Download Genes and Heredity Nucleotide Structure A G C T A C DNA

Nucleotide Structure
Genes and Heredity
O
Gene = Short segment of a chromosome
(usually hundreds to many
thousands of nucleotides long) that
encodes amino acid sequence of a
functional product (an RNA or
protein)
H
HO P O
O C5’ H
H
HO
Phosphate
HO H
Deoxyribose
P
A
3’
Chromosome
Free
3’
5’
5’
3’
T
5’
3’
G
C
A DNA molecule is made up of two
strands. These strands are antiparallel (they run in opposite
directions). The sequence of one
strand is complementary to the
sequence of the other strand
(A pairs with T; G pairs with C).
5’
3’
T
A
P
P
5’
3’
T
A
RNA primers create short
(a few nucleotides)
double-stranded regions
to which DNA
Polymerase can bind.
3’
5’
C
3’
G
P
3’
P
Cytosine
DNA Helicase unwinds the
double strand to begin the
process of DNA Replication
Leading Strand
P
P
Guanine
Lagging Strand
P
P
5’
3’
DNA Replication
A strand of DNA is a string of
nucleotides hooked together by sugarphosphate bonds.
P
A
Thymine
C
5’
3’
5’
G
Attached
DNA Structure
P
P
T
Adenine
3’
5’
P
Phenotype = type of proteins an
organism produces AND the
observable characteristics that
result from these proteins
P
Genotype = type of gene(s) an
individual possesses
One molecule
of DNA
Nitrogenous
NitrogenousBase
Base
O
4’ C
C
C1’
HH
H C
C
C2’ H
3’ C
5’
DNA Polymerase reads old DNA
strand (3 ’!5 ’) and synthesizes a
complementary strand.
5’
Bacterial DNA Replication (Rolling Circle Model)
DNA Replication (continued)
After completion of initial DNA synthesis,
two “identical ” DNA molecules result
(here shown as blue and red).
DNA
Ligase
DNA Helicase
DNA Polymerase returns and replaces
the RNA primers with DNA.
The new strand of
one molecule has
identical sequence to
the old strand of the
other molecule.
DNA
Ligase
Old Strand
New Strand
The enzyme, DNA Ligase , glues
together the sugar-phosphate
backbones of DNA fragments.
New Strand
Old Strand
DNA Polymerase reads old DNA
strand (3 ’!5 ’) and synthesizes a
complementary strand.
Transcription
DNA
RNA
Similar to DNA Replication except: (1) RNA
Polymerase synthesizes RNA and (2) RNA is
produced (not DNA).
O
H
HO P O C H
HO
Phosphate
O
C HH C
H C C H
U Nitrogenous Base
Characteristic
Name
Size
Function
Structure
Number of different types
HO OH
H
Deoxyribose
Ribose
Characteristic
Sugar
Nucleotides
Complementary Base Pairing
Structure of DNA strands
Types of RNA
Information Storage
DNA
Deoxyribose (2’ carbon has Hydrogen)
A, G, C, Thymine (T)
G:::C, A::T
Sugar-Phosphate Backbone presenting
nucleotides in sequence
Nucleotide sequence read 5’! 3’
RNA
Ribose (2’ carbon has hydroxyl -OH)
A, G, C, Uracil (U)
G:::C, A::U
Sugar-Phosphate Backbone presenting
nucleotides in sequence
Nucleotide sequence read 5’! 3’
Number of strands in typical molecule
Stability
Double-stranded
Very Stable (long-lasting)
Single-stranded
Somewhat unstable (short-term)
mRNA
Messenger RNA
Variable
Encodes amino acid
sequence of specific protein
Single-stranded, linear
tRNA
Transfer RNA
Short (~75 nucleotides)
Decodes mRNA sequence,
carries a specific amino acid
Single-stranded but twisted
into characteristic clover-leaf
shape
As many as there are
proteins to be made (~5000
in E. coli; ~100,000 in
humans)
20 to 64
rRNA
Ribosomal RNA
3 different sizes
Forms functional part of
ribosome
Single-stranded but
packaged together with other
rRNAs and with ribosomal
proteins
3
AA
Anticodon
tRNA
Ribosome
Translation
1. Small ribosomal subunit
binds to mRNA and moves 5 ’ !
3’ until it reaches a START
CODON.
The Universal Genetic Code
3. Large ribosomal subunit
binds such that tRNA -Met fits
into one the two pockets.
5’G C G A C U U G A U G C C C U U U U C A U G A 3’
mRNA
2. tRNA binds to start codon .
This tRNA has ANTICODON
with complementary sequence
to start codon . This tRNA also
carries the specific amino acid
Methionine .
Pro
5. The amino acids bind to one
another. The first tRNA , without
its amino acid, becomes
destabilized and falls out of the
ribosome. The ribosome then
moves down one codon .
Met
4. A second tRNA , whose
anticodon is complementary to
the exposed codon , fits into the
second pocket of the large
ribosomal subunit.
Prokaryotes vs Eukaryotes: Chromosome Structure
Characteristic
Prokaryotes
Number of Chromosomes
Chromosome Shape
Plasmids
Direction of Replication
Introns
Gene Arrangement
RNA Editing
Timing of
Transcrption /Translation
Eukaryotes
Prokaryotic Gene Expression
Plasmid
Small, circular
molecule of DNA.
May contain useful
genes such as those
for antibiotic
resistance,
bacteriocins ,and
genes that cause
increased genetic
recombination.
Chromosome
One. Circular. No
histones . Contains
all genes essential
for fundamental
processes
5’!3 ’, bidirectional
RNA Polymerase binds to
operator, reads the DNA and
transcribes the structural
genes (Z, Y, and A).
I gene
Typical Procaryotic Cell
lac Operon
Promotor
Operator
(RNA
(Repressor
Polymerase binding site)
binding site)
Lactose
Repressor Protein
Z
Y
A
Mutations: Genotypic Effects
DNA
5’C
G G T A C G G A C C C A C G T C G A C T T T T T A
3’G C C A T G C C T G G G T G C A G C T G A A A A A T
Mutations: Phenotypic Effects
3’
5’C
G G T A C G G A C C C A C G T C G A C T T T T T A
3’G C C A T G C C T G G G T G C A G C T G A A A A A T
5’
mRNA
What is the nucleotide sequence of the other DNA strand?
1. Amino Acid Sequence?
What is a mutation?
2. If nucleotide 12 mutates from C to T what is the amino acid sequence?
What is a BASE SUBSTITUTUION mutation ?
What is a DELETION mutation?
3. If nucleotide 11 mutates from C to T, what is the amino acid sequence?
What is a ADDITION mutation ?
4. If nucleotides 14 and 15 are deleted, what is the amino acid sequence?
3’
5’