Download DNA RNA

UNIT 1 INFORMATION METHODS OF A CELL
What do you know about DNA?
• Building blocks are called?
– nucleotides
• The shape is ?
– Double helix
• The three primary components of a nucleotide are?
– Sugar, phosphate, nitrogen base
• Where are each of these found?
– The sugar and phosphate are in the backbone; the
nitrogen base is on the rungs between DNA strands
• The sugar is?
– deoxyribose
DNA RNA
DNA Backbone Structure
• Alternate phosphate and sugar (deoxyribose), phosphate ester bonds
DNA Backbone Structure
• Alternate phosphate and sugar (deoxyribose), phosphate ester bonds
DNA RNA
DNA RNA
DNA Primary Structure Summary
• Backbone (sugar+phophate with phosphate ester
bonds and base side chains)
DNA RNA
What are the base pairing rules
for DNA?
DNA Double Helix
• Base pairing by unique hydrogen bonds
• C - G and A - T pairs
DNA Double Helix
• Base pairing by unique hydrogen bonds
• C - G and A - T pairs
• Each strand of the
double helix is
oriented in the
opposite direction
5 end
3 end
P
P
P
P
P
• What is this
arrangement called?
P
P
• “Antiparallel “
P
Figure 10.5B
3 end
5 end
What process is used
in the cell to make new
strands of DNA?
DNA Replication
DNA
What do you remember?
• What does semi conservative replication
mean?
– The resulting DNA includes one original strand
and one new strand
– One original strand is “conserved” or saved.
Untwisting and replication of DNA
• each strand is a template for a new strand
helicase
DNA polymerase
Figure 10.4B
What is the job of the helicase enzyme?
– To unzip the DNA
What is the job of the DNA polymerases?
– To build new DNA strands by attaching
nucleotides to the parent strand
What is the job of ligase?
– To attach fragments of DNA together
DNA Replication
• Complementary base pairs form new strands.
• DNA
polymerase
works in
only one
direction
• Telomere
sequences
are lost
with each
replication.
• Cancer,
aging
DNA polymerase
molecule
5 end
Daughter strand
synthesized
continuously
Parental DNA
5
3
Daughter
strand
synthesized
in pieces
3
5
P
5
3
3
5
P
telomeres
DNA ligase
Overall direction of replication
Figure 10.5C
So what is a telomere anyway?
• A telomere is a repeating DNA sequence (for example,
TTAGGG) at the end of the body's chromosomes.
• The telomere can reach a length of 15,000 base pairs.
• Telomeres function by preventing chromosomes from
losing base pair sequences at their ends. They also stop
chromosomes from fusing to each other.
• Each time a cell divides, some of the telomere is lost
(usually 25-200 base pairs per division).
• When the telomere becomes too short, the chromosome
reaches a "critical length" and can no longer replicate.
• This means that a cell becomes "old" and dies by a process
called apoptosis.
So what do telomeres have to do
with Cancer?
• Its all about the enzyme, telomerase.
• Telomerase causes the continued addition of DNA
ends (telomeres) so cells with active production of
telomerase continue to grow and divide. Body
cells no longer produce telemerase.
• What kind of cells keep growing and dividing?
• Fetal cells, tumor cells including cancer cells
How can entire chromosomes be replicated during S phase
of the cell cycle?
• DNA replication begins at many specific sites
Origin of replication
Parental strand
Daughter strand
Bubble
Two daughter DNA molecules
What are these sites called?
Replication Bubbles
Figure 10.5A
DNA
DNA
RNA polymerase
• In transcription,
DNA helix unzips
– RNA nucleotides line
up along one strand
of DNA, following the
base-pairing rules
– single-stranded
messenger RNA peels
away and DNA
strands rejoin
– What are the 3 steps
of transcription? Figure 10.9B
DNA of gene
Promoter
DNA
Initiation
Elongation
Terminator
DNA
Area shown
in Figure 10.9A
Termination
Growing
RNA
Completed RNA
RNA
polymerase
DNA
RNA Transcription
• In nucleus, DNA guides the synthesis of mRNA
RNA Transcription
• RNA polymerase and elongation reaction
RNA Transcription
• RNA polymerase and elongation reaction
Eukaryotic RNA is processed before leaving the nucleus
• Noncoding
segments,
introns, are
spliced out
• A cap and a tail
are added to the
ends
Exon Intron
Exon
Intron
Exon
DNA
Cap
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
NUCLEUS
CYTOPLASM
Figure 10.10
RNA vs. DNA
• RNA contains Uracil, not Thymine
• Sugar is Ribose
• Usually single stranded
Phosphate
group
Sugar
(ribose)
Nitrogenous base
(A, G, C, or U)
Types of RNA
• mRNA contains codons which code for amino acids.
DNA
Types of RNA
• rRNA - Ribosome - contains enzymes and keeps
everything together
Types of RNA
• tRNA - Transfer RNA carries amino acid and read
codons on m-RNA through its own anticodons.
Types of RNA
• tRNA - Transfer RNA carries amino acid and read
codons on m-RNA through its own anticodons.
Protein Synthesis
Protein Synthesis
Protein Synthesis
Protein Synthesis
Protein Synthesis
Check
• The following section of DNA is used to
build a strand of mRNA
• 3’ – GAA- CCC- TTT- 5’
• What is the corresponding mRNA
sequesnce?
• What are the anticodons on the tRNA in the
next step?
Modified from www.elmhurst.edu/~chm/onlcourse/CHM103/Rx22DNA.ppt
• Summary of
transcription
and translation
TRANSCRIPTION
DNA
mRNA
RNA
polymerase
Stage 1 mRNA is
transcribed from a
DNA template.
Amino acid
TRANSLATION
Enzyme
Stage 2 Each amino
acid attaches to its
proper tRNA with the
help of a specific
enzyme and ATP.
tRNA
Initiator
tRNA
mRNA
Figure 10.15
Anticodon
Large
ribosomal
subunit
Start
Codon
Small
ribosomal
subunit
Stage 3 Initiation of
polypeptide synthesis
The mRNA, the first
tRNA, and the
ribosomal subunits
come together.
New
peptide
bond
forming
Growing
polypeptide
Codons
Stage 4 Elongation
A succession of tRNAs
add their amino acids to
the polypeptide chain as
the mRNA is moved
through the ribosome,
one codon at a time.
mRNA
Polypeptide
Stop Codon
Figure 10.15 (continued)
Stage 5 Termination
The ribosome recognizes
a stop codon. The polypeptide is terminated and
released.