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23 Cards in this Set
- Front
- Back
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Define allele |
One of a no. of alternate forms of a gene |
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Define gene |
Section of DNA on a chromosome coding for one or more polypeptides of functional RNA |
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How are mitochondria and chloroplasts similar to prokaryotes? |
Circular DNA 70S ribosomes |
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How is Prokaryotal DNA diff. to Eukaryotal? |
Prokaryotal; circular, shorter, not assocated w/ prot.s, NO INTRONS |
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How does prokaryotal DNA condense? |
Coils, then supercoils |
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Features of genetic code |
Degenerate Non-overlapping (each triplet only read once) Universal (each triplet almost always codes for the same amino acid in different organisms) |
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Why is the genetic code degenerate? |
Most amino acids are coded for by more than one triplet |
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What is significant about the start and end of every DNA sequence which codes for a polypeptide? |
Always the same triplet at start Codes for methionine If methionine is not in the final polypep. then it is later removed Stop codes Do not code for any amino acid 3 triplets at end mark end of polypep. chain |
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How many possible triplets are there from 4 bases? |
4^3=64 Only 20 amino acids Therefore code is degenerate |
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Transcription |
RNA polymerase attaches to DNA double helix at start of a gene; it moves along the DNA, assembling the RNA molecule by doing the following: Goes from 5' to 3' H-bonds break - HELICASE - exposing some of bases Double helix uncoils at that point Free RNA nucleotides are attracted to the exposed bases on the template strand b/c of base pairing rule RNA polymerase forms phosphodiester bonds H-bonds reform once RNA polymerase has passed by; coils back into double helix RNA polymerase detaches from the DNA when it reaches a stop code (3 stop triplets), and stops making RNA This is pre-mRNA In eukaryotes, splicing occurs (spliceosomes), removing introns; the remaining mRNA leaves through the nuclear pores |
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Translation |
mRNA attaches to a ribosome tRNA attaches to an amino acid at the amino acid binding site; ATP provides the E for this bond to form tRNA attaches to the mRNA; its anticodon is complementary to the first codon of mRNA. Specific base pairing. Therefore the mRNA codon specifies the amino acid First codon is always AUG; matches with UAC. Therefore first amino acid is always methionine A second tRNA molecule binds to the second mRNA codon; the two amino acids from adjacent tRNAs form peptide bonds First tRNA molecule moves away, leaving behind its amino acid Process continues; as one comes, the other tRNA moves away leaving behind its amino acid Process stops when there is a stop code on the mRNA Polypep. chain moves away |
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Structure of 5' end of mRNA |
Modified guanine base; 'cap' |
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Structure of 3' end of mRNA |
Between 50 & 250 adenine bases; 'poly-A tail' |
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Structure of ribosome |
Small subunit; binding site for mRNA Large subunit; binding site for tRNA |
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DNA Coding Strand |
The DNA strand complementary to the template strand; this is the sequence that is the same (except the change in base from T to U) as the mRNA, and is therefore the strand which the protein is based on. |
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Define proteome |
The entire set of proteins able to be expressed by a cell |
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Define genome |
An organism's complete set of DNA In humans, every cell w/ a nucleus contains the genome All info needed to build and maintain that organism |
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Types of mutation |
Substitution; doesn't always change order of amino acids in a protein - degenerate Deletion Addition/insertion Both cause a shift in all base triplets after; frame shift mutations |
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What causes mutations |
Errors in DNA replication |
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Define mutanigenic agents |
Things which cause an increase in the rate of mutations |
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Examples of mutanigenic agents |
UV radiation Ionising radiation |
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How do mutanigenic agents work? |
Acting as a base Base analogs can sub. for a base during DNA repl. and change base sequence in new DNA Altering bases e.g. alkylating agents can add alkyl group to guanine; makes it bind with thymine instead of cytosine Change the structure of DNA |
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Homologous chromosomes |
Pair of chromosomes One paternal, one maternal Same gene loci Therefore determine same features Capable of pairing during meiosis Not necessarily identical |
