Proteins

Question 1

Proteome

Answer 1

The entire set of proteins expressed by a genome

Question 2

The proteome is larger than the number of genes because…?

Answer 2

more than one protein can be produced from a single gene as a result of alternative RNA
splicing

Question 3

The endoplasmic reticulum (ER)

Answer 3

forms a network of membrane tubules continuous with the
nuclear membrane

Question 4

The Golgi apparatus

Answer 4

is a series of flattened membrane discs

Question 5

Lysosomes

Answer 5

are membrane-bound organelles containing a variety of hydrolases that digest
proteins, lipids, nucleic acids and carbohydrates

Question 6

Vesicles

Answer 6

transport materials between membrane compartments

Question 7

Lipids and proteins are synthesised in…

Answer 7

the ER

Question 8

The synthesis of all proteins begins in…

Answer 8

cytosolic ribosomes

Question 9

signal sequence

Answer 9

Transmembrane proteins carry these which halt translation and directs the ribosome synthesising the protein to dock with the ER to form RER

Question 10

Once the proteins are in the ER, they are transported by…

Answer 10

vesicles that bud off from the ER
and fuse with the Golgi apparatus

Question 11

post-translational modification

Answer 11

occurs in the Golgi apparatus as proteins move through it. This is the addition of carbohydrates to the protein.

Question 12

Vesicles that leave the Golgi apparatus take proteins to…

Answer 12

the plasma membrane and
lysosomes

Question 13

Vesicles move along…

Answer 13

microtubules to other membranes and fuse with them within the cell

Question 14

Secreted proteins are translated in

Answer 14

ribosomes on the RER and enter its lumen. The proteins move through the Golgi apparatus and are then packaged into secretory
vesicles

Question 15

How are secretory proteins released from the cell?

Answer 15

vesicles move to and fuse with the plasma membrane, releasing the proteins out of
the cell

Question 16

How are inactivated secretory proteins activated?

Answer 16

proteolytic cleavage

Question 17

Primary structure

Answer 17

the sequence in which the amino acids are synthesised into the polypeptide

Question 18

How are secondary structures formed and what are they?

Answer 18

Hydrogen bonding along the backbone of the protein strand results in regions of secondary
structure — alpha helices, parallel or anti-parallel beta-pleated sheets, or turns

Question 19

tertiary structure

Answer 19

The polypeptide folds into a conformation that is stabilised by interactions between R groups: hydrophobic interactions;
ionic bonds; London dispersion forces; hydrogen bonds; disulfide bridges

Question 20

Quaternary structure

Answer 20

exists in proteins with two or more connected polypeptide subunits

Question 21

prosthetic group

Answer 21

a non-protein unit tightly bound to a protein and necessary for its function

Question 22

ligand

Answer 22

a substance that can bind to a protein. R groups not involved in protein folding can allow binding to ligands.

Question 23

When a ligand binds to a protein…

Answer 23

The conformation of the protein changes and therefore its function changes.

Question 24

Allosteric interactions occur between..

Answer 24

spatially distinct sites

Question 25

allosteric proteins consist of

Answer 25

multiple sub-units (quaternary structure)

Question 26

co-operativity

Answer 26

changes in binding at one subunit alter the affinity of the remaining subunits

Question 27

Modulators

Answer 27

Modulators regulate the activity of the enzyme when they bind to the allosteric site. Following binding of a modulator, the conformation of the enzyme changes and this alters the affinity of the active site for the substrate

Question 28

co-operativity in haemoglobin

Answer 28

When oxygen binds at one sub-unit of haemoglobin this changes the conformation of the remaining sub-units, increasing their affinity.

Question 29

A decrease in pH and an increase in temperature...

Answer 29

lowers the affinity of haemoglobin for oxygen. Therefore the binding of oxygen to haemoglobin is reduced.

Question 30

common form of post-translational modification

Answer 30

The addition or removal of phosphate can cause reversible conformational change in proteins

Question 31

Protein kinases

Answer 31

catalyse the transfer of a phosphate group to other proteins The terminal phosphate of ATP is transferred to specific R groups

Question 32

Protein phosphatases

Answer 32

catalyses the removal of a phosphate group from a protein

Question 33

Phosphorylation

Answer 33

brings about conformational changes, which can affect a protein’s activity The activity of many cellular proteins, such as enzymes and receptors, is regulated in this way Some proteins are activated by phosphorylation while others are inhibited