DNA mRNA Transcription Chapter 8 The Central Dogma of Molecular Biology Cell Polypeptide (protein)...
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Transcript of DNA mRNA Transcription Chapter 8 The Central Dogma of Molecular Biology Cell Polypeptide (protein)...
DNA
mRNA
Transcription
Chapter 8The Central Dogma
of Molecular Biology
Cell
Polypeptide(protein)
TranslationRibosome
DNA (DEOXYRIBONUCLEIC ACID)• Nucleic acid that composes
chromosomes and carries genetic information.
CHROMOSOME ORGANIZATION1. 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 DNAComposed of nucleotides• Nucleotides contain three parts:1. 5-Carbon Sugar (deoxyribose)2. Phosphate Group3. 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 bondsC-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 REPLICATIONProcess in which DNA is copied.PURPOSE OF DNA REPLICATIONGives daughter cells produced by cell division
a complete set of genetic information identical to the parent cell.
WHERE REPLICATION OCCURSNucleusWHEN DURING THE CELL CYCLE
REPLICATION OCCURSInterphase (S)
HOW REPLICATION OCCURS1. 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 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
DNA RNA
Double strand Single strand
A---Thymine A---Uracil
Deoxyribose Ribose
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 proteins (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.
Protein Synthesis: Transcription
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 (monomers).• 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 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
TRANSLATIONInstructions in mRNA are used to build a
protein
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
LOCATION OF TRANSLATIONribosome (in the cytoplasm)
RESULT OF TRANSLATIONA Protein
Protein Synthesis: Translation
SU
GA
R-P
HO
SP
HA
TE B
AC
KB
ON
E
B A
S E
S
H
P OO
HO
O
O
CH2NH2N
NHN
N
HOH
P
O
O
HO
O
O
CH2
NH2
N
NN
N
H
P
O
OH
HO
O
O
CH2
NH2
N
NN
N
O
A Codon
Guanine
Adenine
Adenine
Arginine
Protein Synthesis: Translation
Protein Synthesis: Translation
AELarge
subunit
P
Small subunit
Translation - Initiation
fMet
UACGAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA5’mRNA
3’
AERibosom
e
PUCU
Arg
Aminoacyl tRNAPhe
Leu
Met
SerGly
Polypeptide
CCA
Translation - Elongation
GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA5’mRNA
3’
AERibosom
e
P
PheLeu
Met
SerGly
Polypeptide
Arg
Aminoacyl tRNA
UCUCCA
Translation - Elongation
GAG...CU-AUG--UUC--CUU--AGU--GGU--AGA--GCU--GUA--UGA-AT GCA...TAAAAAA5’mRNA
3’
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