Control of Gene Expression 3.12-3.14

Question 1

Define ‘tissue’ + give example

Answer 1

A tissue is a group of similar cells that are specially adapted to work together to carry out a particular function
Eg. Xylem tissue contains xylem vessels cells and parenchyma cells

Question 2

Define ‘organ’

Answer 2

A group of different tissues that work together to perform a particular function

Question 3

Give an example of an organ in a plant and describe the various tissues

Answer 3

The leaf is an organ:

• lower epidermis
• spongy mesophyll
• palisade mesophyll
• upper epidermis
• phloem/xylem

Question 4

Define ‘organ system’ + example

Answer 4

A group of organs working together to perform a particular function
Eg. Respiratory system

Question 5

Give an example of an organ in an animal and describe the various tissues

Answer 5

Lungs:

• Squamous epithelium tissue
• Fibrous connective tissue
• Endothelium tissue

Question 6

What is a genome?

Answer 6

The entire set of DNA in a cell, including all the genes

Question 7

How do stem cells become specialised?

Answer 7

Through differential gene expression

Question 8

Do stem cells all contain the same genes?

Answer 8

Yes

Question 9

Why are not all of the genes expressed in stem cells?

Answer 9

Not all of them are active

Question 10

Explain differential gene expression:

Answer 10

• mRNA is transcribed from active genes
• mRNA from active genes is then translated into proteins
• proteins modify the cell determine the cell structure and controlling cell processes
• changes cause the cell to become specialised - difficult to reverse

Question 11

What can gene expression be controlled by?

Answer 11

Transcription factors which alters the rate of transcription of genes
Eg. Increased transcription produces more mRNA used to make more protein

Question 12

What are transcription factors?

Answer 12

Proteins that bind to DNA and activate or deactivate genes by increasing or decreasing the rate of transcription

Question 13

What are factors that increase the rate of transcription called? How do they work?

Answer 13

Activators - work by helping RNA polymerase bind to DNA to begin transcription

Question 14

What are factors that decrease the rate of transcription called? How do they work?

Answer 14

Repressors - prevent RNA polymerase binding to DNA so stop transcription

Question 15

Where do transcription factors bind to in eukaryotes?

Answer 15

Specific DNA sites near the start of target genes

Question 16

Where do transcription factors bind to in prokaryotes?

Answer 16

Operons

Question 17

What is an operon?

Answer 17

A section of DNA that contains a cluster of structural genes, that are transcribed together, as well as control elements and sometimes a regulatory gene

Question 18

What does E. Coli respire normally? What does it respire when this isn’t available?

Answer 18

Glucose when available

Lactose otherwise

Question 19

Where are the genes found that produce the enzymes needed to respire lactose in E. Coli?

Answer 19

On the lac operon

Question 20

What are the three structural genes of lac operon?

Answer 20

LacZ, LacY and LacA (help bacteria digest lactose)

Question 21

What do structural genes code for?

Answer 21

Useful proteins

Question 22

What are control elements made from?

Answer 22

Promoter = DNA sequence located before structural genes that RNA polymerase binds to 
Operator = DNA sequence that transcription factors bind to

Question 23

What does a regulatory gene code for?

Answer 23

An activator or a repressor

Question 24

Describe what happens when lactose is NOT a present?

Answer 24

Regulatory gene produces the lac repressor which is a transcription factor that binds to the operator site, blocking transcription because RNA polymerase can’t bind

Question 25

Describe what happens when lactose is present?

Answer 25

Lactose binds to the repressor, changing the repressors shape so it can no longer bind to operator site.
RNA polymerase can now begin transcription of structural genes

Question 26

What is an organisms phenotype the result of?

Answer 26

The genotype interacting with the environment

Eg. If a child is malnourished they may not reach their full height

Question 27

What does epigenetic control determine.

Answer 27

In eukaryotes, epigenetic control determines whether certain genes are expressed, altering the phenotype

Question 28

How does epigenetic control work?

Answer 28

It does NOT alter the base sequence of DNA but instead works by attaching or removing chemical groups to or from DNA which alters how easy it is for next the transcription of genes

Question 29

Describe two methods of epigenetic control

Answer 29

Methylation and acetylation

Question 30

Describe methylation

Answer 30

• A methyl group attaches to DNA at a CpG site (cytosine and guanine base next to each other)
• Changes the DNA structure so that proteins/enzymes needed for transcription can’t bind to gene
• Gene is repressed

Question 31

What are histones?

Answer 31

Proteins that DNA wrap around to form chromatin (which makes up chromosomes) which can be either highly condensed or less condensed

Question 32

Describe acetylation

Answer 32

• Histones are acetylated making the chromatin less condensed which means that proteins involved in transcription can bind to DNA allowing genes to be transcribed
  (Opposite for removal of acetyl groups)

Question 33

How can epigenetic changes be passed on after cell division?

Answer 33

When a cell divides and replicated, epigenetic changes can be passed on to daughter cells which means that certain genes that are activated/deactivated in original cells will also be activated/deactivated in daughter cells