Chapter 12DNA & RNA

Section 12-3Section 12-3RNA & Protein SynthesisRNA & Protein Synthesis

Types of RNA

RNA Used For Protein SynthesisRNA Used For Protein Synthesis

Three Types of RNAThree Types of RNAMessenger RNA, mRNAMessenger RNA, mRNA

Ribosomal RNA, rRNARibosomal RNA, rRNA

Transfer RNA, tRNATransfer RNA, tRNA

Types of RNA

mRNAmRNATemplate to construct protein. It brings the Template to construct protein. It brings the

message from the DNA to the ribosomemessage from the DNA to the ribosome..

rRNArRNAPart of ribosome structurePart of ribosome structure

tRNAtRNATransports amino acids from cytoplasm to the Transports amino acids from cytoplasm to the

ribosomesribosomes

Transcription

The process of copying part of the DNA The process of copying part of the DNA nucleotide sequence into a nucleotide sequence into a

complementary sequence of RNAcomplementary sequence of RNA

Transcription

Requires the enzyme Requires the enzyme RNA PolymeraseRNA Polymerase

Step 1. Step 1. RNA polymerase binds to RNA polymerase binds to DNA and separates the DNA DNA and separates the DNA strands. strands.

Step 2.Step 2. RNA Polymerase uses one RNA Polymerase uses one strand of DNA as a template to strand of DNA as a template to polymerize nucleotides into RNApolymerize nucleotides into RNA

RNA Editing

After Making mRNA After Making mRNA IntronsIntronsAre Snipped OutAre Snipped Out

Exons Exons Remain, Remain,

(active segments of (active segments of nucleotides)nucleotides)

The Genetic Code

Proteins are long chains of amino acids.Proteins are long chains of amino acids.

There are 20 different amino acidsThere are 20 different amino acids

The order of amino acids in the protein The order of amino acids in the protein determine its shape and functiondetermine its shape and function

The Genetic Code

There are There are 20 amino acids20 amino acids but only but only4 bases4 bases in RNA in RNA

AdenineAdenine AACytosineCytosine CC

Guanine Guanine GGUracil Uracil UU

The Genetic Code

The genetic code consists of The genetic code consists of “words” three bases long“words” three bases long

Each “word” is called a Each “word” is called a Codon:Codon:three consecutive nucleotides that three consecutive nucleotides that

specifies a single amino acidspecifies a single amino acid

The Genetic Code

For ExampleFor Example::

UCGUCGCACCACGGUGGU = RNA Sequence = RNA SequenceUCGUCG--CACCAC--GGUGGU = Codons = Codons

UCGUCG codes for Serine codes for SerineCACCAC codes for Histidine codes for HistidineGGUGGU codes for Glycine codes for Glycine

Code Wheel

The Genetic Code

4 Bases4 Bases

CodonsCodons Defined with Defined with 3 Bases3 Bases

There Are 64 PossibleThere Are 64 Possible

3-base codons3-base codons

Since there are only 20 amino acids, Since there are only 20 amino acids, some amino acids are represented by some amino acids are represented by

multiple codonsmultiple codons

Translation

TranslationTranslation is the process of of is the process of of decoding the mRNA into a decoding the mRNA into a

polypeptide chainpolypeptide chain

• RibosomesRibosomes–Read mRNA and construct the Read mRNA and construct the

proteinsproteins

Translation Step 1

• mRNA leaves the NucleusmRNA leaves the Nucleus

Translation Step 2• mRNA binds to the ribosome. tRNA attachesmRNA binds to the ribosome. tRNA attaches• Anticodons on the tRNA line up with codons on mRNA The other end of Anticodons on the tRNA line up with codons on mRNA The other end of

the tRNA is an amino acidthe tRNA is an amino acid

Translation Step 3

– Ribosome connects Ribosome connects the amino acids the amino acids together as they together as they come into the come into the ribosomeribosome

Translation

• Step 4Step 4– A polypeptide A polypeptide

(Chain of Amino (Chain of Amino Acids) is formed. Acids) is formed.

– Polypeptide chain Polypeptide chain grows until the grows until the mRNA STOP Codon mRNA STOP Codon is reachedis reached

The Roles of RNA & DNA

DNADNA = =

Master PlanMaster Plan

RNARNA = =

Blueprints of the Master PlanBlueprints of the Master Plan

Proteins

• At the end of translation a protein At the end of translation a protein is formed.is formed.

• Proteins are enzymes that catalyze Proteins are enzymes that catalyze and regulate chemical reactionsand regulate chemical reactions

• Proteins can also be structural.Proteins can also be structural.