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34 Cards in this Set
- Front
- Back
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What is the name of the RNA that transfers DNA from the nucleus to the cytoplasm?
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Messenger (m)RNA
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What is a codon?
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The sequence of three bases (triplet) on mRNA that codes for a single amino acid
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'The sequence of nucleotide bases on mRNA, which codes for amino acids' is known as...
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The genetic code
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The genetic code is said to be degenerate - what does this mean?
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Most amino acids have more than one codon
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What is a stop codon?
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Codons that do NOT code from an amino acids - mark the end of a polypeptide chain
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'A polymer made up of repeating mononucleotide sub units' is the definition of...
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mRNA
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What are the two types of RNA?
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mRNA and tRNA
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In RNA, thymine is replaced with...
And the deoxyribose sugar is replaced with a... |
...uracil
...ribose sugar |
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What is the point of one end of the tRNA chain extending beyond the other?
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So the amino acid can attach
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What is the name for the sequence of three organic bases on the base of tRNA?
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anticodon - situated on the anticodon loop
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Briefly outline transcription
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When a complementary section of DNA sequence is made in the form of pre-mRNA
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Briefly outline translation
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When mRNA and complementary tRNA attach and the amino acids they carry are linked to form a polypeptide
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What is a 'template strand' of DNA?
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The strand that RNA polymerase moves along during transcription
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What does RNA polymerase do?
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Causes nucleotides to join with the TEMPLATE STRAND (nucleotides come from a pool present in the nucleus)
REMEMBER: uracil, NOT thymine, binds to adenine |
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During transcription, how many base pairs are exposed?
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Only twelve - so well protected
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How does transcription stop?
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RNA polymerase reaches a sequence on the DNA that is a 'stop' triplet - the strand is then detached - production of pre-mRNA is complete
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What is an intron? What is an exon?
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An intron is a section of DNA that does not code for a protein, while an exon is a section which does
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What happens during the process of splicing?
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Non-functional introns are removed and the functional exons are joined together (NB this happens in EUKARYOTIC CELLS)
The exons can be oriented in many different ways (Hence a single gene can code for dozens of different proteins) |
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Hwo does mRNA leave the nucleus?
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Via a nuclear pore - it is too large to diffuse out of the nucleus
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Each amino acid has its own tRNA molecule, with its own anticodon of bases
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.
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Outline the process of synthesising a polypeptide (7)
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Ribosome attaches to starting codon at one end of mRNA
tRNA moves to ribosome and pairs up with sequence on mRNA Another tRNA binds with the next codon on mRNA The ribosome moves along the mRNA and by means of an enzyme and ATP , the two amino acids are joined by a peptide bond The ribosome moves on to the third codon and the first tRNA is released and collects another amino acid The synthesis continues until a ribosome reaches a stop codon |
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Up to 50 ribosomes can pass immediately behind the first, so that many identical polypeptides can be assembled simultaneously
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.
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What is a 'substitution'?
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A type of gene mutation in which a nucleotide in a DNA molecule is replaced by another that has a different base (nonsense, mis-sense and silent)
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What is a nonsense mutation?
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When a base change results in formation of one of the three stop codons - protein cannot perform normal function
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What is a mis-sense mutation?
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When the base change results in a different amino acid being coded for - significance depends on the role of the amino acid
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What is a silent mutation?
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This occurs when a substituted base, that is different, has no effect and codes for the same amino acid as before (due to to he degenerate code)
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What is a deletion mutation?
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When a nucleotide is lost from the normal DNA sequence
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During deletion mutation, a 'frame shift' is said to occur - what is this?
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The reading frame that contains each three letters of the code has been shifted to the left by one letter. The gene is now read in the wrong three-base groups and the genetic message is altered. A deletion at the start could alter every triplet in the sequence! A deletion ta the end is likely to have a smaller impact
e.g. THE RED HEN - if T is deleted, it is read - HER EDH EN (doesn't make sense!) |
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If a mutation rate is increased by outside factors, it is known as a
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mutagenic agent, or mutagen
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What are two factors that can act as mutagens?
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High energy radiation
Chemicals that can alter the DNA structure/affect transcription |
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How is cell division controlled?
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Using proto-oncogenes (stimulate cell division) and tumour suppressor genes (slow cell division)
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How are genes 'switched on' in a cell?
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Growth factors attach to receptor proteins on the cell-surface membrane, and via RELAY PROTEINS in the cytoplasm, switch on the genes necessary for DNA replication
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How can oncogenes affect cell division?
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The receptor protein on the cell-surface membrane can be permanently activated - leading to cell division being switched on even in the absence of growth factors
The oncogene may code for a growth factor that is then produced in excessive amounts - stimulating excessive cell division |
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What is the problem with rapid cell division?
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A tumour develops which leads to cancer
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