Topic 8.1 and 8.2 Flashcards
When do gene mutations arise?
During DNA replication. They occur spontaneously.
What are mutagenic agents?
Name at least 3 examples:
An agent which makes mutations more likely to occur.
E.g.
- High energy radiation
- Ionising radiation (alpha, beta)
- Chemicals such as benzene or mustard gas
What do we mean when we say a gene has been expressed?
The protein it codes for has been produced.
The gene has been transcribed and translated.
At which points during proteinsynthesis might there be an opportunity to regulate gene expression?
- Transcription
- Splicing
- Translation
What is a promoter region?
Marks the beginning of a gene - where a transcription factor can bind to.
What is a terminator region?
Marks the end of a gene.
What is a transcription factor?
- A transcription factor binds to a gene
- At a specific DNA base sequence in the promoter region.
- Stimulates RNA polymerase to attach and transcribe the gene.
Or it can prevent transcription by blocking that point so RNA polymerase can not bind.
How would a transcription factor increase the production of a protein?
- Transcription factor moves from the cytoplasm of a cell into the nucleus.
- It binds to the promoter region of the gene.
- This will cause RNA polymerase to attach and stimulate transcription to take place.
- Therefore, more of the protein will be produced.
What type of molecule is oestrogen?
It’s a steroid hormone.
Describe how oestrogen affects gene transcription:
- Oestrogen binds to the oestrogen receptor (which is found in the cytoplasm).
- This causes the tertiary structure of the receptor to change (a conformational change).
- Inhibitor molecule will be released from the receptor, exposing the DNA binding site.
- Oestrogen receptor leaves the cytoplasm and enters the nucleus via the nuclear pore
- Binds to the specific base sequence in the promotor region of a gene.
- This stimulates RNA polymerase to attach and for transcription to take place.
What is the function of RNAi?
RNA molecules (such as siRNA or mircoRNA) inhibit gene expression by ‘neutralising’ specific mRNA molecules so that translation cannot take place.
They bind to complementary mRNA sequences (of a specific gene) either preventing the mRNA from attaching to the ribosome or break up the mRNA.
What is the structure of RNAi?
Short RNA molecules that are transcribed from a cell’s DNA.
How is a molecule of RISC formed?
A single strand of RNAi can bind to proteins in the cytoplasm to form a RISC complex.
Describe how RNAi functions:
- Double stranded RNA is produced
- Leaves the nucleus
- One strand of RNAi is bound to RISC (a complex with proteins, including RNA hydrolase).
- The RNAi guides the enzyme to mRNA
that has a complementary sequence of
bases - The RNAi binds to the mRNA by
complementary base pairing. - Either the enzyme RNA hydrolase allows the hydrolysis of the mRNA strand, permanent action.
OR the mRNA is blocked from binding to a ribosome.
Either way, translation is prevented.
What is epigenetics?
The study of heritable changes in gene function that do not involve changes to the base sequence.
What is DNA methylation?
The addition of methyl groups to DNA bases, usually cytosine.
Describe and explain the effect of increased DNA methylation on gene expression:
- Increased methylation of DNA in the promoter region of a gene will prevent transcription factors and RNA polymerase from binding
- Transcription of the gene will be inhibited and the gene will be ‘silenced’
What are histones?
The proteins that DNA is wrapped around.
What is histone acetylation?
The addition of acetyl groups to histone proteins.
. Describe and explain the effect of histone acetylation on gene expression
- Histone acetylation causes the DNA to be less condensed.
- Which can reveal promoter regions of the gene.
- Leads to increased binding of transcription factors and RNA polymerase to the promoter regions.
- Leading to increased transcription of the gene.
What are the main characteristics of a benign tumour?
A mass of dividing cells which do not break away and invade neighbouring tissue, does not spread/metastasize.
What are the main characteristics of a malignant tumour?
A mass of cells which divide uncontrollably and can metastasize, invading other tissues.
What can an oncogene do?
Codes for a protein which stimulates cell division to occur.
What is the consequence of a mutation occurring to an oncogene?
- Change in base sequence of DNA
- Changes the primary structure of a protein (amino acid sequence)
- Change in tertiary structure of the protein.
- This results in uncontrollable cell division.
