OCR AS Biology- DNA and RNA

Complete set of revision notes for OCR As Biology on DNA and RNA

Includes: explanations, diagrams, images and charts

Content: nucleic acids, Dna, Rna, comparison, DNA replication

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  • Created by: Abbie_Mac
  • Created on: 18-03-13 20:10
Preview of OCR AS Biology- DNA and RNA

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Nucleic Acids
DNA is made up of nucleotides that contain a phosphate, base and a sugar
DNA is a polynucleotide ­ it is made up of lots of nucleotides
joined together.
Each nucleotide contains a deoxyribose sugar, a nitrogen
base and a phosphate group.
Every nucleotide has the same deoxyribose sugar and
phosphate group, but the base varies.
There are four different bases, Adenine (A), Thymine (T),
Guanine (G) and Cytosine (C).
Adenine and Guanine are both bases called purines and
Thymine and Cytosine are bases called pyrimidines.
Two polynucleotide strands join together to form a double helix
Nucleotides join together to form a polynucleotide strand.
Hydrogen bonds form between the bases holding together a polynucleotide
Each base can only pair with one particular partner ­ complementary base
Adenine (A) always pairs up with Thymine (T), (A-T) and Guanine (G) always
pairs up with Cytosine (C), (C-G).
There are two hydrogen bonds between Adenine and Thymine and three
hydrogen bonds between Cytosine and Guanine.
Two anti-parallel polynucleotide strands twist to form the DNA double helix.

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DNA replicates itself before cell division so that each new cell has the full amount of
1 Hydrogen bonds between the two
polynucleotide strands breaks, catalysed
by DNA Polymerase. The helix unzips to
form two single strands.
2 The original single strands act as a
template for a new strand. Free floating
DNA nucleotides join to the exposed
bases on the original single strand by
complementary base pairing.…read more

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Sugar-phosphate backbone with covalent phosphodiester bonds give strength
Sequence of bases allows information to be stored and as DNA is a long molecule,
it can store large amounts of information
Complementary base pairing enables information to be replicated and transcribed
Double helix protects weak hydrogen bonds and makes the molecule stable
Hydrogen bonding allows chains to split for replication or transcription and the
many hydrogen bonds together give the molecule stability.…read more

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The nucleotides form a polynucleotide Uracil (U) replaces Thymine (T) in RNA.
strand that is joined from the sugar of Uracil pairs up with Adenine.
one nucleotide to the phosphate of
another nucleotide.
Messenger RNA transfers the complementary DNA code out of the nucleus through a
nuclear pore to the ribosome for protein synthesis. mRNA carries the genetic code from
the DNA in the nucleus to the ribosomes in the cytoplasm where the proteins are made.…read more


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