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Biology 3
Transcription, Translation, and
Mutations
Dr. Terence Lee
Overview
1. DNA and RNA structure
2. DNA replication
3. Transcription
– makes RNA
4. Translation
– makes protein
James Watson,
Francis Crick,
and Rosalind
Franklin
discovered the
structure of
DNA
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Image of DNA
DNA Structure
• Deoxyribonucleic acid (DNA) is
a type of nucleic acid
• Three parts:
1. Sugar group (deoxyribose)
2. Phosphate group
3. Nitrogenous base
• Adenine
• Guanine
• Thymine
• Cytosine
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���� DNA provides the instructions for building virtually every organism on earth!
The protein, influenced by the environment and in somecases other genes, then produces the trait.
Central Central Dogma of Biology
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DNA Replication
• Process by which a cell makes another copy
of its DNA
• Pairing Rules:
– A = T
– G = C
• The structure of DNA is a
double helix
• Shaped like a twisting ladder
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RNA Structure
• Ribonucleic acid (RNA) is a type of nucleic acid
• Three parts
1. Sugar group (ribose)
2. Phosphate group
3. Nitrogenous base
• Adenine
• Guanine
• Uracil
• Cytosine
How is RNA different from DNA?
1. Ribose has –OH group
2. RNA has uracil instead of thymine
3. RNA is a single strand
4. DNA stays in nucleus
5. RNA is made from DNA in nucleus and then
moves to cytoplasm.
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HOW GENES WORK: AN OVERVIEWTRANSCRIPTIONThe sequence for a gene is copied from DNA to a middleman molecule called mRNA.
TRANSLATIONThe sequence for a gene, now encoded in mRNA, is used to direct the production of a protein.
Inside nucleus Cytoplasm
Genes
Nuclearpore
DNAmRNA
Protein molecule
Grandmother’scookbook
Copying cookierecipe to index card
Index cardwith recipe
Chocolatechip cookies
Combining andbaking ingredient
Transcription
• Transcription is the process of using DNA
as a template to synthesize RNA.
– 1.) The DNA strands separate.
– 2.) RNA Polymerase reads the DNA and builds
the RNA strand.
– 3.) Three types of RNA can be made:
1. mRNA – messenger RNA
2. rRNA – ribosomal RNA
3. tRNA – transfer RNA
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• Promoter sequence – specific sequences of DNA that
the RNA Polymerase recognizes.
• Protein code – the DNA sequence that holds the genetic
material to create each protein.
• Termination sequence – Tells the RNA Polymerase to
stop transcription.
TRANSCRIPTION
RECOGNIZE and BINDOnce RNA polymeraserecognizes a promoter site,it binds to one strand of theDNA and begins readingthe gene’s message.
TRANSCRIBEAs the DNA strand is processed through the RNA polymerase, the RNA polymerase builds a single-strand copy of the gene, called the mRNA transcript.
TERMINATEWhen the RNA polymeraseencounters a code signalingthe end of the gene, it stopstranscription and releasesthe mRNA transcript.
CAPPING and EDITINGBefore the mRNA transcript can be translated into a protein, a cap and tail are often added for protection and to promote recognition, and non-coding sections are removed.
As the RNA polymerase moves down the strand of DNA, the helix unwinds so that the DNA can be read. At the same time, the DNA that has already been transcribed rewinds back to its original double-helix form.
UNWIND and REWIND
mRNA transcript leaves nucleus
to be translated into a protein.
RNApolymerase
DNA
mRNA
transcript
Tail
Cap Non-protein-coding
regions of mRNA
RNApolymerase
Promoter site
RNApolymerase
Termination site
mRNA transcript
Helix unwinds
Helix unwinds
21 3
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Translation
• Translation is the process of using the information in
mRNA to direct protein synthesis.
• Relies on sets of 3 nucleotides called codons.
• Each codon codes for a specific amino acid.
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Translation
• Ribosome
– 2 subunit non-membrane
organelle
– Holds the mRNA and tRNA
during protein formation
• tRNA
– Transfer RNA
– Reads the codons and finds
the correct amino acids.
Translation
1. Initiation
2. Elongation
3. Termination
Translation
• Initiation:
1. Ribosome small subunit binds to mRNA
2. Finds the start codon
3. The tRNA binds to the codon and brings the first
amino acid
4. The large subunit joins the small subunit and
protein formation can begin.
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Translation
• Elongation:
1. A new tRNA arrives and reads the codon.
2. The next amino acid arrives and binds to the
previous amino acid.
3. The process continues until a polypeptide
(protein) is formed.
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Translation
• Termination:
– Occurs when the ribosome reaches a stop codon.
– The two subunits come apart.
– The mRNA is released.
Summary of Protein Synthesis
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5.4 Not all DNA contains instructions for making proteins.
The Proportion of the DNA That Codes for Genes
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Introns and Exons
• Portions of the mRNA are removed before
translation.
Mutations
• Point Mutation – change in a single nucleotide of the
DNA sequence.
• Insertions and Deletions – changes one or more
nucleotides in the DNA sequence.