Home > Subjects > Biology > Level 3 > 3.3 Gene expression > Subject content
- Subject: Biology
- AS: AS90715
- Level: 3
- Credits: 4
- External
Biology 3.3 Describe the role of DNA in relation to gene expression
Subject content
Make sure you have up-to-date course notes. Use them, and if you haven't got them, see your teacher. These are the topics you may be tested on:
The role of DNA in gene expression will include the following topics:
- Structure of DNA, which includes the molecular components and their role in carrying the genetic code. Understand the nucleotide structure of DNA, messenger RNA (mRNA) and transfer RNA (tRNA) and their function.
- Replication of DNA, which includes the processes involved in replication and the role that enzymes have in producing accurate copies.
Check out the DNA Workshop for interactive exercises showing protein synthesis and DNA replication. However, the enzymes required to make the processes happen are not mentioned. For more detailed treatment, go to DNA Replication for excellent animations.
- Control of gene expression.
There are two steps to gene expression:
Transcription, when the information encoded in the DNA is 'copied' to the RNA molecule, and
Translation, when the amino acid sequence is translated into a protein.At level 3 biology, the control of gene expression is limited to factors that operate at the transcription level. The controls that act on a gene expression in eukaryotes are more complex than in prokaryotes. In eukaryotes, transcription and translation take place in different cellular compartments: transcription takes place in the membrane-bounded nucleus, whereas translation takes place outside the nucleus in the cytoplasm. In prokaryotes, the two stages are closely coupled and can happen simultaneously.
- Feedback in prokaryotes. Control of the gene expression is generally achieved by regulatory proteins at the point of initiation of transcription. These proteins can act both positively (inducers) and negatively (repressors).
- Regulation of gene expression in eukaryotes is controlled from many different points, by enhancers and transcription factors.
To understand more about the two major cells of living things – visit prokaryotes and eukaryotes.
You will find more information about the structure and replication of DNA, on the online Molecular Biology Notebook site. Use the menu on the left-hand side to retrieve information on 'Transcription'.
- Protein synthesis, which includes the role of DNA in determining the structure of a protein and how that protein is produced (transcription and translation).
- Determination of phenotype includes:
- allele interactions: dominance, incomplete dominance, co-dominance, multiple alleles, and lethal alleles
- linkage and sex linkage
- gene–gene interactions: epistasis, collaboration, and polygenes
- pleiotropy
Revise dihybrid crosses and sharpen you skills by doing the Bitesize Revision: Genetics and adaptation. Now try these slightly harder problems, which include an epistasis problem: Dihybrid Cross Problem Set.
- gene mutations, for example, Sickle cell disease – a mutation caused by a substitution of a single base; Cystic fibrosis – a mutation caused by a deletion of a triplet
- chromosomal mutations (aneuploidy occurs when there is one or more chromosomes above or below the normal chromosome number, for example: Turner, Down, and Klinefelter syndromes)
- control of metabolic pathways by gene expression.
Read further information about mutations and polyploidy, then try the Test bite: Mutations. These sites have animations showing types of mutations and deals with sickle cell and PKU, both of which you must know about.
