Download DNA and the Genome

Structure and function of
RNA
Unit 1: DNA and the Genome
RNA
There is a second type of nucleic acid in
the cell, called RNA.
RNA plays a vital role in the production of
protein from the code in the DNA.
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DNA and
the
Genome
Differences between DNA and RNA
RNA nucleotides are similar in
structure to DNA, except Ribose
sugar replaces Deoxyribose sugar…
5’ end
Phosphate
3’ end
… and Uracil
replaces thymine
Ribose
Sugar
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5’ pronounced
“5 prime”
DNA and
the
Genome
CFE Higher Biology
DNA and
the
Genome
DNA
RNA
Double stranded
Single stranded
Deoxyribose sugar
Ribose sugar
Bases: A, T, C and G
Bases: A, U*, C and G
*Uracil replaces
thymine
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DNA and
the
Genome
Types of RNA
There are three types of RNA:
1. Messenger RNA (mRNA)
2. Transfer RNA (tRNA)
3. Ribosomal RNA (rRNA)
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DNA and
the
Genome
mRNA
• mRNA is formed in the
nucleus from free
nucleotides and carries
a copy of the DNA code
from the nucleus to the
ribosomes (where
protein synthesis
occurs).
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RNA nucleotide
Phosphate
Organic Base
Ribose Sugar
DNA and
the
Genome
tRNA
tRNA molecules collect
amino acids and bring
them to the ribosome
to build proteins.
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DNA and
the
Genome
rRNA
• rRNA molecules
combine with proteins
to create the ribosome
– the organelle
responsible for
assembling proteins
following the DNA
code.
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The Ribosome
Blue = Proteins
Orange = rRNA subunit 1
Yellow = rRNA subunit 2
DNA and
the
Genome
Transcription
Unit 1: DNA and the Genome
Protein synthesis – Prior KU
What is a gene?
A gene is a section of DNA which
carries the code for the production of
one protein.
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DNA and
the
Genome
Protein synthesis
• We will look at the process of protein
synthesis in detail…
Click here for an overview of
protein synthesis
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DNA and
the
Genome
Nucleus
DNA
Overview
of gene
expression
AGAGGTTGACGAA
T CT CCAACTGCTT
Transcription
mRNA
U CU CCAACUGCUU
codon
Ribosome
ser
pro
thr
Translation
Protein
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DNA and
the
Genome
ala
Transcription
• Transcription is the synthesis of mRNA
from a section of DNA.
• Transcription of a gene starts from a
region of DNA known as the promoter.
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DNA and
the
Genome
Promoter: Start
of a gene
Terminator: End
of a gene
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DNA and
the
Genome
RNA polymerase
• This enzyme is responsible for
transcription.
• RNA polymerase binds at the promoter
and unwinds the DNA.
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DNA and
the
Genome
• RNA polymerase adds nucleotides onto
the 3’ end of the growing mRNA
molecule.
• Due to the base-pairing rules the mRNA
produced will be complementary to the
DNA.
• The molecule elongates until it reaches
the terminator sequence.
• The molecule produced is called the
primary transcript.
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DNA and
the
Genome
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DNA and
the
Genome
Modification of the primary
transcript
• Not all the regions in a eukaryotic gene
are required to produce the final
protein.
• These non-coding regions are called
introns.
• The coding regions are called exons.
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DNA and
the
Genome
Primary
Primary
transcript
transcript
Mature
transcript
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DNA and
the
Genome
RNA splicing
After the mRNA has been transcribed
the introns are removed.
The remaining exons are spliced together
to form a continuous sequence.
This is called the mature transcript.
The mature transcript then leaves the
nucleus to travel to the cytoplasm.
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DNA and
the
Genome