Download Section 12-1

Chapter 12:
DNA, RNA and Protein Synthesis
Name __________________
Section 12-1
I. Important DNA experiments
A. Griffith (1928) discovered transformation – genetic information
can be transferred from one living thing to another (fig. 12-2)
B. Avery (1944) discovered that DNA stores and transmits genetic
information
C. Hershey and Chase (1952) discovered that the genetic
information in a virus is DNA, not protein. (fig. 12-3 and 12-4)
II. Structure of DNA
A. DNA is made of nucleotides. (fig 12-5)
a. Nucleotides are made of a:
1. phosphate group
2. sugar
3. base (A = adenine; T = thymine; C = cytosine;
G = guanine)
B. Chargoff’s base-pairing rules: (fig 12-6)
a. Showed that the percentages of the bases A and T are
approximately equal and C and T are approximately equal
b. Therefore, in DNA, A pairs with T; C pairs with G
C. Rosalind Franklin (1952) used X-ray diffraction to study the
structure of DNA
D. Watson and Crick (1953) made a model of DNA (fig 12-7)
a. Showed that DNA was a double stranded molecule, called a
double helix
b. DNA is 2 strands of nucleotides wrapped around each other,
and connected by base pairs in the middle, forming a twisted
ladder shape
Section 12-2: DNA Replication
I. Chromosomes are made of DNA. Chromosomes must copy before a cell
can divide
Chromosome differences between prokaryotes and eukaryotes:
Prokaryotes
Eukaryotes
Chromosomes in cytoplasm
(no nucleus)
Chromosomes in nucleus
Contain 1 chromosome that is
circular
Contain many chromosomes
See figure 12-8
See figure 12-10
Chromosomes contain DNA wrapped
around proteins.
II. Chromatin – substance made of DNA wrapped around proteins. The
proteins are called histones.
III. Genes – sections of DNA that control protein production
IV. DNA replication – how DNA is copied
A. Steps of DNA replication:
1. DNA strands separate “unzip”
2. Two new strands form, called complementary strands
3. DNA polymerase forms the new strands
DNA replication follows the base pairing rules.
Example:
old strand: A T T A C G G G A A G C
new strand: T A A T G C C C T
TCG
Section 12-3: Protein Synthesis – how proteins are made
I. RNA reads the message in DNA and helps to make proteins
II. Differences between DNA and RNA:
DNA
RNA
Double stranded
Single stranded
Contains deoxyribose
sugar
Contains Thymine (T)
Contains ribose sugar
Contains Uracil (U) instead of
thymine
III. Proteins are made of many amino acids linked together.
IV. Proteins are made in ribosomes.
Types of RNA
Function
Messenger RNA
(mRNA)
Makes a copy of a section of DNA and brings it to
ribosome
Transfer RNA (tRNA)
Brings amino acids to the ribosome to form protein
Ribosomal RNA (rRNA) Makes of part of the ribosome
V. Steps of protein synthesis: (*fig 12-18)
A. Transcription – RNA makes a complementary copy of a section of
DNA and takes to ribosome
ex: DNA strand: A A T T G G C C C
RNA copy: U U A A C C G G G
a. DNA contains coding regions called exons and noncoding regions called introns (RNA only takes copy of exons to
ribosome)
B. Translation – tRNA read bases in mRNA and bring amino
acids to ribosome in correct sequence using the genetic code
Genetic Code: (fig 12-17)
-mRNA is read by tRNA 3 bases at a time.
-Each 3 base sequence is called a codon
-Each codon codes for a certain amino acid (there are 20 different
amino acids)
C. Protein assembly – the ribosome moves along the mRNA,
connecting new tRNA molecules and amino acids
Example of protein synthesis:
Strand of DNA:
TAC GCA
mRNA codon:
AUG CGU
tRNA anticodon:
UAC GCA
amino acids:
Met - Arg -
TGG
ACC
UGG
Thr -
AAT
UUA
A AU
Leu-
Section 12-4: Mutations
I. Mutation – A change in a gene. Mutations are a source of genetic
variation. Not all mutations are harmful!
A. Two types of mutations:
a. Point mutations – change in a single base (see fig 12-20)
1. Substitution – one base is substituted for another
Original Sequence:
DNA:
GCA TAT ATG
mRNA:
CGU AUA UAC
amino acid:
Arg- Iso- TyrAfter Substitution:
DNA:
GTA TAT ATG
mRNA:
CAU AUA UAC
amino acid:
Hist- Iso- Tyr2. Frameshift mutations: *harmful point
mutations because they change the “reading frame”
i.
insertion – an extra base in inserted
ii.
Substitution
deletion – a base is left out
Insertion
Deletion
b. Chromosomal mutations – change in a structure of
chromosome (see fig 12-21)