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RNA and Protein Synthesis
What is a gene?
A
region of DNA that contains
instructions for the making of
proteins.
chromosomes:
 fibers of DNA (chromatin)
and proteins
 contains all genetic
information for cell on genes
• genes contain information
for synthesis of proteins
• DNA is blueprint for
organization, development,
daily functioning of cell.
RNA
 Ribonucleic
 Function:
acid
moves the genetic
information from DNA in the
nucleus to the ribosome (site
of protein synthesis) in the
cytoplasm
RNA Structure


Formed by nucleotides
 Sugar – Ribose
 Phosphate group
 Nitrogenous Base
 Adenine
 Uracil (replaces thymine)
 Cytosine
 Guanine
Single-stranded
3 types of RNA
 Messenger
RNA (mRNA)
 Ribosomal
RNA (rRNA)
 Transfer
RNA (tRNA)
Messenger RNA (mRNA)
Structure
– single strand
Function
– carries genetic
information from DNA in
nucleus to the ribosome
Location
- nucleus
Piece of DNA that
has information to
make a specific protein
Rules of base-pairing apply for the mRNA
DNA
RNA must be
“complementary” to DNA
mRNA
-A
-T
-G
-C
-T
-A
UACGAU-
A always with U
C always with G
Making of the Mobile Messenger
Ribosomal RNA (rRNA)
Structure
– globular
Function
– makes up the
ribosome
Location
– ribosome
rRNA =
ribosomal RNA
 ”structural
work-bench” on
which proteins are
built
Transfer RNA (tRNA)
Shape
– hairpin (t-shaped)
Function
– carries
(transfers) amino acid to
ribosome
Location
ribosome
– cytoplasm to
tRNA = transfer RNA
1. picks
up one
specific amino
acid AND
2. pairs with
mRNA codon
specific for
that amino
acid only!
Protein Synthesis
2
stages
Transcription in the
nucleus
Translation
ribosome
in the
Transcription + Translation:
TRANSLATION
TRANSCRIPTION
Nucleus
DNA
Cytoplasm
RNA
Protein
Transcription
 Transferring
information from
DNA to mRNA
Codon
3
bases of mRNA nucleotides
Each codon codes for a
specific amino acid
Near universal – supports
idea that organisms are
related
Codons
Start
Codon – AUG
Stop
Codons – UAA, UAG,
UGA
These codons tell
translation to begin and end
Anticodon
3
bases of tRNA nucleotides
Complementary
to mRNA
codon
Located
on opposite end of
amino acid
Ribosome

Composed of rRNA with 3 binding
sites

Free in cytoplasm – proteins are used
in the cell

RER – makes proteins to be exported
out of the cell
DNA vs. RNA



DNA
5 Carbon Sugar =
Deoxyribose
Base Pairs = Adenine
Thymine
Guanine
Cytocine
Original copy of
genetic information



RNA
5 Carbon Sugar =
Ribose
Base Pairs = Adenine
Uracil
Guanine
Cytocine
Disposable copy of
genetic information
ribosome “reads” mRNA
codons one at a time
arginine
ANTICODONS
mRNA codons ...
protein =
lysine
proline
cysteine
G C G U U C G G G A C A
CG C A A G C C C U G U
How About An
Example?
DNA:
mRNA:
tRNA:
TGG CCA ATA
ACC GGU UAU
UGG CCA AUA
ACC= 20
GGU=12 UAU=13
Code for an Amino Acid Sequence!
Example = Hairy
Steps for Translation:
1. mRNA leaves nucleus to cytoplasm
- codons specify certain AA sequence
2. mRNA associates with ribosome which “reads” mRNA codons one at a time
• synthesis of proteins occur on ribosomes
3. tRNA with specific amino acid (corresponding to anticodon) carries
correct amino acid to mRNA + ribosomes
4. tRNA delivers correct amino acid (anticodon-codon base pairing) to
ribosome and leaves
5. polypeptide elongates in sequence directed by the mRNA codons
 formation of peptide bond between amino acids
6. termination reached at stop codon
 ribosome falls off
 polypeptide is released
Transcription
 Exons – coding regions of
DNA
 Introns – non-coding regions
of DNA
 Cut
out (spliced) which controls the
genetic information that leaves the
nucleus