Proteins are made by decoding the Information in DNA

Proteins are not built directly from DNA

A molecule called RNA – ribonucleic acid is used to decode the instructions in DNA,

RNA Structure

Like DNA, RNA is a nucleic acid.

RNA is a nucleic acid made up of repeating nucleotides

RNA differs from DNAin three different ways.

The sugar in RNA is ribose

RNA is single- stranded

RNA contains the base uracil instead of thymine.

Like thymine, uracil can form bonds with adenine

TranscriptionThe instructions for making a protein are transferred from a gene (DNA) to RNA

Transcription = DNA → RNA

Segment of DNA unwinds

DNA unzips

RNA is produced one nucleotide at a time by matching base pairs with the nucleotides in DNA.

After the synthesis is complete, the RNA separates from the DNA and the DNA recoils into its helix.

The RNA strand leaves the nucleus and goes into cytoplasm

In what part of the cell does transcription take place?

RNA makes proteins.

Where are proteins made in the cell?

Forms of RNA

Messenger RNA - mRNA

mRNA carries the information to the cytoplasm where the ribosomes can make it into protein.

– "Blueprint" for protein synthesis that is transcribed from one strand of the DNA (gene) and which is translated at the

ribosome into a polypeptide sequence.

Ribosomes take RNA coded information and "translate" that information into chains of amino acids called pollypeptides

A protein is made up of one or more polypeptide chains.

Ribosomal rRNA

• a structural component of the ribosome.

tRNA molecule that converts nucleic acid sequence to protein sequence

tRNA - transfer RNA • It acts as an adaptor to carry the amino acid

elements of a protein to the appropriate place as coded for by the mRNA.

Small, single-stranded RNA molecules that bind to amino acids and deliver them to the proper codon on messenger RNA.

Messenger RNA (mRNA) is the blueprint for construction of a protein.

Ribosomal RNA (rRNA) is the construction site where the protein is made.

Transfer RNA (tRNA) is the truck delivering the proper amino acid to the site at the right time.

Translation

The ribosome reads the mRNA sequence and translates it (or decodes it) into an amino acid sequence in a polypeptide.

Polypeptides are chains of amino acids.

Proteins are made up of one or more polypeptide molecules.

So….the building block of proteins are ___________________.

There are 20 essential amino acids that make up proteins.

The instructions in DNA specify the order in which the amino acids are put together.

RNA – contains 4 different nucleotides.(Language – 4 letters)

How can a code with only 4 letters carry instructions for 20 amino acids?

# of letters # of words

1 4

2 16

3 64

The genetic code could signify 64 different words

The group of 3 nucleotides in mRNA that specifies an amino acid is known as a codon.

Think of codons as the words of the genetic message.

Example: The following sequence of nucleotides in mRNA

• AAACACGGU

Would be read as 3 codons

AAA- CAC-GGU

And each codon represents a different _____.

G

First Second Third

U C A G

U

UUUPhenylalanine

UCUSerine

UAUTyrosine

UGUCysteine U

UUCPhenylalanine

UCCSerine

UACTyrosine

UGCCysteine C

UUALeucine

UCASerine

UAASTOP

UGASTOP A

UUGLeucine

UCGSerine

UAGSTOP

UGGTryptophan G

C

CUULeucine

CCUProline

CAUHistidine

CGUArginine U

CUCLeucine

CCCProline

CACHistidine

CGCArginine C

CUALeucine

CCAProline

CAAGlutamine

CGAArginine A

CUGLeucine

CCGProline

CAGGlutamine

CGGArginine G

A

AUUIsoleucine

ACUThreonine

AAUAsparagine

AGUSerine U

AUCIsoleucine

ACCThreonine

AACAsparagine

AGCSerine C

AUAIsoleucine>

ACAThreonine

AAALysine

AGAArginine A

AUGMethionine

ACGThreonine

AAGLysine

AGGArginine G

GUUValine

GCUAlanine

GAUAspartic acid

GGUGlycine U

GUCValine

ValineAlanine

GACAspartic acid

GGCGlycine C

GUAValine

GCAAlanine

GAAGlutamic acid

GGAGlycine A

GUGValine

GCGAlanine

GAGGlutamic acid

GGGGlycine G

Page figure

Shows all 64 possible codons of the genetic code.

Notice: More than one codon can specify the same amino acid.

How do tRNAs recognize to which codon to bring an amino acid?

The tRNA has an anticodon that is complementary to the codon on the mRNA. Each tRNA only binds the appropriate amino acid for its anticodon

amino acids are carried by the molecules of tRNA.

The ribosomes “read” the codons in mRNA allowing tRNA molecules to bring the proper amino acid. (the anti-codon on tRNA bonds to the proper codon on mRNA)