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A Level Biology > 8 Gene Expression > Flashcards

8 Gene Expression Flashcards

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1
Q

substitution of bases

A

a nucleotide in a section of a dna molecule is replaced by another nucleotide that has a different base
three possible consequences:
-formation of one of the three stop codons that mark the end of a polypeptide chain
-formation of a codon of a different AA, meaning that the structure of the polypeptide produced would differ in a single AA
-the formation of a diff codon but one that produces the same AA as before. because the genetic code is degenerate

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2
Q

deletion of bases

A

one deleted base creates a frame shift as the reading frame that contains each three letters of the code has been shifted to the left by one letter
gene is now read in the wrong three base groups and the coded info is altered
most triplets will be diff as well as the AAs they code for
polypeptides will be diff and lead to the production of a non functional protein that would considerably alter the phenotype

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3
Q

addition of bases

A

similar effect to base deletion in that there is a frame shift and the whole sequence of triples becomes altered
frame shift to right not left

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4
Q

duplication of bases

A

one or more bases are repeated

produced frame shift to right

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5
Q

inversion of bases

A

group of bases become separated from the dna sequence and rejoin at the same position but in the inverse order

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6
Q

translocation of bases

A

group of bases becomes separated from the dna sequence on one chromosome and becomes inserted into the dna sequence of a diff chromosome

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7
Q

causes of mutation

A

can arise spontaneously during dna replication

mutagenic agents can inc the basic mutation rate

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8
Q

mutagenic agents

A
  • high energy ionising radiation

- chemicals

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9
Q

Totipotent cells

A

cells which can mature into any body cell
e.g. fertilised eggs
During development, totipotent cells translate only part of their DNA, resulting in cell specialisation.
Totipotent cells occur only for a limited time in early mammalian embryos.

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10
Q

stem cells

A

undifferentiated cells which can keep dividing to give rise to other cell types
originate from various sources in mammals:
-embryonic stem cells
-umbilical cord blood stem cells
-placental stem cells
-adult stem cells

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11
Q

types of stem cells

A

totipotent stem cells
pluripotent stem cells
multipotent stem cells
unipotent stem cells

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12
Q

totipotent stem cells

A

found in the early embryo and can differentiate into any type of cell
occur only for a limited time in early mammalian embryos.

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13
Q

pluripotent stem cells

A

found in embryos and can differentiate into almost any type of cell
can divide in unlimited numbers and can be used in treating human disorders.
have a number of different
uses in repairing damaged tissue
e.g. embryonic stem cells and fetal stem cells

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14
Q

multipotent stem cells

A

found in adults and can differentiate into a limited number of specialised cells
usually develop into cells of a particular type: stem cells in bone marrow can produce any type of blood cell
e.g. adult stem cells and umbilical cord blood stem cells

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15
Q

unipotent stem cells

A

can only differentiate into a single type of cell

derived from multipotent stem cells and are made in adult tissue

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16
Q

induced pluripotent stem cells

A

type of pluripotent cell produced from unipotent stem cells
the unipotent cell may be almost any body cell
these body cells are then genetically altered in a lab to make them acquire the characteristics of embryonic stem cells which are a type of pluripotent cell

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17
Q

principles involved controlling the expression of a gene by controlling transcription

A
  • for transcription to begin the gene is switched on by specific molecules that move from the cytoplasm into the nucleus. these molecules are called transcriptional factors
  • each transcriptional factor has a site that binds to a specific base sequence of dna in the nucleus
  • when it binds, it causes this region of dna to begin the process of transcription
  • mRNA is produced and the info it carries is then translated into a polypeptide
  • when a gene is not being expressed (i.e. it is switched off) the site on the transcriptional factor that binds to dna is not active
  • as the site on the transcriptional factor binding to dna is inactive it cannot cause transcription and polypeptide synthesis
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18
Q

The role of the steroid hormone, oestrogen, in initiating transcription

A
  • oestrogen is a lipid soluble molecule and therefore diffuses easily through the phospholipid portion of the cell surface membranes
  • once inside the cytoplasm, oestrogen binds with a site on a receptor molecule of the transcriptional factor. the shape of this site and the shape of the binding site on the transcriptional factor, which can now bind to dna (it is activated)
  • the transcriptional factor can now enter the nucleus through a nuclear pore and bind to specific base sequences on dna
  • the combination of the transcriptional factor with dna stimulates transcription of the gene that makes up the portion of dna
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19
Q

epigenetics

A

involves 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 by:
-increased methylation of the DNA or
-decreased acetylation of associated histones.

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20
Q

epigenome

A

dna and histones are covered in chemicals called tags
these chemical tags form a second layer known as the epigenome
the epigenome determines the shape of the dna-histone complex
flexible as chemical tags respond to environmental changes

21
Q

epigenetic silencing

A

the epigenome keeps genes that are inactive in a tightly packed arrangement and therefore ensures that they cannot be read (it keeps them switched off)

22
Q

less condensed dna-histone complex

A

where the association of histones with dna is weak, the dna-histone complex is less condensed (loosely packed)
in this condition the dna is accessible by transcription factors, which can initiate production of mRNA, that is, can switch the gene on

23
Q

more condensed dna-histone complex

A

where the association of histones with dna is stronger, the dna-histone complex is more condensed (tightly packed)
in this condition the dna is not accessible by transcription factors, which therefore cannot initiate production of mRNA, that is, the gene is switched off

24
Q

condensation of dna-histone complex

A

inhibits transcription

can be brought about by decreased acetylation of the histones or by methylation of dna

25
Q

decreased acetylation of associated histones

A

decreased acetylation increases the positive charges on histones and therefore increases their attraction to the phosphate groups of dna
the association between dna and histones is stronger and the dna is not accessible to transcription factors
these transcription factors cannot initiate mRNA production from dna
the gene is switched off

26
Q

what is acetylation

A

acetylation is the process whereby an acetyl group is transferred to a molecule
the group donating the acetyl group is acetylcoenzyme A

27
Q

what is deacetylation

A

reverse of acetylation

where an acetyl group is removed from a molecule

28
Q

increased methylation of dna

A

methylation normally inhibits the transcription of of genes in two ways

  • preventing the binding of transcriptional factors to the dna
  • attracting proteins that condense the dna-histone complex (by inducing deacetylation of the histones) making the dna inaccessible to transcription factors
29
Q

what is methylation

A

the addition of a methyl group CH3 to a molecule

the methyl group is added to the cytosine bases of dna

30
Q

epigenetics and disease

A

altering any of the epigenetic processes can cause abnormal activation or silencing of genes
such alterations can have been associated with a number of diseases including cancer

31
Q

treating diseases with epigenetic therapy

A

these treatments use drugs to inhibit certain enzymes involved in either histone acetylation or dna methylation
epigenetic therapy must be specifically targeted on cancer cells

32
Q

the effect of RNA interference on gene expression

A

In eukaryotes and some prokaryotes, translation of the mRNA produced from target genes can be inhibited by RNA interference (RNAi).

33
Q

mechanism involving siRNA sequence

A
  • an enzyme cuts large double-stranded molecules of RNA into smaller sections called small interfering RNA siRNA
  • one of the two siRNA strands combines with an enzyme
  • the siRNA molecule guides the enzyme to a messenger RNA molecules by pairing up its bases with the complementary ones on a section of the mRNA molecule
  • once in position, the enzyme cuts the mRNA into smaller sections
  • the mRNA is no longer capable of being translated into a polypeptide
  • this means that the gene has not been expressed, that is, it has been blocked
34
Q

types of tumour

A

malignant- cancerous

benign- non cancerous

35
Q

benign tumours

A

non cancerous
can grow large in size
cell nucleus has relatively normal appearance
cells are often differentiated (specialised)
cells produce adhesion molecules that make them stick together 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

36
Q

malignant tumours

A

cancerous
can grow to a large size
grow rapidly
cell nucleus is often larger and appears darker than in benign 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 systematic (whole body) effects such as weight loss and fatigue
removal usually involves radiotherapy/or chemotherapy as well as surgery
more frequently reoccur after treatment

37
Q

oncogenes

A

mutations of proto-oncogenes
proto-oncogenes stimulate a cell to divide when growth factors attach to a protein receptor on its cell surface membrane
this then activates genes that cause dna to replicate and the cell to divide
if a proto-oncogene mutates into an oncogene it can become permanently activated (switched on) for two reasons:
-the receptor protein on the cell surface membrane can be 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 stimulated excessive amounts, again stimulating excessive cell division

38
Q

what do oncogenes result in

A

cells that divide too rapidly and out of control, and a tumour or cancer, develops
a few cancers are caused by inherited mutations of proto-oncogenes that cause the oncogene to be activated but most cancer-causing mutations involving oncogenes are acquired, not inherited

39
Q

tumour suppressor genes

A

tsg slow down cell division repair mistakes in dna and tell cells when to die - apoptosis
they therefore have the opposite role from proto-oncogenes
a normal tumour suppressor gene maintains normal rates of cell division and so prevents the formation of tumours
if a tumour suppressor gene becomes mutated it is inactivated
as a result, it stops inhibiting cell division and cells can grow out of control
the mutated cells that are formed are usually structurally and functionally diff from normal cells
while most of these cells die, those that survive can make clones of themselves and form tumours
there are a number of forms of tumour suppressor genes including TP53, BRCA1 and BRCA2

40
Q

abnormal methylation of tumour suppressor genes

A

most common abnormality is hypermethylation (inc methylation)
process by which hypermethylation may lead to cancer:
-hypermethylation occurs in a specific region (promoter region) of tumour suppressor genes
-this leads to the tumour suppressor gene being inactivated
-as a result, transcription of the promoter regions of tumour suppressor genes is inhibited
-the tumour suppressor gene is therefore silenced
-as the tumour suppressor gene normally slows the rate of cell division, its inactivation leads to inc cell division and the formation of a tumour

41
Q

oestrogen concentrations and breast cancer

A

after menopause, a woman’s risk of developing breast cancer increases due to inc oestrogen concs
fat cells of the breasts tend to produce more oestrogens after the menopause. these locally produced oestrogens appear to trigger breast cancer in postmenopausal women
once a tumour has developed, it further increases oestrogen conc which therefore leads to inc development of the tumour
also white blood cells that are drawn to the tumour inc oestrogen production. this leads to even greater development of the tumour

42
Q

genome projects

A

projects to determine the entire dna nucleotide base sequence of a wide range of organisms, including humans, have taken place over the past few decades
the idea has been to map the dna base sequences that make up the genes of the organism and then to map these genes on the individual chromosomes of that organism
in this way a complete map of all genetic material in an organism (the genome) is obtained

43
Q

bioinformatics

A

the science of collecting and analysing complex biological data such as genetic codes
it uses computers to read, store and organise biological data at a much faster rate than previously

44
Q

determining the complete dna base sequence of an organism

A

uses the technique of whole-genome shotgun (WGS) sequencing
this involves researches cutting the dna into many small, easily sequenced sections and then using computer algorithms to align overlapping segments to assemble the entire genome

45
Q

proteome

A

all the proteins produced by the genome
as a protein is only produced when a gene is switched on, and genes are not switched on all the time, a more specific definition is all the proteins produced in a given type of cell (cellular proteome) or organism (complete proteome), at a given time, under specified conditions

46
Q

why is determining the proteome of prokaryotic organisms like bacteria relatively easy?

A
  • the vast majority of prokaryotes have just one, circular piece of dna that is not associated with histones
  • there are none of the non-coding portions of dna which are typical of eukaryotic cells
47
Q

Determining the genome of simpler organisms

A

allows the sequences of the proteins that derive from the genetic code (the proteome) of the organism to be determined. This may have many applications, including the identification of potential antigens for use in vaccine production.

48
Q

Determining the genome of complex organisms

A

the presence of non-coding DNA and of regulatory genes means that knowledge of the genome cannot easily be translated into the proteome.

A Level Biology (20 decks)

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