DNA and genetics
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- Created by: erinmcgarry3
- Created on: 09-01-19 19:44
what were the two main ideas of how DNA replicated called?
conservative and semi-conservative replication
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why do we need DNA to replicate?
we can pass on genetic information from one cell to another or generation to another
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who produced the double helix model?
watson and crick
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what does the conservative model consist of?
the original double helix remained intact and instructed the formation of a new, identical double helix, made up of entirely new material
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what does the semi-conservative model consist of?
DNA 'unzips' along hydrogen bonds and new nucleotides aligned along each strand. each new double helix contained one original strand and one new strand.
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which view did watson and crick support?
semi-conservative view
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who carried out evidence to support either view? where did they do this and in what decade?
messelson and stahl in california in the late 1950s
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what did they do?
they grew several generations of e.coli in medium where source of nitrogen was isotope ¹⁵N ('heavy' nitrogen), moved bacteria to medium containing normal nitrogen isotope (¹⁴N) and measured density as they reproduced
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what were their results and which view did it support?
all the DNA had the same density (halfway between that of ¹⁴N and ¹⁵N) so DNA must replicate semi-conservatively
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explain, in detail, how DNA replicates itself. (1)
two strands of DNA 'unzip' along h bonds, catalysed by DNA helicase, strands act as templates for new DNA strands, exposed bases attract free DNA nucleotides and new h bonds formed between matching base pairs
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explain, in detail, how DNA replicates itself. (2)
DNA polymerase lines up and catalyses linking of nucleotides along template strand. DNA ligase catalyses formation of phosphodiester bonds between the two strands of DNA. new DNA coils.
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why does DNA automatically coil into a double helix?
happens when weak h bonds form within the structure
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what is the genetic code?
rules used for translation on ribosomes
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what does it consist of?
64 codons (triplet of nucleotide bases)
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what is a gene?
a sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide that affect a characteristic in the phenotype of an organism
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when and what is considered the cornerstone of the genetic code?
early 1960s and the triplet code
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what is a codon?
sequence of three bases on the DNA or RNA
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why was work done on the codons of mRNA?
DNA is too large to solve, mRNA is complementary strand to DNA
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what is a complementary strand?
a reverse image of the original base sequence
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what organism is used to solve the genetic code?
e. coli gut bacteria
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what are the two types of DNA?
codes for protein and doesn't code for protein
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what percentage of human DNA is non-coding?
98%
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what does non-coding DNA do?
involved in regulating the protein-coding sequences, suggests they are useful
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what does coding DNA do?
some codons code for particular amino acid, others code for beginning or ending of particular amino acid sequence
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what can the genetic code be described as? (3)
triplet code, non-overlapping code, degenerate code
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what does non-overlapping mean?
two codons makes two amino acids, not four, base used once. eg. UUUAGC makes two rather than four
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what would be an advantage of an overlapping code?
economical; short lengths of DNA could carry instructions for many different proteins
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what would be a disadvantage of an overlapping code?
higher risk of mutation affecting entire phenotype (will affect one amino acid rather than two)
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what does degenerate (redundant) mean?
amino acid represented by more than one codon
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what would be an advantage of a degenerate code?
if a mutation occurs, won't completely affect organism
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which two amino acids are the exception and how?
methionine and tryptophan because they only have one codon
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when and where did the first breakthrough for the genetic code happen and because of who?
in 1961; Nirenburg and Matthaei in US
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what did they do?
prepared artificial mRNA where all bases were uracil, added ingredients needed for protein synthesis (ribosomes, etc.)
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what were their results?
they saw a single type of amino acid, phenylalanine, for UUU so for DNA it would be that for AAA
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what did they then show?
that CCC codes for proline and AAA for lysine, the opposite for DNA
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Other cards in this set
Card 2
Front
why do we need DNA to replicate?
Back
we can pass on genetic information from one cell to another or generation to another
Card 3
Front
who produced the double helix model?
Back
Card 4
Front
what does the conservative model consist of?
Back
Card 5
Front
what does the semi-conservative model consist of?
Back
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