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Biology-Corinna > 20.Gene Expression > Flashcards

20.Gene Expression Flashcards

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1
Q

How does oestrogen affect gene transcription

A
  • lipid soluble molecule, diffuses through phospholipid cs membrane
  • once in cytoplasm, oestrogen bind with site on receptor molecule of transcription factor
  • by binding to site, oestrogen changes shape of DNA binding site on transcription factor
  • transcription factor can now enter nucleus through nuclear pore and bind to specific base sequence on DNA
  • RNA polymerase can now bind and transcribe
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2
Q

Why do some gene mutations not result in changed amino acid sequence

A

Degenerate

Multiple codons encode for same amino acid some some base substitution may not change amino acid coded for

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3
Q

What are the types of gene mutation

A 
Addition of bases
Duplication of bases
Inversion of bases
Translocation of bases
Base substitution 
Deletion of bases
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4
Q

What is epigenetics

A

Environmental factors that can alter gene expression and make heritable changes without altering base sequence of DNA

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5
Q

What is epigenome

A

DNA and histones and chemical tags

Determines the shape of DNA histone complex and keeps inactive genes tightly packed arrangement therefore cannot be read-known as epigenetic silencing

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6
Q

What is base substitution

A
  • where a single nucleotide in a section of DNA molecule is replaced by another nucleotide that has a different base
  • three possible consequences:may form stop codon final protein will be significantly different, different amino acid protein differ in shape not function properly, same amino different codon same protein shape
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7
Q

what is base deletion

A

loss of a single nucleotide base, creates a frame shift therefore all bases move to left by one letter, meaning rest of codons are now read differently, polypeptide will be different leading to non-functional protein

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8
Q

what is addition of bases

A

extra base is inserted into sequence, creating frame shift to right, whole sequence of triplets is altered, polypeptide different from one produced by non-mutant gene

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9
Q

what is duplication of bases

A

one or more bases are repeated creating frame shift to the right

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10
Q

what is inversion of bases

A

group of bases become separated from DNA sequence and rejoin in reverse order but in same place, affecting the amino acid coded for

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11
Q

what is translocation

A

combination of addition and deletion, group of bases separated from DNA sequence and are inserted into sequence of another chromosome, often have significant effect on gene expression

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12
Q

what are the causes of gene mutations

A
  • spontaneous during DNA replication and is permanent

- basic mutation rate increased by mutagenic factors

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13
Q

what are some mutagenic factors

A

Ionising radiation; alpha beta particles and x-rays and UV light disrupt structure of DNA

  • chemicals such has nitrogen dioxide alter structure of DNA or interfere with transcription
  • benzopyrene inactivates tumour suppressor gene TP53 leading to cancer
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14
Q

how can mutagenic factors cause damage

A
  • benzopyrene adds large group to guanine so unable to pair with cytosine, DNA polymerase inserts any other bases
  • ionising radiation produce high reactive agents called free radicals in cells, alter shape of bases, DNA polymerase no longer act on them
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15
Q

what is totipotency

A

cells which can mature into any cell, from a fertilised egg

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16
Q

how are genes prevented from expressing themselves?

A

preventing transcription and so preventing the production of mRNA or preventing translation

17
Q

how do cells lose their totipotency

A

when they mature and differentiate into specialised cells

18
Q

what are stem cells

A

undifferentiated dividing cells taht occur in adult animal tissues and need to be constantly replaced so they self renew

19
Q

where do stem cells originate from

A
  • embryonic stem cells
  • umbilical cord blood stem cells
  • placental stem cells
  • adult stem cells (specific to particular tissue or organ within which they produce the cells to maintain and repair the tissues throughout organism life)
20
Q

what are the types of stem cells

A

totipotent-early stages of emryo/zygote differentiate into any specialised cell
pluripotent-in embryos eg embryonic stem cells can differentiate into almost any type of specialised cells
multipotent-adults, differentiate into limited number of specialised cells
unipotent-only differentiate into single type of specialised cell

21
Q

what are induced pluripotent stem cells

A

type of pluripotent stem cell derived from unipotent stem cells, unipotent cell can be any body cell and is genetically altered in a lab to make them acquire the characteristics of embryonic stem cells, the genetic altering includes turning on genes which retain same genetic information that was in embryonic stem cells

22
Q

pluripotent cells in treating human disorders

A 
regrow tissues
skin grafts
skeletal muscle cells
nerve cells
skin cells
23
Q

what is chromatin

A

DNA-histone complex

24
Q

effect of RNA intereference on gene expression

A

small double stranded sections of siRNA

  • enzyme buts large double stranded molecule of RNA into smaller sections called siRNA
  • one of two strands of siRNA combines with an enzyme
  • siRNA molecule guides enzyme to mRNA by pairing up its bases with complimentary ones on section of mRNA
  • enzyme cuts mRNA into smaller sections
  • mRNA no longer capable of being translated into polypeptide
  • gene not expressed and been blocked
25
Q

what is a benign tumour

A

non-cancerous tumour of cells

26
Q

what is a malignant tumour

A

cancerous tumour of cells

27
Q

what are differences between benign and malignant tumours

A

grow to large size/grow to large size
grow slowly/grow fast
normal appearance of nuclei/abnormal nuclei
cells well differentiated/cells de-differentiated
produce adhesion molecules/no adhesion molecules
no metastasis/metastasis
surrounded by capsule/no capsule, finger like projections
less life threatening/more life threatening
localised effects/systematic effects eg weight loss
removed by surgery alone/radio or chemo therapy

28
Q

proto-oncogenes

A
  • stimulate cells to divide when growth factors attach to a protein receptor on its cell surface membrane
  • his activates genes that cause DNA to replicate and cell to divide
  • if mutates into oncogene it can be permanently activated
  • occur if: receptor protein is permanently activated, oncogene code for growth factor which is produced in excessive amounts
29
Q

tumour suppressant gene

A
  • slow down cell division, repair mistakes in DNA and stimulates cells to do apopstasis eg P53
  • mutated means inactive
  • stops inhibiting cell division and cells grow out of control
30
Q

abnormal methylation of tumour suppressor genes

A
  • hypermethylation occur in specific region of tumour suppressor gene
  • tumour suppressor gene being inactivated
  • transcription of promoter regions of tumour suppressor gene is inhibited
  • tumour suppressor gene switched off
  • inactivation leads to increased cell division and formation of tumour
31
Q

What is acetylation

A

When acetyl groups bind to histone-dna complex
This spreads out the chromatin
Making more accessible for transcription
Gene is turned on
Acetyl group comes from acetyl coenzyme A

31
Q

What is methylation

A

Addition of methyl group to cytosine bases
Prevents binding of transcriptional factors to dna
Attracts proteins that condense DNA-histone complex
it’s inaccessible to transcription factors

31
Q

What’s decreased acetylation

A

Removal of acetyl group
Increases positive charges on histones
Increased attraction to phosphate groups of DNA
Association between DNA and histones is greater, not accessible to transcription factors
Gene switched off

Biology-Corinna (22 decks)

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