PROTEIN SYNTHESIS

RNA (RIBONUCLEIC ACID)Nucleic acid involved in the synthesis

of proteins

RNA STRUCTUREComposed of nucleotides, but differs 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.

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 TRANSCRIPTIONNucleus

HOW TRANSCRIPTION OCCURS1. RNA polymerase untwists and unzips a

section of DNA (usually a single gene) from a chromosome.

2. RNA polymerase pairs free RNA nucleotides 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 TRANSCRIPTIONmRNA strand with instructions for building a

protein that leaves the nucleus and goes to the cytoplasm.

TRANSCRIPTION EXAMPLE• Transcribe 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• order 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 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 CODONS• AUG = start translation (Met)• UAA, UAG, UGA= stop translation

TRANSLATIONInstructions in mRNA are used to build a

protein

LOCATION OF TRANSLATIONribosome (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. tRNA’s continue lining up amino acids

according to codons6. peptide bonds link amino acids together7. ribosome reaches STOP codon• Amino acid chain is released

RESULT OF TRANSLATIONA Protein

What’s the point of all this?Gene Expression is all about protein

synthesis. Many of our genetic traits (hair color, eye color, skin color, height, metabolism) are based on the type of proteins that are made.