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Ribonucleic Acid
RNA
The structure of ribonucleic acid
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Learning Objectives:
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Describe the structure of ribonucleic acid (RNA)
Describe the structure and role of messenger
RNA (mRNA)
Describe the structure and role of transfer RNA
(tRNA)
Describe the structure and role of ribosomal RNA
(rRNA)
RNA
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RNA = ribonucleic acid
RNA is a single -stranded polymer
Each RNA nucleotide consists of:
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A pentose sugar (ribose)
A phosphate group
A base – adenine, cytosine, guanine,
uracil (instead of thymine)
RNA used in protein synthesis is
messenger RNA (mRNA) or transfer
RNA (tRNA).
RNA contains the pentose sugar
ribose.
DNA contains the pentose sugar
deoxyribose.
The Genetic Code
(recap)
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3 nucleotide bases on mRNA (a codon) codes for
each amino acid in a protein (DNA = triplet code).
A few amino acids have a single codon.
The code is degenerate – most amino acids have
more than one codon.
3 codons code for no amino acids – they are stop
codons and mark the end of the polypeptide chain.
Non-overlapping – each nucleotide is read only
once.
Universal – same codon codes for the same amino
acid in all organisms (few minor exceptions).
mRNA (m = messenger)
tRNA (t = transfer)
Amino
acid joins
here
Anticodon
Complete the worksheet…
DNA + RNA Comparison
Messenger RNA (mRNA)
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Used to transfer the DNA code from the nucleus
to the cytoplasm, 1 gene at a time.
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Complementary to the DNA code.
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Small enough to leave the nuclear pores.
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Once in the cytoplasm, mRNA associates with
the ribosomes.
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Easily broken down and only exists whilst it is
needed to manufacture a protein.
Transfer RNA (tRNA)
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Small molecule (~80 nucleotides).
Single stranded and folded into a clover leaf shape
with one end of the chain slightly longer.
This longer section is attached to an amino acid.
Each tRNA carries a different amino acid.
3 bases at the opposite end of the tRNA are called
an anticodon.
Each amino acid has a different anticodon.
The anticodon pairs with the complementary codon
on the mRNA.
Ribosomal RNA (rRNA)
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Ribosomes are small organelles,
consisting of two subunits
The large subunit consists of 2 strands of
rRNA and 34 protein molecules
The small subunit consists of 1 strand of
rRNAand 21 protein molecules
The ribosome is roughly equal parts RNA and protein in
terms of mass
Eukaryotic ribosomes are slightly larger than prokaryotic
ribosomes (80S compared to 70S)
The ribosome is the site of protein synthesis