Genetics of living systems

Question 1

Mutation -

Answer 1

Changes in the sequence of the bases of DNA, the change in sequence is caused by substitution, deletion or insertion.

Question 2

Substitution in a nucleotide -

Answer 2

Changes in the codon which it occurs. This code may form a different amino acid resulting in a difference of the primary structure of a protein. Due to the genetic code being degenerate the new codon may still code for the same amino acid leading to no change in protein synthesis.

Question 3

Degenerate -

Answer 3

More codons than amino acids therefore amino acids can be coded by more than 1 codon.

Question 4

The insertion or deletion of a nucleotide leads to -

Answer 4

Frameshift mutation (the triplet code means that the sequence is transcribed consecutively in non-overlapping groups of three)

Question 5

Effects of different mutations may be -

Answer 5

No effects, damaging or beneficial

Question 6

No effect of mutation may cause no effect -

Answer 6

No effect on the phenotype because normally functioning proteins are still synthesised.

Question 7

How can mutations be damaging?

Answer 7

The phenotype of organism is affected negatively because the proteins are no synthesised or fully functional which can interfere with one or more essential processes.

Question 8

Explain how such rare mutations may be beneficial?

Answer 8

May result in a more useful characteristic in the phenotype, for example mutation in a protein present in the plasma membrane of human cells means HIV cannot bind and enter cells.

Question 9

Mutations can occur randomly in DNA replication but the rate of mutations can occur because of?

Answer 9

Mutagens

Question 10

What are mutagens?

Answer 10

Chemical, physical or biological reagent causing mutation.

Question 11

Genes can be regulated by a number of different factors (Protein synthesis) -

Answer 11

Transcriptional - turned on or off
Post transcriptional - mRNA can be modified which regulated translation and the proteins produced

Translation - stopped or started
Post-translation
Post-translational - Proteins can be modified after synthesis

Question 12

Operon -

Answer 12

A group of genes that are under control of the same regulatory mechanism and are expressed at the same time. Far more in common in prokaryotes than eukaryotes.

Question 13

Lac operon is a group of three genes -

Answer 13

Lac z, Lac y and Lac a

Question 14

What are the genes involved in the lac operon?

Answer 14

Involved in the metabolism of lactose which is a structural gene as they code for three enzymes.

Question 15

What 3 enzymes does the regulatory gene of lac operon code for?

Answer 15

Beta galactosidase, lactose permease and transacetylase. (transcribed onto a long single molecule of mRNA)

Question 16

Order of lac operon 1.

Answer 16

Regulatory gene - operator - promoter - structural gene x3 at this point a repressor protein is attached to the operator.

Question 17

The regulatory gene is located closest to and what does the thing its next to do?

Answer 17

The operator codes for the repressor proteins which.

Question 18

What does the repressor protein do on the operator -

Answer 18

Prevents transcription of the structural gene in the absence of lactose.

Question 19

The RNA polymerase cannot bind to the promotor due to -

Answer 19

Repressor protein. Called down regulation

Question 20

When lactose is present in the lac operon what happens -

Answer 20

It binds to the repressor protein causing it to change shape and cannot complementary fit on the operator, as a result there is space for the promotor region and allows RNA polymerase to bind to it transcribing the structural genes and the enzymes are synthesised.

Question 21

The process of transcription is relatively slow from the process of the RNA polymerase the required quantity of enzymes produces efficiently is also achieved by another protein binding -

Answer 21

cAMP.

Question 22

Post-transcriptional factors of RNA processing -

Answer 22

A cap is added to the 5’ end and a tail is added to the 3’ end. Which can be used to stabilise the mRNA and delay the degredation in the cytoplasm.

Question 23

RNA editing -

Answer 23

The nucleotide of some mRNA can also be changed through the base addition, deletion or submission, this can result in a different range of proteins that can be produced from a single mRNA strand.

Question 24

Translational control (processes which can be used to regulate processes of protein synthesis) -

Answer 24

Degradation of mRNA - more resistant the molecule the longer it will last in the cytoplasm

Question 25

Protein kinases -

Answer 25

Enzymes that catalyse the addition of phosphate groups to proteins and this changes the tertiary structure of the proteins and therefore the function of the protein.

Question 26

Homeobox genes -

Answer 26

Group of genes which contain a homeobox are regulatory genes which code for on and off genes. Specifying cell identity and positioning during embryonic development

Question 27

Hox genes -

Answer 27

Group of homeobox genes only present in animals, responsible for the correct positioning of body parts. Represented through a cross sections.

Question 28

Mitosis and apoptosis in the formation of body plans -

Answer 28

Mitosis:
- Increase number of cells leading to growth
Apoptosis:
- Can work by removing unwanted cells and tissues (like sculpting wood)
- Therefore, cell apoptosis can reduce chemical signals which stimulate mitosis and cell proliferation leading to remodelling of tissue.

Question 29

Factors affecting the expression of regulatory genes -

Answer 29

Can be from internal and external. Growth and development of an organism can result from factors such as stress and light.

Question 30

Drugs can affect regulatory genes expression -

Answer 30

Thalidomide, resulted in the formation of shortened limbs as it was given to pregnant women.