The Control of Gene Expression

Question 1

What does substitution mutation involve?

Answer 1

When one nucleotide in a section of DNA molecule is replaced by another nucleotide that has a different base.

Question 2

What could be consequences of a substitution mutation?

Answer 2

• substitution results in a different aa being produced meaning the protein may not function properly
• results in a stop codon being transcribed meaning polypeptide coding is stopped prematurely
• substitution means nothing changes as the genetic code is degenerate

Question 3

What happens in a deletion mutation?

Answer 3

Involves the loss of a nucleotide base from a DNA sequence. The polypeptide chain is often different due to the frame shift and will change how most of the codons are being read
Less likely to have an effect if it occurs at the end of a sequence

Question 4

What happens in addition mutation?

Answer 4

When a extra base is added into the sequence and this also causes a frame shift causing the codons after to change

Question 5

What does inversion mutation involve?

Answer 5

Involves a group of bases becoming deprecated from the DNA sequence and rejoining in the same position but in inverse order, so instead of AUG, it’s GUA

Question 6

What does duplication mutation involve ?

Answer 6

One or more of the bases are repeated which produces frame shift to the right

Question 7

What does translocation mutation involve?

Answer 7

Group of bases become separated from the DNA sequence in one chromosome and becomes inserted into DNA sequence of another chromosome

Question 8

What are mutagenic agents?

Answer 8

Something that can effect the rate of gene mutation

Question 9

Examples of mutagenic agents

Answer 9

UV light, X rays, alpha and beta radiation and chemicals such as mustard gas and nitrogen gas and cigarette smoke and Benzene (inactivates tumour suppressor gene)

Question 10

What are stem cells?

Answer 10

Cells that have the potential to differentiate into different specialised cells

Question 11

What are stem cells properties?

Answer 11

Self renewal- the ability to go through numerous cycles of mitosis while remaining undifferentiated
Potency- the capacity to differentiate into specialised cell types

Question 12

What are totipotent stem cells?

Answer 12

Found in embryos and can differentiate into all 216 or so cell types

Question 13

What are pluripotent stem cells?

Answer 13

Found in the embryos and differentiate into almost every cell types-ex. includes embryonic stem cells and fetal stem cells

Question 14

What are multipotent stem cells?

Answer 14

Found in adults and can differentiate into a limited number of specialised cells.

Question 15

What are unipotent cells?

Answer 15

Can only differentiate into a single type of cell. Derived from multi-potent stem cells and are made in adult tissue (fetal stem cells)

Question 16

What are induced pluripotent stem cells?

Answer 16

These are unipotent stem cells from specialised animal cells by genetically altering them using INDUCING GENES and transcription factors to acquire characteristics of EMBRYONIC STEM CELLS

Question 17

What is therapeutic cloning?

Answer 17

Technique used to extract or produce and grow stem cells for the purpose of treating human disorders. For example; creating new skin for burn victims

Question 18

What are the role of transcription factors?

Answer 18

Protein that binds to the promotor region of a gene to either promote or inhibit transcription

Question 19

How do activators (transcription factors) work?

Answer 19

They move from the cytoplasm to the nucleus and bind to start of their target genes and helping RNA polymerase bind to the target gene and thus activating transcription

Question 20

How do repressors (transcription factors) work?

Answer 20

An inhibitor molecule can bind to a transcription factor where it binds to DNA and blocks that DNA polymerase so transcription is deactivated and gene is not transcribed

Question 21

How does oestrogen aid the action of a transcription factor?

Answer 21

Oestrogen binds to a complimentary active site on the transcription factor molecule called ERalpha.
The transcription factor as a result changes shape and thus releases the inhibitor molecule from the binding site
The transcription factor can now enter the nucleus and bind to a specific region of DNA where it will stimulate transcription

Question 22

What is epigenetics?

Answer 22

heritable changes in gene function without changing the base sequence of DNA

Question 23

What is an epigenome?

Answer 23

DNA and histones are covered in chemical which forms a second layer known as the epigenome. Determines the shape of the DNA-histone complex

Question 24

Examples of the effect of the epigenome?

Answer 24

It can keep inactive genes in a tightly packed arrangement- so it ensures they cannot be read
OR it unwraps active genes so DNA is exposed and can easily be transcribed.

Question 25

What does acetylation of histones do ?

Answer 25

This increases the +ve charges on the histones increases their attraction to the phosphate group of DNA the DNA-histone association is stronger makes DNA inaccessible to transcription factors so the gene is switched off

Question 26

What does methylation of DNA do?

Answer 26

It's added to the cytosine bases and it inhibits transcription preventing the binding of transcription factors to DNA Prevents RNA polymerase from binding So protein synthesis is prevented

Question 27

What's the second thing that methylation of DNA can cause?

Answer 27

Methyl groups can attract proteins that condense the DNA-histone complex making DNA inaccessible to proteins

Question 28

Examples of the use of epigenetics?

Answer 28

Can be used in the diagnostic testing of cancers, arthritis and brain disorders. This can identify the level of DNA methylation and histone acetylation

Question 29

How does small interfering RNA work (siRNA) ?

Answer 29

Enzyme cuts the large double stranded molecules of RNA into siRNA. One of these strands combines with an enzyme to form a siRNA-protein complex. siRNA complex is moved to mRNA pairs with complementary bases then cuts it into smaller sections

Question 30

What is the effect of the siRNA attaching to the mRNA?

Answer 30

Cuts mRNA to smaller sections; mRNA is no longer able to be translated into polypeptide; gene is not expressed

Question 31

Similarities between benign and malignant tumours?

Answer 31

They can grow to a large size and can add pressure to blood vessels when they grow

Question 32

Differences between benign and malignant tumours?

Answer 32

malignant undergo metastasis, benign tumours do not due to adhesion molecules Benign have a capsule surrounding them, malignant don't. Benign tumours can be removed by surgery alone whilst malignant tumours require chemotherapy as well

Question 33

What are proto-oncogenes?

Answer 33

These stimulate a cell to divide when growth factors attach to a protein receptor on the CSM. These activate genes that cells to divide.

Question 34

How can oncogenes be permanently activated?

Answer 34

Two ways: Receptor protein is permanently activated even in absence of growth factors or oncogene codes for growth factors that is produced in excessive amounts

Question 35

What is the effect of permanent activation of oncogenes?

Answer 35

uncontrollable cell division and as a result cancer develops

Question 36

What are tumour suppressor genes?

Answer 36

These slow down cell division, repair mistakes in DNA and tell cells when to die DNA cannot be repaired- apoptosis

Question 37

What happens if tumour suppressor genes becomes mutated?

Answer 37

Gene is inactivated it stops inhibiting cell division leads to uncontrollable cell division

Question 38

How does hypermethylation of the tumour suppressor gene lead to cancer?

Answer 38

More methyl groups are added to promotor region and prevents transcription Therefore protein is not made and tumour suppressor gene is not expressed Therefore promotor region of tumour suppressor gene is inactivated This gene inactivation leads to uncontrollable cell division

Question 39

How does oestrogen concentrations cause breast cancer?

Answer 39

if the gene that oestrogens acts on a gene and removes one that controls cell division and growth, the gene will be inactivated and would produce a tumour

Question 40

where do multipotent stem cells usually develop?

Answer 40

usually develop into the stem cells in the bone marrow

Question 41

Describe the process of genetic fingerprinting (6 points)

Answer 41

1. DNA sample is put through PCR to make large sample 2. Sample is cut R-endonuclease 3. Gel electrophoresis seperates DNA fragments by length 4. Southern Blotting technique used 5. DNA is made single stranded using chemicals 6. DNA probe is attached which has complimentary base sequence to tandem repeats 7. Every person has unique DNA fingerprint

Question 42

How does PCR work?

Answer 42

1. Heat to 95c to break H bonds between DNA strands to separate the two strands 2. Mixture is cooled to 55c causing primers to bind to complimentary bases 3. Increase temp to 72c to allow DNA polymerase to add complementary nucleotides 4. Cycle is repeated to 25-30 times

Question 43

What is a DNA probe?

Answer 43

Short, single stranded length of DNA with a label attached (radioactive or florescent)

Question 44

Purpose of DNA probes

Answer 44

To identify particular alleles of genes

Question 45

What is the purpose of primers ?

Answer 45

Provide starting sequences for DNA polymerase to begin copying Prevents two separate strands for rejoining

Question 46

What is DNA hybridisation?

Answer 46

The binding of a section of DNA or RNA with a single stranded section of DNA (usually a DNA probe) with complimentary bases

Question 47

Effects of methylation on gene expression

Answer 47

Prevents binding of transcription factors Prevents RNA polymerase from binging Prevents mRNA from being made No translation occurs