Protein SynthesisProtein Synthesis

RNA (RIBONUCLEIC ACID) Nucleic acid involved in the

synthesis of proteins Subunits are nucleotides Nucleotides are composed of

ribose sugar, phosphate and a nitrogen base

RNA STRUCTUREDiffers from DNA in three ways.

1. Single strand of nucleotides instead of double stranded

2. Has uracil instead of thymine3. Contains ribose instead of

deoxyribose

RNA FUNCTIONThree forms of RNA involved in

protein synthesis1. mRNA (messenger): copies

instructions in DNA and carries these to the ribosome.

2. tRNA (transfer): carries amino acids to the ribosome.

3. rRNA (ribosomal): composes the ribosome.

COMPARING DNA AND RNA

DNARNA

Role Complete instructions for making proteins

Transfer of information-protein production

Type of molecule Nucleic acid Nucleic acid

Building Blocks Nucleotides Nucleotides

Strand # 2 1

Sugar deoxyribose ribose

Location Nucleus NucleusCytoplasm

Nitrogen Base Pairs

ACTG ACUG

Types Only one mRNArRNAtRNA

PROTEIN SYNTHESISCells build proteins following instructions coded in genes (DNA).

Consists of two parts, transcription and translation

TRANSCRIPTIONDNA is copied into a complementary

strand of mRNA.

WHY? DNA cannot leave the nucleus.

Proteins are made in the cytoplasm. mRNA serves as a “messenger” and carries the protein building instructions to the ribosomes in the cytoplasm.

LOCATION OF TRANSCRIPTION

Nucleus

HOW TRANSCRIPTION OCCURS1. DNA unzips (usually a single gene) from a chromosome.2. Free RNA nucleotides are paired to the exposed bases of

one of the DNA strands following base pair rules. Uracil replaces thymine Only 1 strand of DNA serves as a template, the other

“hangs out”3. Newly synthesized mRNA separates from template DNA

and DNA zips back up.

RESULT OF TRANSCRIPTION

mRNA strand with instructions for building a protein that leaves the nucleus and goes to the cytoplasm.

TRANSCRIPTION EXAMPLETranscribe the following DNA Sequence in mRNA

TAC CGG ATC CTA GGA TCA AUG GCC UAG GAU CCU AGU

PROTEINSStructural and functional

components of organisms.Composed of amino acids

with peptide boundsorder of nucleotides in DNA

determines order of amino acids in a protein

One gene codes for one protein

GENETIC CODEThe “language” that

translates the sequence of nitrogen bases in DNA (mRNA) into the amino acids of a protein. Codon = three nucleotides

on DNA or mRNA One codon specifies one

amino acid Some codons are

redundant (code for the same amino acid)

The genetic code is universal to all organisms

DNA: TAC CTT GTG CAT GGG ATCmRNA AUG GAA CAC GUA CCC UAGA.A MET G.A HIS VAL PRO STOP

IMPORTANT CODONSAUG = start translation (Met)UAA, UAG, UGA= stop translation

TRANSLATIONInstructions in mRNA are used to build a protein

LOCATION OF TRANSLATION

ribosome (in the cytoplasm)

PROCESS OF TRANSLATION1. mRNA binds to the ribosome.2. Ribosome searches for start codon (AUG)3. tRNA brings correct amino acid

(methionine) to the ribosome. Each tRNA carries one type of amino acid. The anticodon (three nitrogen bases on tRNA) must

complement codon for amino acid to be added to protein chain

4. ribosome reads next codon5. tRNAs continue lining up

amino acids according to codons

6. peptide bonds link amino acids together

7. ribosome reaches STOP codon Amino acid chain is released

Practice online

http://learn.genetics.utah.edu/content/begin/dna/transcribe/