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biology paper 2 > 3.8.2 gene expression > Flashcards

3.8.2 gene expression Flashcards

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1
Q

what gene mutation causes substitution?

A

nucleotide is substituted for another

less damaging effect on the polypeptide
however can cause a severe change

eg swapping an A for a T in a gene for haemoglobin causes a serious disease called sickle cell anaemia

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2
Q

what is a silent mutation?

A

due to the degenerate nature of the genetic code, not all mutations result in a change to the amino acid sequence of the encoded polypeptide

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3
Q

what’s the difference between conservative and non-conservative?

A

conservative = mutation leads to a functional protein

non-conservative = mutation leads to a non-functional protein

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4
Q

what gene mutation causes addition?

A

extra nucleotide may be added

new forms of alleles arise from changes to existing alleles

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5
Q

what gene mutation causes deletion?

A

nucleotide is removed

the portion of a nucleotide being changed is called a point mutation

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6
Q

what gene mutation causes duplication?

A

in chromosomal duplications, extra copies of a chromosomal regions are formed

results in different numbers of genes within that area of the chromosome

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7
Q

what is translocation?

A

a chromosome abnormality caused by rearrangement of parts between homologous chromosomes

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8
Q

what is a frame shift?

A

causes all further amino acids to be changed

may also cognate the position of start and stop codons

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9
Q

what are mutagens?

A

mutations can occur naturally but their appearance increases by mutagens

  • X-rays
  • high energy radiation eg GAMMA
  • chemicals in cigarette smoke
  • chemicals in caffeine
  • UV light
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10
Q

what are the effects of mutations?

A

many proteins are coded for by genes which regulate metabolic pathways

causes change in active site

enzyme activity is slowed or stopped altogether

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11
Q

what are proto-oncogenes?

A

the rate of cell division is controlled by proto-oncogenes
these stimulate cell division

a specific proto-oncogene needs to be switched on by a growth factor to cause a cell to grow and divide

most of the tumour suppressor genes slow cell division down by inhibiting the proto-oncogenes

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12
Q

what are the effects of mutated proto-oncogenes and tumour suppressor gene?

A

a mutated proto-oncogene (oncogene) stimulates cells to divide too quickly

a mutated tumour suppressor gene is inactivated, allowing the rate of all cell division to increase

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13
Q

what are stem cells?

A

stem cells retain the ability to divide and differentiate into a range of specialised types

all stem cells are undifferentiated

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14
Q

what are the two types of stem cells?

A
  1. embryonic stem cells = divide and differentiate into specialised embryonic tissues
  2. adult stem cells = involved in repair and placement of specialised cells
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15
Q

what are the 4 potentecny of cells?

A
  1. totipotent = can make all cell types
    zygotes and early embryo cells
  2. pluripotent = capable of producing all cells derived from a particular germ layer
    ectoderm, endoderm and mesoderm
  3. multipotent = can make a restricted range of related cell types
    haemopoietic stem cells make red cells, white cells and platelets
  4. unipotent = able to make one cell type
    cardiomyoblasts can only differentiate into cardiomyocytes
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16
Q

what are embryonic stem cells?

A

stem cells are taken from embryos
in the morula stage = totipotent

inner mass of a blastocyst = pluripotent

development suggests that it can be used for treatment eg Parkinson’s

use is controversial and research is tightly regulated

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17
Q

what are adult stem cells?

A

can divide and differentiate

multipotent and usually referred to where they are found
eg haemopoietic stem cells in bone marrow

successfully used to treat leukaemia

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18
Q

how do stem cells differentiate?

A

in unicellular and simple multicellular organisms each cell is capable of performing all functions

not so in more complex organisms

derived from mitosis and contain the same instructions

once differentiated they lose ability to divide and totipotency

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19
Q

what are IPS?

A

induced potipotent stem cells = turning skin cells into embryonic stem cells

reprogramming skin cells by adding four proteins/factors

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20
Q

what are transcription factors?

A

they are proteins which move in from the cytoplasm and bind to DNA at specific sites called promoters
found near the start of a target gene

enable RNA polymerase to attach to the start of the gene and begin transcription

some are activators = help RNA polymerase to bind and active transcription

some are repressors = decrease the rate of transcription because they are slow or prevent RNA polymerase from binding

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21
Q

what is the effect of oestrogen on the regulation of transcription and translation?

A

oestrogen is a steroid hydrophobic hormone that can diffuse through the plasma membrane of cells

once in the cytoplasm it can diffuse into the nucleus where it can bind to a oestrogen receptor (transcription)

binding changes shape of oestrogen receptor forming OESTROGEN RECEPTOR COMPLEXES

complex can bind to promoter region of genes
acts as an activator, RNA polymerase binds so transcription begins

22
Q

describe the process of oestrogen as a regulator

A
  1. oestrogen diffuses through the cell membrane into the cytoplasm
  2. oestrogen diffuses into cell nucleus
  3. oestrogen binds to a receptor, ER-alpha (a transcription factor held in a protein complex to inactivate/inhibit it)
  4. ER-alpha receptor changes shape
  5. ER-alpha oestrogen receptors leaves its protein complex and attaches to the promoter region of the target gene
  6. Other co-factors are attracted and also binds to the promoter region
  7. RNA polymerase begins transcription of the target gene
23
Q

what is the effect of RNA interference - RNAi on transcription and translation

A

gene expression can be affected by small RNA molecules that stop mRNA from being translated

siRNA (small interfering RNA) found in animals and plants
short double stranded RNA is formed when this folds back on itself by complementary base pairing to make a hair-pin like double stranded molecule

miRNA (micro interfering RNA) found in mammals

24
Q

describe siRNA (small interfering RNA)

A

siRNA are unwound and single strands of siRNA are formed

associated with these single strands are proteins/enzymes

single strand of siRNA will bind to complimentary mRNA

associated proteins will cut the mRNA into fragments

no transcription = no protein formed

25
Q

where do transcription factors move from and to?

A

cytoplasm into nucleus

26
Q

what are transcription factors made from?

A

proteins

27
Q

where do transcription factors bind?

A

to promoters at the start of a gene or DNA

28
Q

why are some transcription factors called activators?

A

they increase the rate of transcription

29
Q

why are some transcription factors called repressors?

A

they decrease the rate of transcription

30
Q

describe how transcription factors in the synthesis of proteins

A

bind to gene/DNA
at a specific place

stimulate/prevent transcription
either turn on or off the gene

31
Q

explain how an activated oestrogen receptor affects a target cell

A

binds to a transcription factor
then to a promotor

stimulates RNA polymerase
which increases transcription

32
Q

why may siRNA be useful in treating some diseases?

A

some diseases are genetic and caused by mutations

siRNA will stop translation or the protein being produced

33
Q

what is epigenetics?

A

how environmental influences affect genetic inheritance

34
Q

what are histones?

A

these are highly alkaline proteins found in eukaryotic cells nuclei that package and order the DNA into structural units called nucleosome

histones are a group of basic protein that associate with DNA and helps the DNA to condense it into chromatin

35
Q

what are histones covered in?

A

histones are covered in chemicals referred to as tags

tags = epigenome

determines the shape of the histone = DNA complex

accumulation of environmental signals received in life = chemical tags
from the moment of contraception

36
Q

what is the histones structure?

A

inactive genes can be tightly wrapped and become inaccessible
genes are not read (epigenetic silencing)

active genes are looser and are more easily read and transcribed

DNA = fixed
histone/epigenome = flexible

37
Q

describe the ditch famine

A

1994-1995

the children of the women who were pregnant during the famine were smaller as expected

when this generation, had children they were smaller than expected

38
Q

what are the epigenetic signals?

A

stimulate proteins to chaperone it’s messages to the cell

signals are chaperoned through a variety of proteins and makes it into the nucleus

has two effects

39
Q

what is the DNA histone complex?

A

weak association with histone and loosely packed DNA

DNA is accessible by transcription factors = mRNA can be made

strong association with histone and is tightly packed

not accessible by transcription factors

40
Q

what is acetylation?

A

leads to activation or inhabitation

acetylated chromatin = open and transcriptionally active

deacetylated chromatin = compact and transcriptionally repressed

41
Q

what is decreased acetylation?

A

acetylation = acetyl group is transferred to a molecule

group donating is acetyl coenzyme A

deacetylation = acetyl group is removed

increases the positive charges on histones and increases their attraction to the negative phosphate groups

association between histone and DNA is stronger so no transcription

42
Q

what is methylation?

A

methylation of DNA by attraction of enzymes that can add and remove methyl groups

the most widely characterised DNA methylation process is the covalent
addition of the methyl group at the 5-carbon of the cytosine ring

these methyl groups project into the major groove of DNA and inhibit transcription

43
Q

what is increased methylation?

A

methylation = addition of methyl groups to molecules

usually covalent addition of the methyl group at the 5-carbon of the cytosine ring
resulting in 5-methylcytosine (5th base of DNA)

methyl projects into the major groove of DNA and inhibit transcription

44
Q

what is cell division in cancer?

A

cell division is tightly controlled by genes

tumour suppressor genes inhibit cell division

proto-oncogenes stimulate cell division

ensure cells divide at a rapidly constant rate

45
Q

describe malignant tumours

A

Can also grow to a large size

Grow rapidly

The cell nucleus is often larger and appears darker due to an abundance of DNA

Cells become de-differentiated (unspecialised)

Cells do not produce adhesion molecules and so they tend to spread to other regions of the body, a process called metastasis, forming secondary tumours

Tumours are not surrounded by a capsule and so can grow finger-like projections into the surrounding tissue

More likely to be life-threatening, as abnormal tumour tissue replaces normal tissue

Often have systemic (whole body) effects such as weight loss and fatigue

Removal usually involves radiotherapy and/or chemotherapy as well as surgery

More frequently reoccur after treatment

46
Q

describe benign

A

Can grow to a large size

Grow very slowly

The cell nucleus has a relatively normal appearance

Cells are often well differentiated (specialised)

Cells produce adhesion molecules that make them stick together and so they remain within the tissue from which they arise = primary tumours

Tumours are surrounded by a capsule of dense tissue and so remain as a compact structure

Much less likely to be life-threatening but can disrupt functioning of a vital organ

Tend to have localised effects on the body

Can usually be removed by surgery alone

Rarely reoccur after treatment

47
Q

what are proto-oncogenes?

A

normally only switched on when growth factors are detected by protein receptors on the CSM

causes relay proteins in the cytoplasm to switch these genes on

48
Q

what are oncogenes?

A

mutation can cause proton-oncogenes to mutate into oncogenes

genes become permanently switched on, even in the absence of growth factors that would normally stimulate appropriate cell division

receptor on CSM could be permanently activated

growth factor is produced in excessive amounts

49
Q

what are tumour suppressor genes?

A

slow down cell division

repair mistakes in DNA

instructs apoptosis = programmed cell death

50
Q

what are the two types of tumour suppressor genes?

A
  1. wild type p53 = transcriptional regulation of genes that mediate growth-suppression, apoptosis and DNA repair
  2. mutant p53 = transcriptional regulation of genes that media proliferation, drug-resistance, survival and metastasis
51
Q

describe abnormal methylation of tumour suppressor genes

A

inactivated tumour suppressor gene

transcription of promoter region inhibited

tumour supressor gene silenced
leads to increased cell division and tumour formation

52
Q

describe oestrogen production

A
  1. acts on a gene that controls cell division
  2. gene is activated
  3. tumour growth develops

oestrogen can cause proto-oncogenes in breast tissue to mutate to oncogenes

biology paper 2 (12 decks)

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