Unit 1 - Cells and Protein - 1.2 Protein

Question 1

a) The proteome

Answer 1

a+

Question 2

What is the proteome?

Answer 2

The proteome is the entire set of proteins expressed by a genome.

Question 3

What is the genome?

Answer 3

The genome is the entire heriditary information of an organism encoded in DNA.

Question 4

What about the size of the proteome of eukaryotes?

and why?

Answer 4

The proteome is larger than the number of genes, particularly in eukaryotes

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

Question 5

What are not all genes?

Answer 5

expressed as proteins in a
particular cell type

Question 6

What are genes that do not code for proteins called?

and what do these genes include?

Answer 6

non-coding RNA genes

those that are transcribed to produce tRNA, rRNA, and RNA molecules that control the expression of other genes.

Question 7

What are some factors affecting the set of proteins expressed by a given cell type?

Answer 7

the metabolic activity of the cell cellular stress
the response to signalling molecules
diseased versus healthy cells

Question 8

b) The synthesis and transport of proteins

i) Intracellular membranes

Answer 8

a+

Question 9

What do eukaryote cells have?

Answer 9

a system of internal membranes, which increases the total area of
membrane

Question 10

What is as a result of the size of eukaryote?

What does this result in?

Answer 10

eukaryotes have a
relatively small surface area to volume ratio.

The plasma membrane of eukaryotic cells is therefore too small an area to carry out all the vital functions carried out by membranes.

Question 11

What is the Endoplasmic Reticulum?

Answer 11

forms a network of membrane tubules continuous with the nuclear membrane.

Question 12

What is the Golgi Apparatus?

Answer 12

a series of flattened membrane discs

Question 13

What are Lysosomes?

Answer 13

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

Question 14

What are vesicles?

Answer 14

transport materials between
membrane compartments

Question 15

b) The synthesis and transport of proteins

ii) Synthesis of membrane components

Answer 15

a+

Question 16

What are synthesised in the ER?

Answer 16

Lipids and Proteins

Question 17

What is the difference between the Rough ER and the Smooth ER?

Answer 17

Rough ER (RER) has ribosomes on its
cytosolic face while smooth ER (SER) lacks ribosomes.

Question 18

What happens in the synthesis of lipids?

Answer 18

Lipids are synthesised in the smooth
endoplasmic reticulum (SER) and inserted into its membrane

Question 19

What happens in the synthesis of proteins?

Answer 19

The synthesis of all proteins begins in
cytosolic ribosomes.

The synthesis of cytosolic proteins is
completed there, and these proteins remain in the cytosol.

Question 20

What do transmembrane proteins do?

Answer 20

carry a signal sequence, which halts translation and directs the ribosome synthesising the protein to dock with the ER, forming RER.

Question 21

What is a signal sequence?

Answer 21

a short stretch of amino acids at one end of the polypeptide that determines the eventual location of a protein in a cell.

Question 22

When then happens after docking?

Answer 22

Translation continues, and the
protein is inserted into the membrane of the ER.

Question 23

b) The synthesis and transport of proteins

iii) Movement of proteins between
membranes

Answer 23

a+

Question 24

What happens once proteins are in the ER?

Answer 24

they are transported by vesicles that bud off from the ER and fuse with the Golgi apparatus.

Question 25

What then happens?

Answer 25

as proteins move through the Golgi apparatus they undergo post translational modification.

Question 26

What then happens?

Answer 26

Molecules move through the Golgi discs in vesicles that bud off from one disc and fuse to the next one in the stack. Enzymes catalyse the addition of various sugars in multiple steps to form the carbohydrates.

Question 27

What is the major modification?

Answer 27

The addition of carbohydrate groups.

Question 27

What then happens to vesicles that leave the Golgi Apparatus?

Answer 27

The vesicles take proteins to the plasma membrane and lysosomes. Vesicles move along microtubules to other membranes and fuse with them within the cell

Question 28

b) The synthesis and transport of proteins iv) The secretory pathway

Answer 28

a+

Question 29

How are secreted proteins produced?

Answer 29

translated in ribosomes on the RER and enter its lumen.

Question 30

What are examples of secreted proteins?

Answer 30

Peptide hormones Digestive enzymes

Question 31

What are the stages of the secretory pathway?

Answer 31

The proteins move through the Golgi apparatus and are then packaged into secretory vesicles. These vesicles move to and fuse with the plasma membrane, releasing the proteins out of the cell. Many secreted proteins are synthesised as inactive precursors and require proteolytic cleavage to produce active proteins.

Question 32

What is proteolytic cleavage?

Answer 32

Proteolytic cleavage is another type of posttranslational modification.

Question 33

What is an example of a secreted protein that require proteolytic cleavage to become active?

Answer 33

Digestive Enzymes.