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Biology: Topic 3 > Gene Expression > Flashcards

Flashcards in Gene Expression Deck (14):

Define the term 'cell's genome'.

The cell's entire set of DNA


How do stem cells become specialised?

1. All stem cells contain the same genes but not all are expressed as not all genes are active.
2. mRNA from active genes is transcribed
3. mRNA from active genes is then translated into proteins
4. The proteins modify the cell-determine the cell structure and control cell processes
5. Changes to cell produced by these proteins cause the cell to become specialised
6. These changes are difficult to reverse, so once a cell becomes specialised it stays that way.


How is gene expression controlled?

By altering the rate of transcription of the genes.


How is the rate of transcription controlled?

Transcription factors.


What are transcription factors?

Proteins that bind to DNA and activate or deactivate genes by increasing or decreasing the rate of transcription.


What are activators?

Proteins that increase the rate of transcription as the help RNA polymerase to bind to the DNA and begin transcription.


What are repressors?

Proteins that decrease the rate of transcription by preventing RNA polymerase binding to the DNA and stopping transcription.


What happens to transcription factors in eukaryotic cells?

They bind to specific DNA sites near the start of their target genes.


What happens to transcription factors in prokaryotic cells?

They bind to operons at their target genes.


What is a target gene?

The gene that they control the expression of.


What is an operon?

A section of DNA, in a prokaryotic cell, that contains a cluster of structural genes, control elements and sometimes a regulatory gene.


Describe the function of structural genes in a prokaryotic cell.

They code for useful proteins, such as enzymes, to be synthesised.


Describe the function of control elements in a prokaryotic cell.

- 2 types: a promoter or an operator.
1. Promoter: part of a DNA sequence located before the structural genes that RNA polymerase binds to.
2. Operator: part of a DNA sequence that transcription factors bind to.


Describe the function of the regulatory gene in some prokaryotic cells.

It codes for an activator or a repressor.