unit 9 - ddtwo.org
TRANSCRIPT
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UNIT 9
Protein Synthesis
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RNA
Objective:
Compare and contrast DNA and RNA
State the three types of RNA and their
function.
Explain the function of RNA
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12–3 RNA AND PROTEIN
SYNTHESIS
Genes are coded DNA instructions that control
the production of proteins.
Genetic messages can be decoded by copying part
of the nucleotide sequence from DNA into RNA.
RNA contains coded information for making
proteins.
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THE STRUCTURE OF RNA
The Structure of RNA-Ribonucleic Acid
RNA consists of a long chain of nucleotides.
Each nucleotide is made up of
1. a 5-carbon sugar, ribose
2. a phosphate group, and a
3. nitrogenous base.
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THE STRUCTURE OF RNA
There are three main differences between RNA
and DNA:
1. The sugar in RNA is ribose instead of
deoxyribose.
2. RNA is generally single-stranded.
3. RNA contains uracil in place of thymine.
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TYPES OF RNA
Types of RNA-
•There are three main types of RNA:
• messenger RNA- mRNA
• ribosomal RNA- rRNA
• transfer RNA- tRNA
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TYPES OF RNA
Messenger RNA (mRNA) carries copies of instructions for assembling
amino acids into proteins.
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Copyright Pearson Prentice Hall
Ribosomes are made up of proteins and ribosomal RNA (rRNA). Its
job is to hold on to the mRNA.
Ribosomal RNA
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Copyright Pearson Prentice Hall
During protein construction, transfer RNA (tRNA) transfers each
amino acid to the ribosome.
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CHECK FOR UNDERSTANDING
1. What does RNA stand for?
2. What are the monomers of RNA?
3. What is the sugar in RNA?
4. What is the shape of RNA?
5. What nitrogen base is found in RNA, but
not DNA?
6. What are the three types of RNA and
what is their function?
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TRANSCRIPTION
E X P L A I N T R A N S C R I P T I O N A N D W H Y I T
I S N E C E S S A R Y .
L I S T T H E S T E P S O F T R A N S C R I P T I O N .
T R A N S C R I B E A S E G M E N T O F D N A .
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Copyright Pearson Prentice Hall
TRANSCRIPTION
Transcription
Goal: to make RNA
How:
• Copying part of a nucleotide sequence of DNA into a complementary sequence in RNA.
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STEPS OF TRANSCRIPTION
1. DNA unwinds
2. DNA unzips
3. RNA nucleotides are added- the new RNA is complementary
NOT identical!!!
4. Once the RNA is complete it is released to the cytoplasm to
find an rRNA.
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ELONGATION
5'
RNApolymerase
3'
5'
Direction of transcript ion("downstream")
Templatestrand of DNA
'Newly madeRNA
CopyrightC Pearson Education, Inc., publishing as Benjamin Cummings.
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TRANSCRIBE THE F OL L OWING
DNA
ATCGCGTAC
GCTAGCTACT
TTACTAGCGG
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CHECK FOR UNDERSTANDING
1. What is the end product of transcription?
2. Where does transcription take place?
3. What type of RNA is produced during
transcription?
4. What is the first step of transcription?
5. Transcribe the following strand of DNA:
ATTCGAGGA
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TRANSLATION
Explain the goal of translation
Determine the correct amino acids when given a
codon
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THE GENETIC CODE
The Genetic Code
• The genetic code is the “language” of mRNA
instructions.
• The code is written using four “letters” (the bases:
A, U, C, and G).
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A codon consists of three consecutive nucleotides on
mRNA that specify a particular amino acid.
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• Each codon specifies a particular amino acid that is to be placed on the polypeptide chain.
• Some amino acids can be specified by more than one codon.
• There are 20 amino acids.
• Different amino acids are joined together to produce polypeptides.
• There are 64 possible base codons.
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• There is one codon AUG that can either specify the
amino acid methionine or serve as a “start” codon
for protein synthesis.
• There are three “stop” codons that do not code for
any amino acid. These “stop” codons signify the
end of a polypeptide.
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TRANSLATION
•Translation is the decoding of an mRNA message into a
polypeptide chain (protein).
•Translation takes place on ribosomes.
•During translation, the cell uses information from
messenger RNA to produce proteins.
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Nucleus
mRNA
•Messenger RNA is transcribed in the
nucleus, and then enters the cytoplasm
where it attaches to a ribosome.
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TRANSLATION
Translation begins when an mRNA molecule attaches to a
ribosome.
As each codon of the mRNA molecule moves through the
ribosome, the proper amino acid is brought into the ribosome by
tRNA.
In the ribosome, the amino acid is transferred to the growing
polypeptide chain.
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TRANSLATION
Each tRNA molecule carries only one kind of amino acid.
In addition to an amino acid, each tRNA molecule has three
unpaired bases.
These bases, called the anticodon, are complementary to
one mRNA codon.
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LysinetRNAPhenylalanine
Methionine
Ribosome
mRNAStart codon
The ribosome binds new tRNA molecules and amino acids as it moves
along the mRNA.
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•The process continues until the ribosome reaches a stop
codon.
Polypeptide
Ribosome
tRNA
mRNA
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THE ROLES OF RNA AND
DNA
The Roles of RNA and DNA
• The cell uses the DNA “master plan” to prepare
RNA “blueprints.” The DNA stays in the nucleus.
• The RNA molecules go to the protein building
sites in the cytoplasm—the ribosomes.
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GENES AND PROTEINS
Genes and Proteins
• Genes contain instructions for assembling
proteins.
• Many proteins are enzymes, which catalyze and
regulate chemical reactions.
• Proteins are each specifically designed to build or
operate a component of a living cell.
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The sequence of bases in DNA is
used as a template for mRNA.
The codons of mRNA specify
the sequence of amino acids in a
protein.
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The central dogma of molecular biology is that information is
transferred from DNA to RNA to protein.
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THE GENETIC CODE
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CHECK FOR U NDER STANDING
1. Where does translation take place?
2. What is a codon?
3. What is an anticodon?
4. ID the 3rd codon in the sequence:
AUUGGGCGUAAU
6. What is the anticodon for AAA?
7. How many amino acids are there?
8. Use the table and ID the amino acids for the
following codons: AUG and CUU
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12-4 MUTATIONS
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12-4 MUTATIONS
•Mutations are changes in the genetic material.
Kinds of Mutations
• Gene mutations- Mutations that produce changes in a single gene.
• Chromosomal mutations-Mutations that produce changes in whole chromosomes.
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KINDS OF
MUTATIONS
•Gene Mutations
•Gene mutations involving a change in
one or a few nucleotides are known as
point mutations because they occur at a
single point in the DNA sequence.
•Point mutations include substitutions,
insertions, and deletions.
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KINDS OF MUTATIONS
Substitutions usually
affect no more than a
single amino acid.
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The effects of insertions or deletions are more
dramatic.
The addition or deletion of a nucleotide causes a
shift in the grouping of codons.
Changes like these are called frameshift
mutations.
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Frameshift mutations may change every amino
acid that follows the point of the mutation.
Frameshift mutations can alter a protein so much
that it is unable to perform its normal functions.
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KINDS OF MUTATIONS
In an insertion, an extra
base is inserted into a base
sequence.
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KINDS OF MUTATIONS
In a deletion, the loss of a single base is deleted and the
reading frame is shifted.
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CHROMOSOMAL MUTATIONS
• Chromosomal mutations involve changes
in the number or structure of
chromosomes.
• Chromosomal mutations include deletions,
duplications, inversions, and
translocations.
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Copyright Pearson Prentice Hall
•Duplications produce extra copies of
parts of a chromosome.
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Inversions reverse the direction of parts of
chromosomes.
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Translocations occurs when part of one chromosome breaks off
and attaches to another.
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SIGNIFICANCE OF MUTATIONS
• Many mutations have little or no effect on gene
expression.
• Some mutations are the cause of genetic disorders.
• Beneficial mutations may produce proteins with
new or altered activities that can be useful.
• Polyploidy is the condition in which an organism
has extra sets of chromosomes.