6.1.1 Cellular Control

Question 1

Genes can be switched on and off

Answer 1

Not all genes are expressed to make a functional protein in all cells.
Can be controlled at transcriptional, post transcriptional, post translational levels.

Question 2

Transcriptional level control - Transcription factors

Answer 2

Transcriptional control.
Transcription factors are proteins that bind to DNA and switch genes on or off by controlling transcriptional rate. Activators - increase. Repressions - decrease.
The shape of a transcription factor determines whether it can bind to DNA and can be altered by molecules binding e.g. hormones and sugars.

Question 3

Operon

Answer 3

• Structural genes - code for functional proteins
• Control elements - promoter and operator
• Regulatory gene - codes for activator or repressor

Question 4

Lac Operon

Answer 4

E. coli respires using glucose, when glucose isn’t present it can use hydrolysed lactose.
3 structural genes:
- lacZ
- lacY
- lacA

These produce 2 proteins:
- Beta galactosidase (hydrolyse lactose)
- Lactose permease (active transport of lactose)

Question 5

When lactose isn’t present

Answer 5

• Regulatory gene (lacI) produces a lac repressor protein
• Repressor binds to operator
• Blocks transcription as RNA polymerase can’t attach to promoter
• Conserves energy

Question 6

When lactose is present

Answer 6

• Lactose binds to lac repressor
• Lac repressors shape changes and it can no longer bind to operator
• RNA polymerase can begin transcription

Question 7

Post transcriptional level - Splicing

Answer 7

In eukaryotic DNA some regions don’t code for amino acids. The coding regions are exons, the non coding are introns. During transcription they are both copied into preMRNA. Introns are removed by splicing and exons are joined.

Question 8

Post translational level - cAMP

Answer 8

Some proteins aren’t functional straight after synthesis, they need to be activated. This is controlled by molecules e.g. hormones and sugars. Some of theses molecules bind to cell membranes and trigger cAMP production. cAMP activates proteins in cells by altering 3D structure e.g. making the active site more or less active.

Question 9

Body plan

Answer 9

General structure of an organism. Body parts arranged in a particular way.

Question 10

Homeobox genes

Answer 10

Control anatomical development/body plan. Regulatory genes. 180 bases. Code for homeodomain - 60 amino acid chain. Highly conserved - maintained by natural selection and unchanged.

Question 11

Hox genes

Answer 11

Only in animals. Develop where and what limbs.

Question 12

Mitosis and differentiation

Answer 12

Creates the bulk of the body.

Question 13

Apoptosis

Answer 13

Removes the unwanted bits.

• Cell shrinks
• Blebbing of membrane
• Nucleus disintegrates
• Phagocytic receptors recognise surface phospholipids
• Engulfed

Question 14

Internal stimuli

Answer 14

• DNA damage
• Stress
• Hormones

Question 15

Mutations

Answer 15

Change to base sequence of DNA.

Question 16

Subsitution

Answer 16

One or more bases are swapped for another.

Question 17

Deletion

Answer 17

One or more bases are removed.

Question 18

Insertion

Answer 18

One or more bases are added.

Question 19

Frameshift

Answer 19

Causes different position of bases e.g. moved down or up. Insertion or deletion may cause this.

Question 20

Neutral

Answer 20

Change in a base but may still code for the same amino acid (degenerate).
May code for different amino acid but that amino acid may be chemically similar so no effect on protein.
May code for an unrelated function so the protein works normally.

Question 21

Beneficial

Answer 21

Advantageous effect on an organism, increasing chance of survival.

Question 22

Harmful

Answer 22

Disadvantageous effect on an organism, decreasing chance of survival.