Transcript dna and protein synthesis

Chapter 8
The Central Dogma
of Molecular Biology
Cell
DNA
Transcription
mRNA
Translation
Ribosome
Polypeptide
(protein)
DNA (DEOXYRIBONUCLEIC ACID)
• Nucleic acid that composes
chromosomes and carries genetic
information.
CHROMOSOME ORGANIZATION
1. A chromosome is an enormous strand of
super coiled DNA.
2. Sections of DNA on the chromosome that
code for proteins are called genes.
3. Noncoding sections of DNA are called
“junk DNA” (regulatory or unknown
function)
BUILDING BLOCKS OF DNA
Composed of nucleotides
• Nucleotides contain three parts:
1. 5-Carbon Sugar (deoxyribose)
2. Phosphate Group
3. Nitrogen Base (four types, adenine,
guanine, thymine and cytosine)
• Adenine and Guanine are purines
(composed of two rings of nitrogen atoms)
• Thymine and Cytosine are pyrimidines
(composed of one ring of nitrogen atoms)
STRUCTURE OF DNA
• Consists of two strands of nucleotides that
form a twisted ladder (double helix)
• Sugar and phosphate alternate along the
sides of the ladder (linked by strong
covalent bonds)
• Pairs of nitrogen bases form the rungs of
the ladder (linked by weak hydrogen
bonds).
• Specific base pairing arrangement
(Chargaff’s Rule)
A-T : 2 hydrogen bonds
C-G : 3 hydrogen bonds
• Nitrogen bases attach to the sugar portion
of the side (NOT the phosphate)
• Strands run in opposite directions
FUNCTION OF DNA
• DNA codes for proteins (structural
proteins, enzymes, and hormones)
• information for building proteins is carried
in the sequence of nitrogen bases
• proteins determine physical and metabolic
traits and regulate growth and
development.
DNA REPLICATION
Process in which DNA is copied.
PURPOSE OF DNA REPLICATION
Gives daughter cells produced by cell division
a complete set of genetic information
identical to the parent cell.
WHERE REPLICATION OCCURS
Nucleus
WHEN DURING THE CELL CYCLE
REPLICATION OCCURS
Interphase (S)
HOW REPLICATION OCCURS
1. Helicase enzymes unzip the parent
strand by separating the nitrogen base
pairs.
2. DNA polymerase pairs free DNA
nucleotides with the exposed bases on
both strands following the base pair rules.
• each strand from the parent molecule
serve as a template
3. Hydrogen bonds reform spontaneously
sealing the two strands of each DNA
molecule together.
RESULTS OF REPLICATION
• Two molecules of DNA that are identical
• Each is half old (strand from parent) and
half new (strand synthesized by DNA
polymerase)
RNA (RIBONUCLEIC ACID)
Nucleic acid involved in the synthesis
of proteins
RNA STRUCTURE
Composed of nucleotides, but 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
DNA
RNA
Double strand
Single strand
A---Thymine
A---Uracil
Deoxyribose
Ribose
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 proteins
(ribosome).
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. 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.
Protein Synthesis:
Transcription
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 (monomers).
• 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
TRANSLATION
Instructions in mRNA are used to build a
protein
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. tRNA’s 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
LOCATION OF TRANSLATION
ribosome (in the cytoplasm)
RESULT OF TRANSLATION
A Protein
Protein Synthesis: Translation
A Codon
OH
P
HO
NH2
O
N
O
CH2
N
H
P
O
O
N
O
CH2
P
NH
N
Guanine
NH2
N
O
Arginine
H
O
HO
N
O
O
HO
Adenine
N
NH2
O
N
O
CH2
N
O
OH
H
N
N
Adenine
Protein Synthesis: Translation
Protein Synthesis: Translation
Translation - Initiation
fMet
Large
subunit
P
A
E
UAC
5’GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA
Small mRNA
subunit
3’
Translation - Elongation
Polypeptide
Arg
Met
Phe
Leu
Ser
Aminoacyl tRNA
Gly
Ribosom
e
P
A
E
CCA
5’GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA
mRNA
3’
Translation - Elongation
Polypeptide
Met
Phe
Leu
Ser
Gly
Arg
Aminoacyl tRNA
Ribosom
e
P
A
E
CCA UCU
5’GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA
mRNA
3’
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