Cellular Control

Question 1

What are the functions of transcription factors in eukaryotic cells?

Answer 1

• regulation of gene expression by activating/inhibiting binding of RNA polymerase
• only certain genes in specific cell types expressed - role in cell differentiation
• regulate cell cycle and division

Question 2

How can chromosome translocation cause abnormalities in a cell?

Answer 2

Chromosome may have broken at promoter region - gene separated. Not on/off anymore, stops cell dividing abnormally - rapid cell division —> cancer. New DNA sequence.

Question 3

Name 3 types of point mutation.

Answer 3

Silent, aa code = degenerate and codes for same aa so not affect primary structure
Missense, triplet codes for different aa - primary and tertiary changed so no longer function
Nonsense, triplet codes for stop codon and protein truncated and be degraded

Question 4

Explain why an index mutation has a bigger effect on a protein than a point mutation.

Answer 4

Indel mutations often result in a frame shift. Because of the triplet, non-overlapping genetic code - all aa coded for downstream of the mutation may be different so the primary and tertiary structures of the protein
will be very different.
Point mutations only change max of 1aa in the sequence -
limited impact on primary and tertiary structures.

Question 5

Name 3 levels of regulating gene expression.

Answer 5

Transcriptional,
Post transcriptional,
Post translational,

Question 6

Explain how the presence of lactose induces the expression of enzymes that can metabolise lactose.

Answer 6

Lactose binds to the repressor protein—> change shape and preventing it from binding to the operator. This means RNA polymerase can now bind to the promoter region and transcribe the genes encoding the enzymes.

Question 7

How do transcriptional factors turn on a gene?

Answer 7

Bind to promoter region and help RNA polymerase to bind so increasing transcription of gene.

Question 8

Explain difference between introns and exons and describe how allow for post transcriptional regulation.

Answer 8

Introns are non coding DNA regions but exons are coding. Alternative splicing allows production of different mRNA sequences from 1 DNA section.

Question 9

How are many proteins activated?

Answer 9

Phosphorylation.

Question 10

What is a promoter region?

Answer 10

Binding site for RNA polymerase so transcription can happen.

Question 11

What is a transcription factor?

Answer 11

Protein, can combine with specific site on DNA.

Question 12

What is a repressor protein?

Answer 12

Inhibits expression of one or more genes.

Question 13

What is splicing?

Answer 13

The process where pre mRNA becomes mRNA by removing introns and attaching exons.

Question 14

What is an operon and why is it useful?

Answer 14

Group of genes which act as single transcriptional unit. Useful because genes coding for proteins in specific metabolic path can all be turned on/off.

Question 15

Name the 2 types of indel mutations.

Answer 15

Indel - not in 3s, leads to frame shift because non overlapping code. Nonfunctional protein
Expanding triplet repeats - add aa to primary structure

Question 16

How does a lac operon work?

Answer 16

Gene lacZ codes for beta galactosidase enzyme - hydrolyses lactose to form glucose and galactose.
Gene lacY codes for membrane carrier protein lactose permeate - can enter bacterial cell.
Regulatory gene lacI codes for protein - prevents transcription of structural genes = repressor protein.
Promoter region = where RNA polymerase binds to start transcription.
Operator region = DNA section repressor protein binds to and stops transcription.

Question 17

Why is the lac operon important?

Answer 17

Glucose is not always available as the main respiratory substrate. To conserve energy, lactose metabolic proteins only made when no glucose present. Expression of all proteins easily repressed when not needed.

Question 18

Why are transcription factors needed?

Answer 18

Regulatory gene lacI always on to form repressor protein. Binds to operator region and stops RNA polymerase binding.
Lactose acts as inducer because binds to repressor protein which changes shape.

Some factors are activators, some are repressors.

Question 19

What are examples of transcription factors?

Answer 19

• RNA polymerase and factor cluster forms a complex known as a transcription initiation complex
• acts within nucleus - genes on/off because slide along part of DNA and binds to specific promoter regions. Activate/suppress gene transcription.
• specific factors affect action of RNA polymerase
• regulate cell cycle

Question 20

How is gene expression regulated on the post transcriptional level?

Answer 20

Introns and exons are both transcribed to form primary mRNA which forms mature mRNA = genetic material translated into a protein.
- edited and introns removed
- remaining exons are joined = SPLICING
Catalysed by splicosome
Endocnuclease may be used in editing and splicing - bases in RNA indel/substituted.

A 5’ cap is added and a polyA tail.

Question 21

How does alternative splicing work?

Answer 21

Some introns may encode proteins.
Some are short, non coding RNA lengths in gene regulation.

Splicing can also remove some exons so different combinations of mature mRNA - 1 gene can form different mRNAs and code for many proteins.

Question 22

What are the steps of gene regulation at the post translational level?

Answer 22

1. Signalling molecule binds to receptor on membrane
2. Conformational change in G protein - activates
3. G protein activates ardently cyclase enzymes
4. Catalyses form many cAMP from ATP
5. CAMP activated PKA (protein kinase A)
6. PKA causes the phosphorylation of enzymes via ATP hydrolysis - activates many cytoplasmic proteins
7. PKA phosphorylates CREB (cAMP response element binding)
8. Enters nucleus and acts as a transcription factor

Question 23

What are the similarities between homeobox and Hox genes?

Answer 23

• regulate body plan
• have 180 base pairs = homeobox sequence
• encode proteins = transcription factors
• highly conserved sequence
• 60 aa long - homeodomain

Question 24

What are the differences between homeobox and Hox genes?

Answer 24

Hox is more specific - only in animals, specifically control a-p
Homeobox have more functions

Question 25

What is the function of homeobox genes?

Answer 25

Regulate pattern of anatomical development and ensure all structures develop in the correct location.
180 base pairs that are highly conserved in plants, animals, fungi.
Essential for regulation and development of differentiation.

60 aa = homeodomain sequence can bind to DNA and act as a transcription factor.

Question 26

What is the function of Hox genes?

Answer 26

Sub group of homeobox. Only in animals and encode homeodomain proteins.
Development of embryos anterior-posterior axis. Active in early development.
Found in clusters - when mutate, body parts develop in the wrong place.

When it is expressed, encodes specific homeodomain which acts as a transcription factor. Regulate mitosis, cell differentiation and apoptosis.

Question 27

What is spatial co-linearity?

Answer 27

The order of the genes corresponds to where they are expressed along the a-p axis.

Question 28

What is apoptosis?

Answer 28

Programmed cell death for removal of old/damaged/unwanted cells.

Question 29

What is the process of apoptosis?

Answer 29

1. Enzymes digest the cytoskeleton so the cell shrinks
2. Cytoplasm becomes dense and tightly packed with organelles
3. Cells membrane forms bless
4. Chromatin condenses and the nuclear envelope breaks down + cell fragments
5. Cell breaks into vesicles which are engulfed by phagocytosis

Question 30

Why is apoptosis so important for development?

Answer 30

Used to prevent extensive cell division and to shape different body parts.
- removes harmful immune cells that may attack the body
- signalling molecules can trigger it, which are produced in response to internal/external stimuli eg. Cellular stress, transcription factor