(6.1.1) Cellular Control

Question 1

Define Mutation

Answer 1

change in the sequence of bases in DNA

Question 2

The change in base sequence can be caused by:

Answer 2

• Substitution
• Deletion
• Insertion

Question 3

What can the insertion or deletion of a nucleotide lead to?

Answer 3

A frameshift mutation

Question 4

What are the 3 effects of different mutations?

Answer 4

• No effect
• Damaging - phenotype
  affected in a negative way
• Beneficial - protein synthesised that results in a new and useful characteristics in the phenotype

Question 5

How is the rate of mutation increased?

Answer 5

Increased by mutagens

Question 6

What is a mutagen?

Answer 6

A chemical, physical, or biological agent which causes mutations

Question 7

Example of physical mutations

Answer 7

• ionising radiation such as XRAYS - break one or both DNA strands - some breaks can be repaired but mutations can occur in the process

Question 8

Example of chemical mutations

Answer 8

deaminating agents - chemically alter bases in DNA such as converting cytosine to uracil in DNA changing the base sequence

Question 9

Examples of Biological agents

Answer 9

• Alkylating agents - methyl or ethyl groups are attached to bases resulting in the incorrect pairing of bases during replication
• Base analogs - incorporated into DNA in place of the usual during replication, changing the base sequence
  -Viruses - viral DNA may insert itself into a genome, changing the base sequence

Question 10

Explain how it is possible for a mutation to have no effect on the protein produced from that gene?

Answer 10

• some triplets code for the same amino acid bc they are degenerate
• so the amino acid sequence is not altered
• some alternative amino acids will not alter the shape of the protein

-the mutation occurs in intron so is removed

Question 11

Explain how a mutation could alter the protein so that it no longer performs its correct function in the cell?

Answer 11

• an insertion/deletion will cause a frame shift
• all triplets downstream will be different
• the protein will have a different sequence of amino acids after the mutation
• Therefore the tertiary structure will be different

Question 12

Mitosis is involved in growth and repair of tissues.
State two other roles of mitosis in multicellular organisms.

Answer 12

• development of body plan
• production of new stem cells
• asexual reproduction

Question 13

How is transcription controlled in eukaryotes?

Answer 13

• Hormone enters cell and binds to a transcription factor
• The transcription factor is activated
• This binds to the promoter region
• RNA polymerase is then able to bind

Question 14

Describe how gene expression can be regulated after transcription.

Answer 14

• The primary mRNA can be modified
• Removal of introns produces mature mRNA
• Alternative splicing can produce different versions of mRNA
• Protein has to be activated by cAMP/phosphorylation and the binding of cAMP alters the shape of the protein

Question 15

How does the structure of galactose allows it to be used as a respiratory substrate

Answer 15

The bonds contain energy so they can be broken by respiratory enzymes

They are also soluble so can move within the cell

The H/OH groups are able to form H bonds with water

Question 16

Suggest and explain why lactose cannot cross cell membranes

Answer 16

• Lactose is too big
• This means that it is unable to pass between phospholipids

-It may also have a small/no concentration gradient so requires a carrier protein to pass membranes.

Question 17

In order for lactose to enter the cytoplasm of E. coli a protein is required.

The E. coli living in the digestive system of young mammals are more likely to contain this protein than
E. coli living in the digestive system of old mammals.

Suggest an explanation for this observation.

Answer 17

Young mammals have a diet which is higher in milk. This means that it has a high lactose concentration.

The structural gene for the lactose permease gene / lacY is transcribed and switched on

The protein is lactose permease

Question 18

Why are fruit flies chosen for research into genes controlling the development of body plan?

Answer 18

• Low cost

-Rapid reproduction rate so more generations in a given time

-Fruit fly genetics is well understood

-Simple genetics/body plan

-Many mutations/structures are observable with light microscope

Question 19

The development of body plan in eukaryotic organisms is controlled by
……………………………………………… genes. These genes code for proteins that are able to bind
to ……………………………………………… and turn specific genes on and off and are known as
……………………………………………… factors. These proteins contain a sequence of base pairs
that varies little between species within the animal, ……………………………………………… or
fungus ……………………………………………… .

Answer 19

1) homeobox
2) DNA
3) Transcription
4) Plant
5) Kingdoms

Question 20

Investigations into the activity of genes that control body plan frequently use fruit flies and mice.

There are some public concerns about the ethics of using mice in these investigations.

Suggest two reasons why mice are chosen as a suitable species for investigation

Answer 20

They are more similar to humans

They are low cost

They have rapid reproduction rate

They show effects are generalisable to more than one species