UNIT 9

Protein Synthesis

RNA

Objective:

Compare and contrast DNA and RNA

State the three types of RNA and their

function.

Explain the function of RNA

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.

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.

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.

TYPES OF RNA

Types of RNA-

•There are three main types of RNA:

• messenger RNA- mRNA

• ribosomal RNA- rRNA

• transfer RNA- tRNA

TYPES OF RNA

Messenger RNA (mRNA) carries copies of instructions for assembling

amino acids into proteins.

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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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During protein construction, transfer RNA (tRNA) transfers each

amino acid to the ribosome.

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?

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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TRANSCRIPTION

Transcription

Goal: to make RNA

How:

• Copying part of a nucleotide sequence of DNA into a complementary sequence in RNA.

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.

ELONGATION

5'

RNApolymerase

3'

5'

Direction of transcript ion("downstream")

Templatestrand of DNA

'Newly madeRNA

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TRANSCRIBE THE F OL L OWING

DNA

ATCGCGTAC

GCTAGCTACT

TTACTAGCGG

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

TRANSLATION

Explain the goal of translation

Determine the correct amino acids when given a

codon

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).

A codon consists of three consecutive nucleotides on

mRNA that specify a particular amino acid.

• 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.

• 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.

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.

Nucleus

mRNA

•Messenger RNA is transcribed in the

nucleus, and then enters the cytoplasm

where it attaches to a ribosome.

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.

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.

LysinetRNAPhenylalanine

Methionine

Ribosome

mRNAStart codon

The ribosome binds new tRNA molecules and amino acids as it moves

along the mRNA.

•The process continues until the ribosome reaches a stop

codon.

Polypeptide

Ribosome

tRNA

mRNA

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.

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.

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.

The central dogma of molecular biology is that information is

transferred from DNA to RNA to protein.

THE GENETIC CODE

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

12-4 MUTATIONS

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.

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.

KINDS OF MUTATIONS

Substitutions usually

affect no more than a

single amino acid.

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.

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.

KINDS OF MUTATIONS

In an insertion, an extra

base is inserted into a base

sequence.

KINDS OF MUTATIONS

In a deletion, the loss of a single base is deleted and the

reading frame is shifted.

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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•Duplications produce extra copies of

parts of a chromosome.

Inversions reverse the direction of parts of

chromosomes.

Translocations occurs when part of one chromosome breaks off

and attaches to another.

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.