1.2a the proteome + the synthesis and transport of proteins

Question 1

What is the proteome?

Answer 1

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

Question 2

Why is the proteome larger than the number of genes?

Answer 2

• particularly in eukaryotes

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

Question 3

What are genes that do not code for proteins called?

Answer 3

non-coding RNA genes

Question 4

What are 3 example of non-coding RNA genes?

Answer 4

• those that are transcribed to produce tRNA and RNA

- RNA molecules that control the expression of other genes

Question 5

Not all…

Answer 5

…genes are expressed as proteins in a particular cell type

Question 6

What can happen to the set of proteins expressed by a give cell type?

Answer 6

it can vary over time and under certain conditions

Question 7

Give 4 examples of some factors affecting the set of proteins expressed by a given cell type

Answer 7

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

Question 8

Why do eukaryotes have a system of internal membranes?

Answer 8

• increases the total area of membrane
• because of their size eukaryotes have a relatively small surface area to volume ratio
• the plasma membrane of eukaryotic cells is therefore too small to carry out all the vital functions carried out by membranes

Question 9

Give a description of the endoplasmic reticulum

Answer 9

forms a network of membrane tubules continuous with the nuclear membrane

Question 10

Give a description of the Golgi apparatus

Answer 10

a series of flattened membrane discs

Question 11

Give a description of lysosomes

Answer 11

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

Question 12

Give a description of vesicles

Answer 12

transport material between membrane compartments

Question 13

Where are lipids and proteins synthesised?

Answer 13

the ER

Question 14

Give a description of the RER (Rough ER)

Answer 14

RER has ribosomes on its cytosolic face

Question 15

Give a description of the SER (Smooth ER)

Answer 15

lacks ribosomes

Question 16

Describe the synthesis of lipids

Answer 16

lipids are synthesised in the SER and inserted into its membrane

Question 17

Where does the synthesis of all proteins begin?

Answer 17

cytosolic ribosomes

Question 18

Describe the sysnthesis of cytosolic proteins

Answer 18

• the synthesis of all proteins begins in cytosolic ribosomes
• the synthesis if cytosolic ribosomes is completed there, and these proteins remain in the cytosol

Question 19

describe the sysnthesis of transmembrane proteins

Answer 19

• the sysnthesis of all preoteins begins in cytosolic ribosomes
• transmembrane proteins carry a signal sequence, which halts translation and directs the ribosome synthesising the protein to dock with the ER
• forming RER
• translation continues after docking, and the protein is inserted into the membrane of the ER

Question 20

What is a signal sequence?

Answer 20

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

Question 21

What happens to proteins once they are in the ER?

Answer 21

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

Question 22

Describe what happens to proteins as the move through the Golgi apparatus

Answer 22

• they undergo post-translational modification
• molecules move through the Golgi discs in vesciles 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 carbohydrates

Question 23

What is the major modification to proteins in the Golgi?

Answer 23

the addition of carbohydrates

Question 24

What happens to vesicles that leave the Golgi apparatus?

Answer 24

-they take proteins to the plasma membrane and lysosomes

Question 25

How do vesicles move through the cell?

Answer 25

vesicles more along microtubules to other membranes and fuse with them within the cell

Question 26

What happens to secreted proteins?

Answer 26

• they are translated on ribosomes on the RER and enter its lumen
• 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

Question 27

what is the lumen?

Answer 27

the inside space of a tubular structure

Question 28

What happens to many secreted proteins?

Answer 28

Many secreted proteins are synthesised as inactive precursors and require proteolytic cleavage to produce active proteins

Question 29

What is proteolytic cleavage?

Answer 29

Another type of post translational modification

Question 30

Give an example of secreted proteins that require proteolytic cleavage to become active

Answer 30

-Digestive enzymes

Question 31

Give 2 examples of secreted proteins

Answer 31

• Peptide hormones

- digestive enzymes