Gene Expression

Question 1

What is a mutation?

Answer 1

change to the quantity or the structure of the DNA of an organism

Question 2

What is a gene mutation?

Answer 2

Any change to one or more nucleotide base

Question 3

What is the substitution of bases (mutation)?

Answer 3

• new base substituted = stop coding,
• different codon = different amino acid - tertiary structure different,
• different codon = same amino acid.

Question 4

What is the deletion of bases (mutation)?

Answer 4

• frame shift left - many codons affected (if affecting beginning) or smaller impact (towards the end)

Question 5

What is an insertion mutation?

Answer 5

• extra base becomes inserted in the sequences- frame shift right

Question 6

What is a duplication of bases mutation?

Answer 6

• bases are repeated - frame shift right

Question 7

What is a inversion of bases mutation?

Answer 7

• a group of bases become separated from DNA sequences and rejoin in inverse - affects amino acids sequence produces

Question 8

What is the Translocation of bases mutation?

Answer 8

• DNA sequence one chromosome is separated and joins another DNA sequence on a different chromosome - abnormal phenotype - cancer, fertility issues

Question 9

What are Mutagenic agents?

Answer 9

• increase rate of mutations = high ionising radiation - disrupt DNA structure, Chemicals - alter DNA or transcription

Question 10

What is cell differentiation?

Answer 10

the process through which cells become specialised to perform specific functions

Question 11

What do mutagenic agents do?

Answer 11

disrupt DNA structure, Chemicals - alter DNA or transcription

Question 12

Are all genes expressed in a given cell at one time?

Answer 12

not all genes expressed in a given cell at one time -> as they serve different functions

Question 13

Some genes permanently expressed those gene ….

Answer 13

code for essential processes

Question 14

What are totipotent cells?

Answer 14

• cells that can mature into any body cell, including the placenta -> e.g cells derived at an early stage from a fertilised egg

Question 15

What are the stems and what are different types of stem cells?

Answer 15

• Stem cells - have the ability to divide to form an identical copy of themselves
• Stem cells can be found in: Embryos (early - totipotent), umbilical cord (multi-potent), placenta, Adult stem cells (multipotent)

Question 16

How are genes not expressed?

Answer 16

preventing transcription -> mRNA OR preventing translation

Question 17

What are pluripotent cells?

Answer 17

differentiate into almost any cell (embryonic) - not the placenta

Question 18

What are multipotent cells?

Answer 18

limited number of specialised cells (stem cells in bone marrow - blood cells)

Question 19

What are unipotent cells?

Answer 19

• only differentiate in one cell (cardiomyocytes - heart tissues)
• genetically altered -> to acquire characteristics of embryonic -> include genes and transcriptional factors

Question 20

What are IPS cells?

Answer 20

• capable of self-renewal - potentially divide indefinitely = more pluripotent cells -> grow tissues that are damaged

Question 21

What are transcriptional factors?

Answer 21

complementary to the specific base sequence of DNA-> region of DNA begins transcription = mRNA that can attach to the ribosome in the cytoplasm

Question 22

What is oestrogen?

Answer 22

-Steroid hormones that act as transcription factors

Question 23

How does oestrogen work?

Answer 23

• Diffuse into membrane -> binds to a receptor site on transcription factor -> DNA binding site changes (tertiary structure change) -> complimentary so can now bind to DNA -> transcription factor enter nucleus through nuclear pore -> bind to specific base sequence in DNA -> transcription occurs

Question 24

What is the effect of small interfering RNA on gene expression?

Answer 24

• An enzyme cuts large double-stranded molecules of RNA into smaller sections called (siRNA) -> ½ of siRNA strands combine with an enzyme
• The siRNA molecules guide the enzyme to a mRNA molecule by pairing up its bases with complementary ones on a section of the mRNA
• Once in position, the enzyme cuts mRNA into smaller sections -> no longer capable of being translated into polypeptide -> which means the gene has not been expressed

Question 25

What is a proto-oncogene?

Answer 25

- code for both cell surface receptors and intercellular proteins -> stimulate a cell to divide when growth factors attach to a protein.

Question 26

What happens if a proto-oncogene mutates into an oncogene?

Answer 26

it becomes permanently activated (switched on) for 2 reasons: - The receptor protein on the cell-surface membrane is permanently activated so that cell division is switched on even in the absence of growth factors - The oncogene may code for a growth factor that is then produced in excessive amounts, again stimulating excessive cell division

Question 27

What are tumour suppressor genes?

Answer 27

slow down cell division, repair mistakes in DNA - inhibit cell proliferation or cause apoptosis (opposite role from proto-oncogenes)

Question 28

What happens if tumour suppressor genes become mutated?

Answer 28

it is inactivated - drops inhibiting cell division and cells can grow out of control

Question 29

What does hypermethylation result in ?

Answer 29

- Hypermethylation in the promoter region of tumour suppressor gene - tumour suppressor gene inactivated - transcription inhibited - tumour suppressor gene is silenced - increased cell division - formation of tumour

Question 30

What are the links between oestrogen and cancer?

Answer 30

more oestrogen -> tumour development -> white blood cells drawn to tumour -> increase oestrogen conc

Question 31

What is epigenetics?

Answer 31

environment factors affecting genetic inheritance - influenced by Lamark

Question 32

What is an epigenome?

Answer 32

DNA + Histones are covered in chemicals (AKA tags)

Question 33

What is epigenome silencing and how does it occur?

Answer 33

inactive genes are tightly packed = less accessible - so they are not switched on

Question 34

What is acetylation?

Answer 34

a process whereby an acetyl group is transferred to a molecule

Question 35

What is Deacetylation

Answer 35

acetyl group is removed from molecules

Question 36

What happens when acetylation is decreased?

Answer 36

increases the positive charges of histones - increases attraction to phosphate groups of DNA -> DNA + histones association stronger -> not accessible by transcription factors -> cannot initiate mRNA production -> gene switched off

Question 37

What is methylation and how does it inhibit transcription of genes?

Answer 37

addition to methyl group (added to cytosine) - normally inhibits the transcription of genes by: - Preventing the binding of transcriptional factors of the DNA - Attracting proteins that condense the DNA-histone complex, making inaccessible to transcriptional factors

Question 38

What is the human genome?

Answer 38

consists of over 3 billion base pairs organised into around 20,000 genes -> this was facilitated by bioinformatics (the science of collecting and analysing complex biological data)

Question 39

What is a proteome?

Answer 39

all the proteins produced by genome /(in a given type of cell or organism at a given time under specified conditions.)

Question 40

How does epigenetics work?

Answer 40

An environmental signal stimulates proteins to carry its message into the cell -> passed through proteins in the nucleus -> specific protein attaches to a specific sequence of bases on DNA -> 2 possible effects: Acteylation of histone = Activation or inhibition of genes, methylation of Dna by attracting enzymes that can add or remove methyl groups