Nucleic Acids: The Molecules of Life. DNA and RNA Both are polymers. They are made up of monomers...
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Transcript of Nucleic Acids: The Molecules of Life. DNA and RNA Both are polymers. They are made up of monomers...
![Page 1: Nucleic Acids: The Molecules of Life. DNA and RNA Both are polymers. They are made up of monomers called nucleotides.](https://reader038.fdocuments.in/reader038/viewer/2022110323/56649d835503460f94a69d99/html5/thumbnails/1.jpg)
Nucleic Acids:
The Molecules of Life
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DNA and RNA
Both are polymers.
They are made up of monomers called nucleotides
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phosphate sugar base
CH2
OC
C C
C
O
O
O
OP
-
-
N1’
2’3’
4’
5’
OH OH
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• Nucleotides have three parts to them: • a phosphate group • a pentose sugar• a nitrogenous base.
![Page 5: Nucleic Acids: The Molecules of Life. DNA and RNA Both are polymers. They are made up of monomers called nucleotides.](https://reader038.fdocuments.in/reader038/viewer/2022110323/56649d835503460f94a69d99/html5/thumbnails/5.jpg)
DNA: deoxyribonucleic acid
RNA: ribonucleic acid
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Phosphodiester bonding…
• Joins nucleotides together• Condensation reaction• Eliminates H2O molecule
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The Bases
• Pyramidines: thyminecytosine
• Purines: adenineguanine
RNA has URACIL instead of thymine
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Base pairing…
• Complementary base pairing
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http://uk.youtube.com/watch?v=qy8dk5iS1f0
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Watson and Crick Model (and Franklin…)
DNA
X-ray crystallograph
y
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DNA REPLICATIONWhen cells divide, you need to have 2 copies of the DNA in the cell
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DNA Replication
• Most important feature of DNA is its ability to replicate itself, (almost) exactly
• The double helix is ‘unzipped’ during replication
• New nucleotides are aligned along the DNA strands (built by DNA polymerase)
• The new helix contains one original strand and one new strand
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1
2
3
4
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Semi - conservative replication – Meselson & Stahl
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READING THE CODEDNA carries the information to allow protein synthesis
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How is DNA organised?
• You have roughly 1m of DNA in a cell!• It is stored in sections: chromosomes• Each chromosome is coiled up around proteins
(histones) so it fits in a cell• A section of a chromosome that codes for a
protein is called a gene• Different versions of genes (allelles) arise from
mutations of the DNA code
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DNA – genetic code
• Strings of base pairs make up a code (GENE)
• The 4 base pairs are arranged in triplets called CODONS
• Codons each encode a unique AMINO ACID
• Codons are copied (transcribed) from the DNA molecule into a molecule of mRNA
• The mRNA containing the codons is ‘translated’ into amino acids at the ribosomes (outside the nucleus)
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Triplet code – genetic
translation table
Triplet codes are
degenerate
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Protein synthesis
• The central dogma:
DNA is transcribed to mRNA which is translated into proteins
http://www.youtube.com/watch?v=41_Ne5mS2ls
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RNA
Uses uracil instead of thymidine
It travels out of the nucleus to the cytoplasm where it is translated into amino acids by the ribosomes
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Mutation….
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Genetic mutations
• Single codons or base pairs can be mis-read or mismatched during replication/transcription
• These changes are known as MUTATIONS
• These may have no effect OR can alter the structure/function of proteins
• Mutations can be passed to offspring and can result in genetic diseases
• Chances of mutation happening in DNA replication is 2-30x10-7
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Effect of mutation on whole organisms
• A source of variation
• Occasionally results in new protein/function
• Could give reproductive advantage
• Basis of evolution by natural selection
• Most likely to occur during replication
• Mutagen increase rate of mutagenesis