-COOH) and an amine group (-NH²). They also have an ‘R; group which is the variable group, this is different for each amino acid. All amion acids, except glycine, contain a chiral carbon atom.

Question 39

Name the bond that joins amino acids together in proteins?

Answer 39

Peptide Bondinig.
Proteins are formed when amino acids become linked to each other via peptid bonds. Condensation reactions join amino acids. Condensation reactions lead to formation of strong covalent bonds called peptide bonds, which hold the amino acids together.

Question 40

What is a conjugated protein?

Answer 40

A conjugated protein is defined as a protein to which another chemical group (e.g, carbohydrate), is attached either covalent bonding or interactions.

Question 41

Suggest which of the following proteins is most abundant in a tortoise’s shell?

a) Collagen
b) Elastin
c) Alpha-amylase
d) Keratin (1 mark)

Answer 41

Keratin (1 mark)

Question 42

HSA is a globular protein, which transports other molecules such as fatty acids around the bloodstream. The molecule consists of 585 amion acids, several of which are cysteine. Describe the bonds that could be present in the tertiary structure of HSA and suggest how its structure makes it suited for its role of transporting molecules in the blood (6 marks)

(you will be assessed on the quality of your written response in this question).

Answer 42

5-6 marks:
The answer fully describes four different bonds that may be in the tertiary structure and explains clearly how the structure of HSA makes it suited to its role. The answer has a clear and logical structure. The information given is relevent and detailed.

3-4 marks:

The answer describes two of three of the bonds that may be in the teritary scructure and explains briefly how the structure of HSA makes it suited to its role. The answer has some structure. Most of the information given is relevant and there is some detail involved.

1-2 marks:
The answer briefly describes on of the bonds that may be in the tertiary strcuture and there is an attempt to link the structure of HSA to its role. The answer has no clear structure. Theinformation given is basic and lacking in detail. It may not be relevant.

0 marks:
No relevant information is given.

Here are some points your answer may include:
The tertiary structure may contain ionic bonds. These are attractions between negatively-charged R groups. and positively-charged R groups on different parts of the molecule. It may also contain disulfide bonds, which form when the sulfur atoms in two nearby cysteine molecules bond. There may also be hydrogen bonds, which are weak bonds between slightly positively-charged hydrogen atoms in some R groups, and slightly negatively-charged atoms in other R groups on the polypeptide chain. The tertiary structure will also contain hydrophobic and hydrophillic interactions. Hydrophobic R groups clump together meaning that hydrophillic R groups are more likely to be pushed to the outside. This will make HSA soluble in water, which makes it suited for its role of transporting molecules in the blood.