Topic 8 last

Question 1

What is a mutation?

Answer 1

• A change in the DNA base sequence
• Occur in somatic cells or gametes

Question 2

6 types of mutation

Answer 2

• Substitution
• Deletion
• Addition
• Inversion (180 degrees))
• Duplication
• Translocation (inserted at different position in the genome)

Question 3

Why might a mutation not have effect upon the phenotype?

Answer 3

• Some take place within introns
• Some take place in non-coding regions between genes
• Genetic code is degenerate so the sequence of encoded amino acids may still be the same as the new codon may code for the same amino acid.
• May change the amino acid but have no effect on the tertiary structure as the same bonds are formed.

Question 4

Types of mutagenic processes

Answer 4

• Mutagenic agents increase the rate of mutations
• Base Analogs substitute for a base during DNA replication, which changes the base sequence in the new DNA.
• Some chemicals may delete and alter bases
• Radiation may alter structure of DNA causing problems during replication.

Question 5

2 key properties of stem cells

Answer 5

• The ability to divide
• Ability to differentiatte

Question 6

Different type of stem cells

Answer 6

• Totipotent stem cells divide and differentiate into any type of body cell
• Pluripotent stem cells are descendants of totipotent cells and can differentiate into any type of body cell except those that make up the placenta.
• Multipotent stem cells differentiate into a limited number of types of body cells
• Unipotent cells only differentiate into 1 type of cell

Question 7

What are the uses of stem cells?

Answer 7

• Pluripotent stem cells divide into unlimited numbers and can be used to treat human disorders
• Unipotent cardiomyocytes could develop into new heart tissue
• iPS cells - pluripotent cell that are made by repogramming adult somatic cells. They are made to express a series of transcription factors that are normally associated with pluripotent stem cells.

Question 8

Issues with stem cells

Answer 8

• An embryo has the ability to form a human
• Stem cells may multiply out of control in the body to form tumours.

Question 9

Outline the process of regulating transcription and translation?

Answer 9

• Transcription factors move from cytoplasm into the nucleus
• Here they bind to specific promoter regions near the start of their target genes
• Activators increase the rate of transcription, making it easier for RNA polymerase to bind to the start of target genes
• Repressors decrease the rate of transcription making it harder for RNA polymerase to bind to the start of the target gene.

Question 10

The role of oestrogen in initiating transcription

Answer 10

• Since oestrogen is a steroid hormone which is a lipid, they can diffuse through the phospholipid bilayer of the cell surface membrane.
• In the cytoplasm, oestrogen binds to an oestrogen receptor to form an oestrogen-oestrogen receptor complex.
• This passes into the nucleus where it acts as a transcription factor which binds to the promoter region of a specific gene.
• The oestrogen-oestrogen receptor complex acts as an activator and repressor of different genes.

Question 11

What is epigenetics? (outline everything)

Answer 11

• Heritable changes in gene function without changes to the base sequence of DNA.
• These changes are caused by changes in the environment that inhibit transcription.
• Increased methylation involves methyl group becoming attached to the DNA coding for a gene, attaching at a CpG site, changing the DNA structure, making it harder for transcription factors/RNA polymerase to bind to promoter regions.
• Decreased acetylation of associated histones
• Acetyl groups reduce attraction between DNA and histones so chromatin is ‘relaxed’ making it easier for transcriptional machinery to bind to DNA so increases rate of transcription.

Question 12

RNA interference

Answer 12

• Translation of the mRNA produced from target genes can be inhibited by RNAi
• Small interfering RNA is short, double-stranded RNA which associated with proteins where
  1) the double strand is separated into 2 strands
  2) One strand combines with a protein
  3) RNA-protein complex binds to an mRNA strand that is complementary to the siRNA strand
  4) Protein cuts the mRNA into fragments
  5) The processing body degrades fragments
  6) prevents translation

Question 13

Differences between benign and malignant?

Answer 13

BENIGN:
- Slow growth
- Cells are specialised
- Do not invade neighbouring tissue but can cause blockages and put pressure on other organs

MALIGNANT:
- Fast growth
- Cells are undifferentiated
- Cells break off and spread to other parts of the body via the bloodstream or lymphatic system.
- Invade and destroy surrounding tissues

Question 14

Role of tumour suppressor genes and oncogenes

Answer 14

• Tumour suppressor genes code for proteins that stop cells dividing or cause apoptosis (cell death)
• If a mutation happens in tumour suppressor genes then cells divide uncontrollably
• Hypermethylation causing tumour suppressive protein to not be synthesised.
• Proto-oncogenes - code for proteins that stimulate cell division
• If a mutation occurs in a proto-oncogene then the gene can become overactive and cells divide uncontrollably.
• It can also be caused hypomethylation as there is increased production of proteins that encourage cell divison.

Question 15

How can mutations be prevented from becoming tumours?

Answer 15

• DNA repair mechanisms work
• Cells with the mutation may be detected by the immune system and are destroyed.

Question 16

What is the link between oestrogen and cancer?

Answer 16

• Increased oestrogen levels are associated with higher risks of cancer which may cause increased activation of proto-oncogenes
• Fat cells tend to produce more oestrogen after meopause and with more cells, there is more oestrogen production and the tumour grows even faster.
• White blood cells that are drawn to these tumour cells further increase oestrogen production.

Question 17

What is the genome?

Answer 17

• The complete set of genetic material of an organism so all the DNA in an organism.

Question 18

Why are sequencing projects used?

Answer 18

• To determine evolutionary relationships between organisms.

Question 19

How can scientists use sequencing projects for simpler organisms?

Answer 19

• Simple organisms such as bacteria and fruit flies do not have introns so all DNA is coding.
• DNA is shorter and has no histones so the DNA is more accessible.
• Easier to determine proteome from genome
• Indentifies potential antigens on the surface of bacteria to help develop vaccines.

Question 20

Why is sequencing projects in more complex organisms more difficult than simpler organisms.

Answer 20

• It is harder due to introns, regulatory genes and non coding multiple repeats.

Question 21

What is the recombinant DNA technology?

Answer 21

• Involves the transfer of fragments of DNA from one organism or species to another.
• This works due to the universal code as transferred DNA can be translated within cells of the recipient organism.

Question 22

How do you use reverse transcriptase to produce DNA fragments

Answer 22

1) Reverse transcriptase enzyme
- mRNA for a specific polypeptide is isolated from cell and mixed with free DNA nucleotides and reverse transcriptase.
- Reverse transcriptase uses mRNA as a template to produce complementary DNA, which is a double stranded copy of the required gene.
- mRNA is useful as there’s lots of mRNA of a gene and easier to obtain.

Question 23

How do you use restriction endonucleases to produce DNA fragments

Answer 23

1) Active site of restriction enzyme is complementary to a specific recognition site on the DNA
- Restriction endonuclease binds to the regonition site and cuts the DNA
- Most restriction endonucleases from sticky ends, reveal unpaired base sequences.
- Vectors transfer DNA into the cell (plasmids or bacteriophages)
- Sticky ends of vectors and fragments are joined by DNA ligase which forms phosphodiester bonds

Question 24

How do you use a gene machine to form DNA

Answer 24

• find the Amino acids of specific polypeptide
• Tells us the mRNA base sequence from which we can determine the DNA base sequence, which acted as a template for it.
• Machine assembles and joins together nucleotides in the desired sequence.

Question 25

Why do we need to amplify DNA fragments?

Answer 25

- To produce sufficient copies to work with.

Question 26

Invivo amplification

Answer 26

- Insertion of recombinant DNA into a host cells - For plasmids, host cell is stimulated to take in the plasmid but if a bacteriphage is the vector, then bacteriophage injects its DNA into the bacterium. - Identification using mark genes which are inserted into the vector together with the required gene. - Marker genes that code for antibiotic resistance or flourescence

Question 27

Invitro amplification (PCR)

Answer 27

- Tests for specific DNA base sequences - Genetic modification or fingerprinting 1) Reaction mixture containing primers, DNA polymerase, DNA fragment, DNA nucleotides. (Primer is a short, single-stranded DNA base sequence that is complementary to the bases at the start of the desired DNA fragment) (Allows DNA polymerase to bind to the start of the fragment) 2)Heat to 95 degrees celcius so DNA denatures as H bonds break. 3) Cool to 50-60 degrees celcius, allowing primers to bind to their complementary bases at the ends of fragments. 4) Heat to 72 degrees so that DNA polymerase can carry out extension of the strands and new complementary strands are formed.

Question 28

What is a DNA probe?

Answer 28

- Short, single stranded sequence of DNA whose bases are complementary to a specific DNA sequence.

Question 29

Why are DNA probes used?

Answer 29

- Screen patients for heritable conditions as you can test for presence of the mutated allele. - Investigate drug responses - Check for health risks

Question 30

How do you produce a gene probe?

Answer 30

- You sequence the allele, produce the probe using a gene machine, then use PCR to produce many probes. - Probe is labelled with a flourescent dye or radioactive isotope and so can be detected. - DNA sample is bound to the bottom of the well - If the sequence complementary to probe is present, binding will happen. - The well is then rinsed to wash away any unbound probes. If target allele is present, the probe will showup.

Question 31

What are VNTRs?

Answer 31

- Variable number tandem repeats which are the same base sequences, repeated many times. - VNTRs are non-coding. - Probability of two individuals having the same number of VNTRs is very low because mutations in coding regions aren;t inheritied.

Question 32

How does genetic fingerprinting work?

Answer 32

1) Sample of DNA is obtained 2) Restriction endonucleases cut out VNTRs and PCR is used to amplify. 3) Incubate with labelled probe such as flurescent dye. 4) Many repeats means longer fragments which are placed on agar gel and separated by electrophoresis. 5) Electrophoresis - Electrical current passed through gel and DNA is attracted to the positively charged opposite end as DNA is negatively charged 6) Longer fragments travel more slowly than shorter ones so the fragments separate which produces a series of bands. 7) Patterns of bands can be compared to another genetic fingerprint to see if we are dealing with the same person.

Question 33

Uses of genetic fingerprinting?

Answer 33

- Determine genetic relationships as VNTrs are inherited from parents and therefore can be used in paternity tests. - Genetic variation within a population - Forensic science - MEdical diagnosis (heritable disorders)