2.4 Protein

Question 1

Rubisco

Answer 1

• Globular
• Enzyme involved in the fixation of CO2 in chloroplasts

Question 2

Insulin

Answer 2

• Globular
• A hormone involved in regulating blood sugar levels.

Question 3

Immunoglobulin

Answer 3

• Globular
• AKA as antibodies: involved in fighting infections

Question 4

Rhodopsin

Answer 4

• Globular
• A protein linked to pigment, found on the membrane of photoreceptor cells of the retina - allows low light intensities to be detected.
• Allows the retina to be light sensitve

Question 5

Collagen

Answer 5

• Fibrous
• Forms a mesh of fibres in skin and in blood vessel walls that resists tearing.
• A structural protein found in muscles, tendons, and ligaments that provides support and strength.

Question 6

Spider silk

Answer 6

• Fibrous
• A fibrous protein produced by spiders for their webs
• It can be extended and is very resistant to breaking

Question 7

What are proteins made from?

Answer 7

Proteins are organic compounds made from carbon, hydrogen, oxygen and nitrogen. They usually contain sulpur and often phosphorous.

Question 7

What are the monomers of proteins?

Answer 7

Proteins are made from amino acids, of which there are 20 different types.
- Amino acids all have an amino group (NH2) and a carboxyl group (COOH). The also have an R group, this is different in different amino acids.

Question 8

Polypeptides

+where are they made?

Answer 8

Polypeptides are long chains of amino acids. Amino acids can be linked together in any sequence giving a huge range of possible polypeptides.

These are made on the ribosomes.

Question 9

What kind of bond is there between amino acids when a polypeptide is formed?

and what kind of reaction occurs?

Answer 9

Peptide bond.
- Amino acids can be joined together using condensation reactions. The condensation occurs between the amino group from one amino acid
and the carboxyl group from another.

Question 10

Why is the amino acid sequence important? What does it determine?

Answer 10

It determines the three-dimensional conformation of a protein.

Question 11

Primary structure of protein

Answer 11

A polypeptide chain

Question 12

Secondary structure of protein

Answer 12

Occurs when a hydrogen bond is formed between a hydrogen in the amine group of one amino acide and an oxygen in the carboxyl group of another amino acid
Includes: alpha helix and beta pleated sheet
- Depends on how the bonds are oriented

Question 13

Tertiary structure of protein

Answer 13

The polypeptide folds and coils to form a complex 3D shape
The tertiary structure is a result of interactions between R groups through:
- Hydrophobic interactions
- Hydrogen bonds
- Ionic bonds between positively and negatively charged side chains
- Disulfide Bridges

Note: for proteins such as enzymes this is the final shape of the molecule

Question 14

Quaternary structure of protein

Answer 14

The interaction between multiple polypeptides or prosthetic groups.
Note: a prosthetic group is an inorganic compound involved in a protein (e.g. the heme group in
haemoglobin)
Haemoglobin is made of 4 polypeptide chains + the haeme groups

Question 15

Denaturation

Answer 15

A structural change in a protein that results in the loss (usually permanent) of its biological properties.
- Because the way a protein folds determines its function, any change or abrogation of the tertiary structure will alter its activity

Question 16

Temperature and denaturation of proteins

Cause of denaturation

Answer 16

• High levels of thermal energy may disrupt the hydrogen bonds that hold the protein together
• As these bonds are broken, the protein will begin to unfold and lose its capacity to function as intended
• Temperatures at which proteins denature may vary, but most human proteins function optimally at body temperature (~37ºC)

Question 17

pH and denaturation of proteins

Cause of denaturation

Answer 17

• Changing the pH will alter the charge of the protein, which in turn will alter protein solubility and overall shape
• All proteins have an optimal pH which is dependent on the environment in which it functions (e.g. stomach proteins require an acidic environment to operate, whereas blood proteins function best at a neutral pH)

Question 18

What codes the amino acid sequence for polypeptides?

Answer 18

Genes

Question 19

How do genes code for the amino acid sequences of polypeptides?

Answer 19

A gene is a sequence of DNA which encodes a polypeptide sequence
A gene sequence is converted into a polypeptide sequence via two processes:
- Transcription – making an mRNA transcript based on a DNA template (occurs within the nucleus)
- Translation – using the instructions of the mRNA transcript to link amino acids together (occurs at the ribosome)

Question 20

Proteome

Answer 20

The totality of proteins expressed within a cell, tissue or organism at a certain time.
- The proteome of any given individual will be unique, as protein expression patterns are determined by an individual’s genes

The proteome is always significantly larger than the number of genes in an individual due to a number of factors:
- Not all genes produce polypeptides.
- Gene sequences may be alternatively spliced following transcription to generate multiple protein variants from a single gene
- Proteins may be modified (e.g. glycosylated, phosphorylated, etc.) following translation to promote further variations

Question 21

Functions of proteins

Answer 21

Structural proteins - collagen, spider silk
Enzymes - rubisco
Hormones - insulin
Immunoglobin - antibodies
Gas transport - haemoglobin
Sensitivity/receptor - rhodopsin