Revision Biology - Nucleic Acids

Revision for biology - nucleic acids. Spec: OCR

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Revision - Nucleic Acid
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 for 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.
RNA is similar to DNA
Similarities Differences
RNA and DNA both are made of nucleotides The sugar in RNA is ribose sugar, whereas in DNA
containing a sugar, phosphate group and a base. it's deoxyribose sugar.
RNA and DNA both contain one of the four RNA forms a single polynucleotide strand,
different bases. whereas DNA forms a double nucleotide strand.
The nucleotides form a polynucleotide strand Uracil (U) replaces Thymine (T) in RNA. Uracil pairs
that is joined from the sugar of one nucleotide to up with Adenine.
the phosphate of another nucleotide.
Two polynucleotide strands join together to form a double helix
Nucleotides join together to form a polynucleotide strand.
A polynucleotide strand is joined from the sugar of one nucleotide to the phosphate group of
another nucleotide.
Hydrogen bonds form between the bases holding together a polynucleotide strand.
Each base can only pair with one particular partner ­ complementary base pairing.
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.
Semi-Conservative Replication
DNA replicates itself before cell division so that each new cell has the full amount of DNA.
Hydrogen bonds between the two polynucleotide strands breaks. The helix unzips to form two
single strands.
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.
The nucleotides on the new strand are joined together by an enzyme called DNA polymerase.
Hydrogen bonds form between the bases on the original and new strands.
Each new DNA molecule has an original strand a new strand.
This type of copying is called Semi-Conservative Replication because half of the new DNA strands are
from the original strand of DNA.
DNA contains genes which are instructions for proteins
A gene is a sequence of DNA nucleotides that codes for a polypeptide.
Proteins are made up of amino acids.
Different proteins have different number and order of amino acids.
It's the order of the nucleotide bases that determines the order of amino acids in a protein.
Each amino acid is coded by a sequence of three bases in a gene.
Different sequences of bases code for different amino acids.

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DNA is copied into RNA for protein synthesis
All the reactions in organisms need proteins.
DNA carries the instructions to make proteins (as genes). It's found in the nucleus.
The organelles that make proteins are found in the cytoplasm. But the DNA molecules are too
large to move out of the nucleus.
So, sections of DNA are copied into RNA.
RNA leaves the nucleus and joins with a ribosome in the cytoplasm, where it can be used to
synthesise a protein.…read more


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