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Biology A2 > 21: Gene Expression > Flashcards

21: Gene Expression Flashcards

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1
Q

Describe the Stimulation of Transcription in Eukaryotes:

A
  • transcriptional factors are found in the cytoplasm of the cell
  • these move into the nucleus
  • each transcriptional factor has a site which binds to the promotor region of DNA (specific base sequence of DNA)
  • binding of transcriptional factor to promotor region of DNA allows the attachment of RNA polymerase to the DNA and transcription is stimulated
  • mRNA produced and subsequently translated into a protein
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2
Q

What is the role of RNA polymerase?
How can transcriptional factors be used to inhibit transcription?

A
  1. attachment of adjacent nucleotides together, via the formation of phosphodiester bonds
  2. could prevent RNA polymerase from binding to DNA, by binding themselves to the DNA
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3
Q

What is Oestrogen?
How does it enter the cytoplasm of the cell?

A
  • lipid-soluble, steroid hormone released into the bloodstream
  • simple diffusion in between the phospholipids
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4
Q

How can Oestrogen initiate Trancription?

A
  • oestrogen enters cytoplasm via simple diffusion
  • this binds to the transcriptional factor in the cytoplasm, causing the transcriptional factor to change shape
  • this causes the inhibitor molecule (on transcriptional factor) to be released, exposing the DNA binding site on the transcriptional factor
  • transcriptional factor now moves into the nucleus and binds to a specific sequence of bases on the promoter region, enabling RNA polymerase to bind and initiate transcription
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5
Q

What is the function of the inhibitor molecule?

A
  • prevents the transcriptional factor from binding to the promotor region of the DNA, so no RNA polymerase can bind when protein synthesis isn’t needed
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6
Q

Describe the effect of RNAi (RNA interference) on Gene Expression:

A
  • double stranded RNAi is coded for by special regulatory genes
  • this moves into the nucleus where it becomes single stranded and associates itself with a nuclease enzyme
  • this now binds to specific mRNA molecules with complementary base pairs via complementary base pairing
  • this enzyme cuts the mRNA into 2
  • translation of mRNA cannot occur so protein synthesis stops
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7
Q

What is RNAi?
When might RNAi be important in a cell?

A
  1. small double stranded sections of RNA, which inhibit gene expression at the translation stage in a process called RNA interference
    • if mRNA concentration needs to be regulated, it can limit the amount of protein translated
    • stops translation of viral RNA in a cell infected by virus
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8
Q

Give 2 applications of RNAi in research:

A
  • prevention of a genetic condition
  • could be used to identify the role of genes in a biological pathway
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9
Q

What are the 2 main features of stem cells?

A
  • undifferentiated but can differentiate into specialised cells
  • they can replace themselves to form more stem cells
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10
Q

What are the 4 main types of Stem Cell and Roles?

A
  1. totipotent cells:
    - occur for a limited time in early mammalian embryos
    - can differentiate to produce any type of body cell, including placental cells
  2. pluripotent cells:
    - found in embryos
    - can differentiate into any type of cell, apart from placental cells
  3. multipotent cells:
    - found in many tissues of mature mammals
    - can differentiate to form a limited number of different cell types e.g stem cells in bone marrow can produce any type of blood cell
  4. unipotent cells:
    - found in mature mammals
    - can only differentiate into one type of cell or tissue
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11
Q

How do Induced Pluripotent Stem Cells (iPS) work?

A
  • these are pluripotent stem cells produced from differentiated adult body cells
  • specific transcriptional factors are used to ‘reprogramme’ the body cells
  • the iPS cells are able to divide to produce new iPS cells or differentiate into any type of body cell
  • these are replacements to the ethically challenging embryotic pluripotent stem cells
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12
Q

Describe the advantages + disadvantages of using stem cell types for production of new cells:
- pluripotent
- multipotent

A

Pluripotent:
- advantage: can differentiate into many different specialised cells
- disadvantage: risk of rejection as they are not the patient own cells + there are ethical issues with using embryos

Multipotent:
- advantage: no organ rejection, as cells are reimplanted from the host
- disadvantage: can only differentiate into a limited number of cell types

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13
Q

What type of Stem Cell are plants?

A
  • mature plants have totipotent cells, which can differentiate into any other cell
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14
Q

Define Epigenetics:
What factors can affect Gene Expression?
Define Epigenome:

A
  • involves heritable changes in gene function, without altering the base sequence of DNA
  • environmental factors such as:
    1. diet
    2. stress
    3. toxins
  • comprises of all the chemical tags which have been added to a persons genome
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15
Q

Describe the increased Acetylation of Histones:

A
  • acetyl groups bind to histone proteins
  • this causes the DNA to be less tightly wrapped around histones, which causes chromatin to be less condensed
  • this increases accessibility of promotor region
  • transcriptional factors can now bind to promotor region and initiate transcription
  • genes are now switched on
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16
Q

Why does the increased Acetylation of Histones lead to less tightly wrapped DNA?

A
  • DNA is negatively charged (due to phosphate group), so is attracted to positive charged histones
  • Addition of acetyl group decreases the positive charge, so less attraction
17
Q

Describe the Increased Methylation of DNA:

A
  • methyl group are added to cytosine bases of DNA
  • this leads to decreased acetylation of histones
  • DNA wraps more tightly around histones, and increased condensation of chromatin occurs
  • this then leads to promotor regions becoming inaccessible to transcriptional factors
  • transcription is inhibited
  • gene is switched off
18
Q

What are non-cancerous tumours called?
How does this occur?

A
  • benign tumour:
    • a benign tumour is a mass of cells that has not spread into neighbouring tissues
  • the location of the tumour is restricted to only one part of the body
  • not cancerous as they do not invade surrounding tissues
19
Q

What are cancerous tumours called?
How do these tumours occur?

A
  • malignant tumours
  • tumours are uncontrollably dividing cell groups that may spread/metastasise, to other parts of the body
20
Q

How does Chemotherapy work?
How does Radiation-Therapy work?

A
  • drugs killing fast-growing cancer cells
  • uses ionising radiation to damage the DNA of the cancer tissue to kill the abnormal cells
21
Q

Describe the normal role within a cell of:
1. Proto-Oncogene
2. Tumour Suppressor Gene

A
  1. stimulates cell division
    • inhibits cell division
    • repairs faulty DNA
    • instructs cell death of faulty cells (apoptosis)
22
Q

What happens to the Proto-Oncogene and the Tumour Suppressor Gene when mutated?

A

Proto-Oncogene:
- becomes an oncogene
- gene is permanently active
- cells divide continuously by mitosis

Tumour Suppressor Gene:
- tumour suppressor gene is inactivated
- cells divide continuously by mitosis

23
Q

______ DNA ____________ can lead to cancer

A

Abnormal DNA methylation can lead to cancer

24
Q

Describe how Hypermethylation (too much) of Tumour Suppressor Gene could lead to cancer:

A
  • increased methylation
  • methyl groups are added to cytosine bases in DNA
  • decreased acetylation of histones
  • transcription of gene is inhibited
  • no translation producing any protein
  • protein no longer inhibits cell division
  • cell divides rapidly by mitosis
25
Q

Describe how Hypomethylation (too little) of Proto-Oncogene could lead to cancer:

A
  • permanent activation of the gene (becomes an ocogene)
  • decreased methylation of cytosine bases in DNA
  • increased acetylation of histones proteins
  • transcriptional factors can bind to promotor regions initiating transcription
  • translation produces protein continuously
  • protein stimulated for cell division by mitosis top quick
26
Q

Describe how increased concentrations of Oestrogen could lead to Breast Cancer:

A
  • oestrogen enters cytoplasm via simple diffusion
  • oestrogen binds to transcriptional factor causing an alteration of shape
  • this causes the inhibitor molecule to be removed, exposing the DNA binding site of transcriptional factor
  • so more transcriptional factors can bind to promotor region of DNA
  • more transcription/translation of proto-oncogene
  • so the proto-oncogene becomes a oncogene, and is permanently active causing the cancerous cells to constantly divide
27
Q

Define:
- genome
- proteome

A
  1. complete set of genes in a cell/organism
  2. full range of proteins produced by a given cell

Biology A2 (16 decks)

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