Transcript 1. Gene Mutations

DNA & Genes
Chapter 11
DNA, RNA, &
Protein Synthesis
I.
DNA Molecule of Heredity
A. Structure
• DNA (polymer) is a long molecule made up
of Nucleotides (monomers)
• A Nucleotide consists of:
– Deoxyribose (a 5-carbon sugar)
– a phosphate group
– One of 4 Nitrogenous bases (contain nitrogen)
• Adenine (A)
PURINES
• Guanine (G)
• Cytosine (C)
PYRIMIDINES
• Thymine (T)
•The nitrogenous bases of DNA (purines –
double ring / pyrimidines single ring)
Structure of DNA (cont.)
• DNA is like a twisted ladder:
– Rungs: complementary base pairs (A=T, G=C)
– Uprights: deoxyribose and phosphate groups
• Your Turn: Match this DNA base sequence with its correct
complementary DNA bases:
• T-C-G-A-A-C-T
• A-G-C-T-T-G-A
B. History
1. CHARGAFF (1949):
discovered that the % of
Cytosine and Guanine
were about the same in
DNA; the same was
true about Adenine and
Thymine
– This suggests BASE
PAIRING………..
that C bonds with G
and A bonds with T!
Source of
DNA
A
T
G
C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9
19.8
History (cont.)
2. Wilkins and
Franklin(1952): took
X-Ray photographs of DNA
which suggested a twisted,
helical structure, 2 strands, and
bases in the center
3. Watson and Crick
(1953): using all the research
to date, discovered the structure
for DNA: A DOUBLE HELIX
(with sugar-phosphate backbones
and bases on the inside held
together by H bonds)
C. DNA Replication:
making more DNA during the S Phase of the Cell Cycle
(in the nucleus)
1. The enzyme helicase unwinds DNA double helix
(breaks hydrogen bonds btwn. bases) & a
replication fork is created.
(Each old DNA strand will act as a template for 2
new strands to be added on)
2. Enzyme called DNA Polymerase binds to
replication fork and adds free nucleotides to each
old strand of DNA
3. DNA Polymerase remains attached until 2 new
DNA strands are created; it “proofreads” the
strands to minimize error in the process.
DNA Replication (cont.)
• Diagram of DNA Replication:
II.
DNA  Protein
RNA: Ribonucleic Acid
Used to make proteins
Single-stranded polymer made up of nucleotides.
RNA Monomer (Nucleotide) is made of Ribose (5 C sugar) + Phosphate group + N Base
Cytosine (C)
Guanine (G)
Adenine (A)
Uracil (U) – NO THYMINE in RNA!
Types of RNA
– 3 types of RNA:
1. messenger RNA (mRNA) – single stranded
transmits info from DNA to protein syn.
2. transfer RNA (tRNA) - single stranded/
20 or more varieties ea. w/ ability to bond to
only
1 specific AA
3. ribosomal RNA (rRNA) – globular / major
component of ribosome
Protein Synthesis (overview)
• 2 Stages in making proteins:
1) Transcription – using DNA template to
make mRNA strand
2) Translation – using mRNA strand to create
polypeptides
DNA
Transcription
RNA
Translation
Protein
1. Transcription
• The Goal of Transcription is to produce a singlestranded mRNA helix that contains information
from DNA to make proteins
• How it’s done: (This happens in the Nucleus!)
1. DNA strand unwinds/unzips complementary DNA strands
2. Enzyme called RNA Polymerase binds to DNA “promoter”
regions and “plugs in” complementary RNA nucleotides to the
DNA template.
– Example = DNA Template: ATTGGCAGT
new RNA Strand: UAACCGUCA
Transcription (cont.)
Transcription (cont.)
3. Once produced, this pre-mRNA
strand breaks away when RNA
polymerase reaches a sequence of
bases on DNA that act as a stop sign.
• The finished product (mRNA)
moves out of the Nucleus through a
nuclear pore into the cytoplasm.
4. 2 DNA complementary strands
rejoin
2. The Genetic Code
• How do we get proteins from mRNA
strands?
• The mRNA strand must be read in groups of
3 nucleotides, called a CODON.
• Different Codons translate for different
Amino acids.
Codons in mRNA
Codons in mRNA
• “Start” codon = AUG (Methionine)
• “Stop” codons = UAA, UAG, and UGA
• Example:
• mRNA Strand:
• U-C-A-U-G-G-G-C-A-C-A-U-G-C-U-U-U-U-G-A-G
methionine
glycine
threonine cysteine phenylalanine STOP
3. Translation
• The Goal of Translation is to “translate” these
mRNA codons into their amino acids to form a
polypeptide.
• How it’s done:
1. mRNA strand attaches to a ribosome (rRNA)
2. Each mRNA codon passes through ribosome
3. Free-floating Amino Acids from cytosol are brought to
ribosome by tRNA
4. Each tRNA has an anticodon to match up to mRNA
codons
5. Amino Acids are joined as tRNA keeps bringing them
6. Polypeptide chain grows until “stop” codon is reached
Translation (cont.)
• Translation
III. Genetic Changes: Mutations
A. Types of Mutations
1. Gene Mutations: changes in nucleotides
– Point Mutations or Frameshift Mutations
2. Chromosome Mutations: changes in # or
structure of chromosome
–
–
–
–
Deletion
Insertion/Duplication
Inversion
Translocation
1. Gene Mutations
a. Point Mutation: the
substitution, addition or
removal of a single
nucleotide
b. Frameshift Mutations:
types of point mutations
that shift the “reading
frame” of the genetic
message
B. Chromosome Mutations
1. Deletion……………………………
2. Insertion/Duplication…………
3. Inversion…………………………
4. Translocation…………………….
Reproductive vs. Body Cell
Mutations
• Reproductive Cells – Mutations when
multiplied become the genetic makeup of the
new offspring.
• Body Cells – Ultraviolet Radiation, affects
the cell of the individual. Not passed on, but
can cause harm to individual. (Mutagens)
Are all mutations bad?
• No!
• Positive Mutations are often called
adaptations.
• These adaptations are beneficial to the
species if they become a predominant part
of the gene pool.
Homework
• In your book page. 306 Mini-Lab 11-2
• Complete the procedure and answer
questions 1-3.
Quiz Thursday on DNA, Replication, Protein
Synthesis, and Mutations
Gene Regulation in Prokaryotes
The lac operon enables the production of lactose-processing enzymes in E.
coli, but only when needed.
• In the presence of lactose, the
• In the absence of lactose, the
repressor is inhibited from
repressor protein binds to the
binding with the operator; this
operator on DNA and inhibits
all ows transcription to take
transcription of lactoseplace to produce lactoseprocessing enzymes.
processing enzymes.