Transcript DNA AND PROTEIN SYNTHESIS

Protein 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 STRUCTURE
Differs from DNA in three ways.
1. Single strand of nucleotides
instead of double stranded
2. Has uracil instead of thymine
3. Contains ribose instead of
deoxyribose
RNA FUNCTION
Three forms of RNA involved in protein
synthesis
1. 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
DNA
RNA
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
Nucleus
Cytoplasm
Nitrogen Base Pairs
ACTG
ACUG
Types
Only one
mRNA
rRNA
tRNA
PROTEIN SYNTHESIS
Cells build proteins following
instructions coded in genes
(DNA).
 Consists of two parts,
transcription and translation
TRANSCRIPTION
DNA 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 OCCURS
1. 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 EXAMPLE
 Transcribe the following DNA
Sequence in mRNA
TAC CGG ATC CTA GGA TCA
AUG GCC UAG GAU CCU AGU
PROTEINS
Structural and functional
components of organisms.
 Composed of amino acids with
peptide bounds
 order of nucleotides in DNA
determines order of amino acids
in a protein
 One gene codes for one protein
GENETIC CODE
The “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 ATC
mRNA AUG GAA CAC GUA CCC UAG
A.A
MET G.A HIS VAL PRO STOP
IMPORTANT CODONS
 AUG = start translation (Met)
 UAA, UAG, UGA= stop translation
TRANSLATION
Instructions in mRNA are
used to build a protein
LOCATION OF
TRANSLATION
ribosome (in the cytoplasm)
PROCESS OF TRANSLATION
1. 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 codon
5. 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/t
ranscribe/