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/