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A LEVEL BIOLOGY > Gene expression > Flashcards

Gene expression Flashcards

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1
Q

Substitution of bases

A

Depending on which new base is substituted of bases:

  • formation of one of tree stop codons that mark the end of a polypeptide chain, the production of a polypeptide would be be stopped and the final protein would be significantly different and the production can’t perform its function
  • the formation of a codon for a different amino acid meaning the structure of the polypeptide produced would differ, the protein may differ in shape and not function properly e.g for an enzyme the active site may no longer fit the substrate
  • formation of a different codon but one that produces a codon for the the same amino acid, this is because the genetic code is dengenerate. The mutation therefore has no effect on the polypeptide produced
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2
Q

Deletion of bases

A
  • minor through the loss of a single base might seem, the impact on the phenotype can be enormous
  • the one deleted base creates a frame shift because the reading frame that contains each 3 letters of the code has been shifted to the left
  • most triplets will be different as will the amino acid they code for
  • the polypeptides will be different and lead to the production of a non-functional protein that could possibly alter the phenotype
  • one deletion could alter every triplet in the sequence
  • a deleted base at the end is more likely to have a smaller impact
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3
Q

Other types of gene mutation

A
  • Addition of bases: an extra base is added which usually has a similar effect to a base deletion in that there is a frame shift and sequence of triplets become altered
  • Duplication of bases: one or more bases are repeated this produces a frame shift to the right
  • Inversion of bases: group of bases become separated from the DNA sequence and rejoin at the same position but in the inverse order. The base sequence is reversed and this effects the amino acid
  • Translocation of bases: a group of bases become separated from the DNA sequence on one chromosome and become inserted into the DNA sequence of a different chromosome. Translocation lead to a abnormal phenotype
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4
Q

The effect of oestrogen on gene transcription

A

principles involved in controlling the expression of a gene by controlling transcription:

  • for transcription to begin the gene is switched on by transcription factors that move from the cytoplasm into the nucleus.
  • Each transcriptional factor has a site that binds to a specific base sequence of the DNA in the nucleus
  • mRNA is produced and the info it carries is then translated into a polypeptide
  • When a gene is not being expressed, the site on the transcriptional factor that binds to the 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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5
Q

Hormones like oestrogen can switch on a gene and thus start transcription by combining with a receptor site on the transcriptional factor. This activates the DNA binding site by causing it to change shape. The process is:

A
  • oestrogen is a lipid-soluble molecule and therefore diffuses easily through the phospholipid portion of cell-surface membranes
  • once inside the cytoplasm of a cell, oestrogen binds with a site on a receptor molecule of the transcriptional factor, the shape of the site and shape of oestrogen molecule complement one another
  • by binding with the site, the oestrogen changes the shape of the DNA binding site on the transcriptional factor, which can now bind to DNA
  • 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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6
Q

All cells contain genes but

A

only certain genes are expressed (switched on) in any one cell at any one time
- some genes are permanently expressed in all cells. For example the genes that code for essential chemicals, such as the enzymes involved in respiration are expressed in all cells

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7
Q

What is totipotency?

A

An organism develops from a single fertilised egg

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8
Q

What are totipotent cells?

A

Cells such as fertilised eggs which can mature into any body cell
- early cells derived from the fertilised eggs are also totipotent

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9
Q

Pluripotent stem cells

A

found in embryos and can differentiate into almost any type of cell. Examples of pluripotent stem cells are embryonic stem cells and fetal stem cells

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10
Q

Multipotent stem cells

A

found in adults and can differentiate into a limited number of specialised cells. They usually develop into cells of a particular type. Stem Cells in the bone marrow can produce any type of blood cell
- Examples of multipotent cells are adult stem cells and umbilical cord blood stem cells

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11
Q

Unipotent stem cells

A

can only differentiate into a single type of cell. They are usually derived from multipotent stem cells and are made in adult tissue

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12
Q

What are stem cells?

A

cells that retain the ability to differentiate into other cells
OR
Stem cells are undifferentiated dividing cells that cells that occur in adult animal tissues and need to be replaced
- they have the ability to divide to form an identical copy of themselves

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13
Q

Example of a cell that can’t develop into any other cell

A

Xylem Vessels:
- they transport water in plants, and red blood cells which carry oxygen. The red blood cells are so specialised that they lose their nuclei once they mature. The nucleus contains the genes then these cells cannot develop into other cells

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14
Q

Stem cells originate from various sources in mammals:

A
  • Embryonic stem cells: come from embryos in the early stages of development. They can differentiate into any type of cell in the initial stages of development
  • Umbilical cord blood stem cells are derived from umbilical cord blood and are similar to adult stem cells
  • Placental stem cells: are found in the placenta and develop into specific types of cells
  • Adult stem cells: they’re found in the body tissues of the fetus through to the adult. They’re specific to a particular organ or tissue within which they produce the cells to maintain and repair tissues throughout an organism
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15
Q

What are epigenetics?

A

Environmental factors can cause heritable changes in gene function without changing the base sequence of DNA
Environmental factors like:
- diet
- stress
- toxins
These factors may alter the genetic inheritance of an organism’s offspring

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16
Q

Epigenome

A

DNA and histones are covered in chemicals called tags. these chemical tags form a second layer known

17
Q

What is a epigenome?

A

it determined the shape of DNA- histone complex. For example it keeps genes that are inactive in a tightly packed arrangement and therefore ensures that they cannot be read. This is known as epigentic silencing, it unwraps active genes so DNA is exposed and can be transcribed (switches them on)

18
Q

Induced pluripotent stem cells

A
  • iPS are a type of pluripotent cell that is produced from unipotent stem cells
  • unipotent cell may be any cell in the body and these cells are genetically modified in a lab to make them acquire the required characteristics of embryonic and they do this by inducing genes and transcriptional factors within the cell to express themselves
  • the fact that these genes are capable of being reactivated shows that adult cells retain the same genetic info that was present in the embryo
  • iPS cells are capable of self-renewal so they can potentially divide indefinitely to provide a limitless supply
  • iPS could replace embroyonic stem cells in medical research and treatment and so overcome many ethical issues surrounding the use of embryos
19
Q

Pluripotent cells in treating human disorders

A
  • cells can be used to regrow tissues that have been damaged (e.g. skin grafts for serious burns
20
Q

Difference between DNA code and epigenome

A

DNA code is fixed and epigenome is flexible

  • this is because the chemical tags respond to environmental changes
  • factors like diet and stress can cause the chemical tags to adjust the wrapping and unwrapping of the DNA and so switch genes on and off
21
Q

Epigenome of a cell

A
  • acts like a cellular memory because of all the signals its received in its lifetime
  • in its early stages, signals come from within the fetus and nutrition comes from the mother but when its older, hormones influence the epigenome. it can either activate or inhibit specific genes
22
Q

message passes to a specific protein which can be attached to a specific sequence of bases on the DNA. once attached the protein has two possible effects. It can change

A
  • acetylation of histones leading to activation or inhibition a gene
  • methylation of DNA by attracting enzymes that can add or remove methyl groups
23
Q

DNA histone complex (chromatin)

A
  • DNA histone complex is less condensed (loosely packed) in this condition DNA is accessible by transcription factors which cannot initiate production of mRNA, that is, the gene is switched off
  • when histone association is stronger, the complex is more associated
  • condensation of the complex inhibits transcription and can be brought about by decreased acetylation of the histones or methylation of DNA
24
Q

decreased acetylation of associated histones

A
  • acetylation is the process whereby an acetyl group is transferred to a molecule and in this case the group donating is acetylcoenzyme A
  • deacetylation is reverse reaction where an acetyl group is removed from a molecule
  • decreased acetylation increases the positive charges on histones and therefore increases their attraction to the phosphate group
  • 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. in the other words, the gene is switched off
25
Q

Increased methylation of DNA

A

methylation normally inhibits the transcription of genes in two ways:

  • preventing the binding of transcriptional factors to the DNA
  • attracting proteins that condense the DNA histone complex making the DNA inaccessible to transcription factors
26
Q

Epigenetics and inheritence

A

in humans when a mother has a condition known as gestational diabetes, the fetus is exposed to high concentrations of glucose and this causes epigentic changes in the daughters DNA, increasing the likelyhood that she will develop gestational diabetes herself

27
Q

epigenetics and disease

A

epigenetic changes are part of normal development but can be responsible for certain disease.

  • altering epigenetic process can cause abnormal activation or silencing of genes and could cause cancer
  • promoter regions have no methylation in normal cells but in cancer cells, these regions become highly methylated causing genes that are active to be switched off— this happens in the early stages of cancer
28
Q

Treating diseases with epigenetic therapy

A
  • epigentic treatments are used to treat epigenetic changes
  • these treatments use drugs to inhibit certain enzymes involved in either histone acetylation or DNA methylation
  • e.g drugs inhibit enzymes that cause DNA methylation can reactivate genes that have been silenced
29
Q

The effect of RNA interference on gene expression

A

in eukaryotes and some prokaryotes the translation of mRNA produced by a gen e can be translated into a polypeptide.
- One type of small RNA molecule that may be involved is small interfering RNA molecule that may be involves is mall interfering RNA (siRNA)

30
Q

Mechanism involving small double- stranded sections of siRNA operates as follows

A
  • An enzyme cuts large double-stranded molecules of RNA into smaller sections called small interfering RNA
  • one of the two two siRNA strands combines with an enzyme
  • The siRNA molecules guides the enzymes to a messenger RNA molecule by pairing up its bases with the complementary ones on a section of the mRNA
  • 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
31
Q

Types of tumors

A
  • cancerous are called malignant

- non cancerous are called benign

A LEVEL BIOLOGY (7 decks)

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