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Molecular Genetics ( from DNA to Trait ). Double helix structure of DNA. “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” Watson & Crick. Directionality of DNA. nucleotide. - PowerPoint PPT Presentation
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AP Biology
Double helix structure of DNA
“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” Watson & Crick
AP Biology
Directionality of DNA You need to
number the carbons! it matters!
OH
CH2O
4
5
3 2
1
PO4
N base
ribose
nucleotide
This will beIMPORTANT!!
AP Biology
Anti-parallel strands Nucleotides in DNA
backbone are bonded from phosphate to sugar between 3 & 5 carbons DNA molecule has
“direction” complementary strand runs
in opposite direction
3
5
5
3
AP Biology
Base pairing in DNA Purines
adenine (A) guanine (G)
Pyrimidines thymine (T) cytosine (C)
Pairing A : T
2 bonds C : G
3 bonds
AP Biology
Copying DNA Replication of DNA
base pairing allows each strand to serve as a template for a new strand
new strand is 1/2 parent template & 1/2 new DNA
AP Biology
Replication: 1st step Unwind DNA
helicase enzyme unwinds part of DNA helix stabilized by single-stranded binding proteins
single-stranded binding proteins replication fork
helicase
AP Biology
DNAPolymerase III
Replication: 2nd step
But…We’re missing
something!What?
Where’s theENERGY
for the bonding!
Build daughter DNA strand add new
complementary bases DNA polymerase III
AP Biology
Adding bases can only add
nucleotides to 3 end of a growing DNA strand need a “starter”
nucleotide to bond to
strand only grows 53
DNAPolymerase III
DNAPolymerase III
DNAPolymerase III
DNAPolymerase III
energy
energy
energy
Replication energy
3
3
5B.Y.O. ENERGY!
The energy rulesthe process
5
AP Biology
Editing & proofreading DNA 1000 bases/second =
lots of typos! DNA polymerase I
proofreads & corrects typos
repairs mismatched bases removes abnormal bases
repairs damage throughout life
reduces error rate from 1 in 10,000 to 1 in 100 million bases
AP Biology
Fast & accurate! It takes E. coli <1 hour to copy
5 million base pairs in its single chromosome divide to form 2 identical daughter cells
Human cell copies its 6 billion bases & divide into daughter cells in only few hours remarkably accurate only ~1 error per 100 million bases ~30 errors per cell cycle
AP Biology
The “Central Dogma” Flow of genetic information in a cell
How do we move information from DNA to proteins?
transcriptiontranslation
replication
protein
RNA
DNA
trait
AP Biology
RNA
ribose sugar N-bases
uracil instead of thymine U : A C : G
single stranded
AP Biology
There are Different RNAs with Distinct Functions
AP Biology 2007-2008
Transcription makes an RNA copy of DNA
fromDNA nucleic acid language
toRNA nucleic acid language
AP Biology
Transcription
RNA polymerase acts here
The enzyme RNA polymerase opens the DNA strands and synthesizes an RNA complementary to only one of the DNA strands.
AP Biology
Transcription Making mRNA
transcribed DNA strand = template strand untranscribed DNA strand = coding strand
same sequence as RNA synthesis of complementary RNA strand
transcription bubble enzyme
RNA polymerase
template strand
rewinding
mRNA RNA polymerase
unwinding
coding strand
DNAC C C
C
C
C
C
C
C CC
G
G G G
G G
G G
G
G
GAA
AA A
A
A
AA
A A
A
AT
T T
T
T
T
T
T
T T
T
T
U U
5
35
3
3
5build RNA 53
AP Biology
Eukaryotic Genes are Segmented link
Genes are made of parts represented in the mRNA (exons) and parts that are transcribed but not present in the mRNA (introns).
Introns are removed from the primary transcript and exons are spliced together to make mRNA.
In some genes more than 90% of the pre-mRNA is destroyed, never to appear in the mRNA.
AP Biology 2007-2008
Translation in Eukaryotes
AP Biology
Triplet Code Codons
blocks of 3 nucleotides decoded into the sequence of amino acids
AP Biology
DNA code mRNA (copied code) gives amino acid sequence tRNA gets amino acids ribosomes assembles polypeptide chains make up proteins…
AP Biology
The Cryptogram of LIFE
These are the words of the genetic language.
AP Biology
tRNA An adaptor Couples
codons and anticodons
Amino Acids in proper order as per DNA
AP Biology
E P A
AP Biology
Can you tell the story?
Review
DNA
pre-mRNA
ribosome
tRNA
aminoacids
polypeptide
mature mRNA
5' cap
polyA tail
large ribosomal subunit
small ribosomal subunit
aminoacyl tRNAsynthetase
E P A
5'
3'
RNA polymerase
exon introntRNA