6.1.1

Question 1

What is a mutation?

Answer 1

A mutation is a change in the DNA base sequence

Question 2

What are the three types of mutation?

Answer 2

Nucleotide substitution, deletion, or insertion

Question 3

What is a point mutation?

Answer 3

A mutation where only one nucleotide is affected

Question 4

What is a frameshift mutation and what causes it?

Answer 4

A mutation when the entire DNA base sequence is disrupted and moved up or down one. It is caused by base insertion or base deletion.

Question 5

When will the addition or deletion of nucleotides not cause a frameshift mutation?

Answer 5

When the number of nucleotides added or deleted is a multiple of three

Question 6

What are the three potential impacts of a mutation?

Answer 6

No effect - no impact on the phenotype at all
Damaging - the phenotype of an organism is impacted negatively because proteins are no longer synthesised or the proteins synthesised are non-functional
Beneficial - the phenotype of an organism is impacted positively due to a useful characteristic

Question 7

What is a mutagen?

Answer 7

A factor that increases the rate of mutation

Question 8

What are the three types of mutagens?

Answer 8

Chemical mutagens, physical mutagens, and biological agents

Question 9

Give an example of a physical mutagen.

Answer 9

Ionising radiations such as X-rays. They can break one or both DNA strands

Question 10

Give an example of a chemical mutagen.

Answer 10

Deaminating agents. They chemically alter bases in DNA such as converting cytosine into uracil, which changes the DNA base sequence

Question 11

Give three examples of biological agents.

Answer 11

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 base during replication, changing the DNA base sequence
Viruses - viral DNA may insert itself into a genome, changing the base sequence

Question 12

Give an example of a beneficial mutation.

Answer 12

The ability of humans to digest lactose

Question 13

How can chromosomes mutate?

Answer 13

Deletion - a section of chromosome breaks off and is lost within the cell
Duplication - sections get duplicated on a chromosome
Translocation - a section of a chromosome breaks off and joins another non-homologous chromosome
Inversion - a section of chromosome breaks off, is reversed, and then joins back onto the chromosome.

Question 14

What are the four ways in which genes are regulated?

Answer 14

Transcriptional control - genes can be turned on or off
Post-transcriptional control - mRNA can be modified which regulates translation and the types of proteins produced
Translational control - translation can be stopped or started
Post-translational control - proteins can be modified after synthesis which changes their functions

Question 15

What is chromatin remodelling?

Answer 15

Heterochromatin is tightly wound DNA causing chromosomes to be visible during cell division, while euchromatin is loosely wound DNA present during interphase. Transcription of genes is not possible when DNA is tightly packed because RNA polymerase cannot access the genes. Therefore, protein synthesis only takes place during interphase.

Question 16

How is chromatin remodelling helpful?

Answer 16

It ensures the proteins necessary for cell division are synthesised in time, and prevents protein synthesis from taking place during cell division as it requires lots of energy.

Question 17

What is histone modification?

Answer 17

DNA coils around histones as they are positively charged and DNA is negatively charged, but they can be altered to increase or decrease the degree of packing.

Question 18

What are the three types of histone modification?

Answer 18

Acetylation, phosphorylation, and methylation

Question 19

Describe acetylation and phosphorylation.

Answer 19

Acetylation and phosphorylation are when acetyl groups and phosphate groups respectively are added, which reduces the positive charge of the histones. This causes DNA to coil less tightly, allowing certain genes to be transcribed.

Question 20

Describe methylation.

Answer 20

The addition of methyl groups which makes the histones more hydrophobic causing them to bind more tightly to each other, meaning DNA coils more. This prevents the transcription of genes

Question 21

What is an operon?

Answer 21

An operon is a group of genes that are under the control of the same regulatory mechanism and are expressed at the same time. They are an efficient way of saving resources because if a certain gene products are not needed, then all of the genes involved in their production can be switched off.

Question 22

Why are operons more common in prokaryotes than eukaryotes?

Answer 22

Prokaryotes have a smaller and simpler structure of their genomes.

Question 23

Describe how the lac operon works.

Answer 23

If glucose is in short supply, lactose can be used as a respiratory substrate. Different enzymes are required to metabolise lactose. The lac operon is a group of three genes, lacZ, lacY, and lacA, involved in the metabolism of lactose. They are structural genes as they code for three enzymes and are transcribed onto a single long molecule of mRNA. A respiratory gene, lacI, is located near to the operon and codes for a repressor protein that prevents the transcription of the structural gene in the absence of lactose.

Question 24

What are the operator and promoter?

Answer 24

The operator is an area close to the structural genes, and is bound to the repressor protein. The binding of the protein prevents RNA polymerase binding to DNA and beginning transcription. This is called down regulation.

The promoter is the section of DNA that is the binding site for RNA polymerase.

Question 25

What happens when lactose is present?

Answer 25

Lactose binds to the repressor protein, causing it to change in shape, and so it can no longer bind to the operator. Therefore, RNA polymerase can bind to the promoter, and the enzymes are synthesised.

Question 26

What is the role of cyclic AMP?

Answer 26

The binding of RNA polymerase only results in a slow rate of transcription that needs to be increased or up-regulated to produce the required quantity of enzymes to metabolise lactose efficiently. This is achieved by the binding of CRP, which is only possible when CRP is bound to cAMP. The transport of glucose into an E.coli cell decreases the cAMP levels, reducing the transcription of genes for metabolism of lactose
.

Question 27

Give examples of post-transcriptional control.

Answer 27

RNA processing and RNA editing

Question 28

Describe RNA processing.

Answer 28

The product of transcription is pre-mRNA. This is modified forming mature mRNA before it can bind to a ribosome and code for the synthesis of the required protein. A cap, which is a modified nucleotide, is added to the 5’ end and a tail, a long chain of adenine nucleotides, is added to the 3’ end. These both stabilise mRNA and delay degradation in the cytoplasm. The cap also aids binding of mRNA to ribosomes.
Splicing also takes place, where RNA is cut at specific places. The introns are removed and the exons are joined together.

Question 29

Describe RNA editing.

Answer 29

The nucleotide sequence of some mRNA molecules can also be changed via base addition, deletion, or substitution. These have the same effect as point mutations and result in the synthesis of different proteins which may have different functions. This increases the range of proteins that can be produced from a single mRNA molecule or gene.

Question 30

How is protein synthesis regulated?

Answer 30

Degradation of mRNA means that the more resistant the molecule, the longer it will last in the cytoplasm, so a greater quantity of protein is synthesised.
Binding of inhibitory proteins to mRNA prevents it binding to ribosomes and the synthesis of proteins.
Activation of initiation factors which aid the binding of mRNA to ribosomes.

Question 31

What are protein kinases?

Answer 31

Protein kinases are enzymes that catalyse the addition of phosphate groups to proteins. The addition of a phosphate group changes the tertiary structure and so the function of a protein. Many enzymes are activated by phosphorylation. Protein kinases are therefore important regulators of cell activity. Protein kinases are themselves often activated by cAMP.

Question 32

Describe some measures of post-translational control.

Answer 32

Post-translational control involves the modification of proteins that have been synthesised. For example, non-protein groups may be added, amino acids may be modified, proteins are shortened or folded, and are modified by cAMP.

Question 33

What is morphogenesis?

Answer 33

The regulation of the pattern of anatomical development

Question 34

What are homeobox genes?

Answer 34

Homeobox genes are a group of genes that all contain a homeobox.

Question 35

What is a homeobox?

Answer 35

A homeobox is a section of DNA that is 180 base pairs long. A homeobox codes for a part of the protein 60 amino acids long that is highly conserved in plants, animals, and fungi. This part of the protein, a homeodomain, binds to DNA and switches other genes on or off. Homeobox genes are therefore regulatory genes.

Question 36

What are hox genes?

Answer 36

Hox genes are one group of homeobox genes that are only present in animals. They are responsible for the correct positioning of body parts. In animals, the Hox genes are found in gene clusters. Mammals have four clusters on different chromosomes. The order in which the genes appear along the chromosome is the order in which their effects are expressed in the organism.

Question 37

How are body plans represented?

Answer 37

Cross sections through the organism showing the fundamental arrangement of tissue layers.

Question 37

How are body plans represented?

Answer 37

Cross sections through the organism showing the fundamental arrangement of tissue layers.

Question 38

What are diploblastic and triploblastic animals?

Answer 38

A diploblastic animal has two primary tissue layers and triploblastic animals have three primary tissue layers.

Question 39

What is a common feature of all animals?

Answer 39

They are all segmented. These segments have multiplied over time and are specialised to perform different functions. Hox genes in the head control the development of mouthparts, and the Hox genes in the thorax control the development of wings, limbs, or ribs.

Question 40

What are somites?

Answer 40

Segments in the embryo from which individual vertebrae and associated structures have all developed. The somites are directed by Hox genes to develop in a particular way depending on their position in the sequence.

Question 41

Describe the three examples of symmetry of animals.

Answer 41

Radial symmetry is seen in diploblastic animals like jellyfish
Bilateral symmetry is seen in most animals and means that they have both left and right sides, and a head and tail.
Asymmetry is seen in sponges.

Question 42

How do mitosis and apoptosis contribute to the shaping of organisms?

Answer 42

Mitosis increases the number of cells leading to growth. Apoptosis removes unnecessary cells, fine-tuning the structure. Also, cells undergoing apoptosis can release chemical signals which stimulate mitosis and cell proliferation leading to the remodelling of tissues.

Question 43

What are the factors affecting the expression of regulatory genes?

Answer 43

Expression of regulatory genes can be influenced by the environment, both internal and external, so if an organism is under stress. Also, drugs may affect the activity of regulatory genes.