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12 Cards in this Set
- Front
- Back
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Describe the first step of DNA replication: |
- Hydrogen bonds between base pairs are broken by the action of the enzyme DNA helicase; the single strands move apart. This occurs at many points along the length of the chromosome, creating many replication forks.
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Describe the second step of DNA replication: |
- Each of the strands acts as a template for new DNA strand. Short RNA primers attach to the single DNA strands and initiate replication. - Individual nucleotides are added at the 3' end of the DNA strand according to base pairing rule. This process is catalysed by an enzyme, DNA polymerase. |
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Describe the third step of DNA replication: |
- One DNA strand, the leading strand, forms continuously in the direction of replication. DNA fragments formed on the lagging strand are joined by the enzyme DNA ligase. |
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Describe the fourth step of DNA replication: |
Each of the new double-helix molecules is an exact copy of the original DNA. - The process is semi-conservative; that is, each of the new double-stranded molecules contain one of the original DNA strands and one DNA strand. |
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What, in the DNA determines what proteins are produced: |
The sequences of bases in a gene determines the amino acids that are used in building the protein molecule. |
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How is a genetic code 'written'? |
It is written in a sequence of three bases (called a DNA triplet). A DNA triplet containing AGC will code for one triplet, while a DNA triplet containing TTA will code for another. |
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How many triplets exist? |
64 triplets exist. |
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Can more than one triplet code for a particular amino acid? |
Yes. Eg: CAA and CAT both code for valine. It can therefore be said that the code is redundant. |
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What is mRNA? |
Messenger RNA is a single-stranded nucleic acid that is transcribed from DNA. It carries instructions for protein manufacture from the nucleus to the ribosomes. |
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What is transcription? |
The production of a molecule of pre-mRNA from a DNA template. |
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Describe the process of transcription: |
The process of transcription begins when a section of DNA unwinds and the bases separate. This exposes two single strands of DNA with unpaired bases. One of these strands acts as a template for the for the formation of an mRNA molecule (it is transcribed). Each transcription process contains the instructions for the formation of a protein. Each 3-base sequence in an mRNA molecule will code for one amino acid. |
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What is a codon? |
A three-base triplet in mRNA that codes for a particular amino acid. |
