Transcript Ch.10 Notes - Green Local Schools

DNA, RNA, & Protein
Synthesis
Ch.10
(10-1) Discovery of DNA
• Griffith
– Transformation: transfer of genetic material
from 1 cell to another
• Avery
– Concluded DNA is responsible for
transformation in bacteria
• Hershey-Chase
– Used bacteriophages to conclude that DNA is
the hereditary molecule in viruses
Griffith & Avery
Hershey-Chase
(10-2) DNA
• Organic cmpd
• Made up of repeating subunits
(nucleotides)
• 2 long chains
Structure of DNA
• 3 parts:
1. Deoxyribose – sugar molecule
2. Phosphate group – PO433. Nitrogen-containing base – has N
atom
4 N-Containing Bases
1. Adenine (A)
2. Guanine (G)
3. Cytosine (C)
4. Thymine (T)
• Purines: 2 rings of C & N atoms
– A&G
• Pyrimidines: 1 ring of C & N atoms
– C&T
Double Helix
• Watson & Crick (1953) suggested
model
• Used Franklin & Wilkins’ x-ray photograph
“Backbone”
• Sugar & phosphate
covalently bonded
• Bases face center
& are
perpendicular to
backbone
• H-bonds hold
strands together
Complementary Base Pairing
• 2 rules:
1. C pairs w/ G
2. A pairs w/ T
• Nucleotide
sequence in 1
chain is
complement of
other chain
(10-3) DNA Replication
• Replication fork: area where chains
separate
• Helicase: enzyme that breaks H-bonds
b/w bases causing chains to separate
– Each chain serves as a template for a new
chain
DNA Polymerase
• Enzyme that binds to separated strands of
DNA & assembles each strand’s
complement
• Old: ATTCCG
• New: TAAGGC
Accuracy & Repair
• High accuracy
– Proofreading
– Repair enzymes
• Mutation: change in nucleotide sequence
– DNA can also be damaged by chemicals &
UV light
(10-4) RNA
• Ribonucleic acid
• 3 types: m, t, r
RNA Structure
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•
•
•
Repeating nucleotides
Single-stranded
Ribose: sugar molecule
Uracil replaces thymine
– U pairs w/ A
Messenger (mRNA)
•
•
Single, uncoiled chain
Carries genetic info from DNA in nucleus
to ribosomes in cytosol
Transfer (tRNA)
•
•
•
Single chain
Nucleotides folded into hairpin shape
Binds to specific amino acids (aa)
Ribosomal (rRNA)
•
•
•
Most abundant form
Globular
Make up ribosomes
Transcription
• Genetic info is copied from DNA to mRNA
(transcript)
• Occurs in nucleus
• Methylation: regulation of gene
expression & can stop transcription
– Leads to cell specialization
Steps of Transcription
1. RNA polymerase binds to promoter of a
specific gene
2. Complementary copy of 1 strand made
using RNA nucleotides (A w/ U, C w/ G)
3. Polymerase reaches termination signal &
transcription stops
Genetic Code
• Correlation b/w nucleotide & aa’s
– 20 different aa to make proteins (polypeptide)
• Used by most organisms to translate
mRNA transcripts into proteins
Codon
• 3 mRNA bases = 1 codon
– Codes for proteins
• Start codon: signal ribosome to start
translating mRNA
– AUG
• Stop codon: cause ribosome to stop
translating mRNA
– UAA, UAG, UGA
Translation (Protein Synthesis)
• Assembling proteins from info encoded in
mRNA
• Anticodon: tRNA segment complementary
to mRNA codon
Steps of Translation
1. Codon (mRNA) paired w/ anticodon
(tRNA)
2. tRNA adds specific aa to the growing
polypeptide chain
Ribosomes
• Free in cytosol & some attached to ER
• Binding sites for translation:
– Holds mRNA transcript
– Holds tRNA
Protein Assembly
1. Ribosome attaches to start codon on
mRNA transcript
•
Pairs w/ tRNA anticodon
2. Ribosomes move along mRNA
•
Aa continue to attach as anticodons paired
3. Ribosome reaches a
stop codon
•
mRNA is released &
protein is complete