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AP Biology
Nucleic Acids Examples:
RNA (ribonucleic acid) single helix
DNA (deoxyribonucleic acid) double helix
Structure: monomers = nucleotides
RNA
DNA
AP Biology
Nucleotides 3 parts
nitrogen base (C-N ring) pentose sugar (5C)
ribose in RNA deoxyribose in DNA
phosphate (PO4) group
Are nucleic acidscharged molecules?
Nitrogen baseI’m the
A,T,C,G or Upart!
AP Biology
Types of nucleotides 2 types of nucleotides
different nitrogen bases purines
double ring N base adenine (A) guanine (G)
pyrimidines single ring N base cytosine (C) thymine (T) uracil (U)
Purine = AGPure silver!
AP Biology
Nucleic polymer Backbone
sugar to PO4 bond phosphodiester bond
new base added to sugar of previous base
polymer grows in one direction N bases hang off the
sugar-phosphate backbone
Dangling bases?Why is this important?
AP Biology
Pairing of nucleotides Nucleotides bond between
DNA strands H bonds purine :: pyrimidine A :: T
2 H bonds G :: C
3 H bonds
Matching bases?Why is this important?
AP Biology
DNA molecule Double helix
H bonds between bases join the 2 strands A :: T C :: G
H bonds?Why is this important?
AP Biology
Copying DNA Replication
2 strands of DNA helix are complementary have one, can build other have one, can rebuild the
whole
Matching halves?Why is this
a good system?
AP Biology
Interesting note… Ratio of A-T::G-C
affects stability of DNA molecule 2 H bonds vs. 3 H bonds biotech procedures
more G-C = need higher T° to separate strands
high T° organisms many G-C
parasites many A-T (don’t know why)
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
DNA gets all the glory,
but proteins do all the work!
AP Biology
RNA ribose sugar N-bases
uracil instead of thymine U : A C : G
single stranded lots of RNAs
mRNA, tRNA, rRNA, siRNA…
RNADNAtranscription
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
GG
G
G G
G G
G
G
GAA
AA A
A
A
A
A
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
RNA polymerases 3 RNA polymerase enzymes
RNA polymerase 1 only transcribes rRNA genes makes ribosomes
RNA polymerase 2 transcribes genes into mRNA
RNA polymerase 3 only transcribes tRNA genes
each has a specific promoter sequence it recognizes
AP Biology
Matching bases of DNA & RNA Match RNA bases to DNA
bases on one of the DNA strands
U
A G GGGGGT T A C A C T T T T TC C C CA A
U
UU
U
U
G
G
A
A
A C CRNA
polymerase
C
C
C
C
C
G
G
G
G
A
A
A
AA
5' 3'
AP Biology
Eukaryotic genes have junk! Eukaryotic genes are not continuous
exons = the real gene expressed / coding DNA
introns = the junk inbetween sequence
eukaryotic DNA
exon = coding (expressed) sequence
intron = noncoding (inbetween) sequence
intronscome out!
AP Biology
mRNA splicing
eukaryotic DNA
exon = coding (expressed) sequence
intron = noncoding (inbetween) sequence
primary mRNA
transcript
mature mRNAtranscript
pre-mRNA
spliced mRNA
Post-transcriptional processing eukaryotic mRNA needs work after transcription primary transcript = pre-mRNA mRNA splicing
edit out introns make mature mRNA transcript
~10,000 bases
~1,000 bases
AP Biology
Splicing must be accurate No room for mistakes!
a single base added or lost throws off the reading frame
AUG|CGG|UCC|GAU|AAG|GGC|CAU
AUGCGGCTATGGGUCCGAUAAGGGCCAUAUGCGGUCCGAUAAGGGCCAU
AUG|CGG|GUC|CGA|UAA|GGG|CCA|U
AUGCGGCTATGGGUCCGAUAAGGGCCAUAUGCGGGUCCGAUAAGGGCCAU
Met|Arg|Ser|Asp|Lys|Gly|His
Met|Arg|Val|Arg|STOP|
AP Biology
How does mRNA code for proteins?TACGCACATTTACGTACGCGG
DNA
AUGCGUGUAAAUGCAUGCGCC
mRNA
Met Arg Val Asn Ala Cys
Alaprotein
?
How can you code for 20 amino acids with only 4 nucleotide bases (A,U,G,C)?
4
4
20
ATCG
AUCG
AP Biology
AUGCGUGUAAAUGCAUGCGCC
mRNA
mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGG
DNA
AUGCGUGUAAAUGCAUGCGCC
mRNA
Met Arg Val Asn Ala Cys
Alaprotein
?
codon
AP Biology
Cracking the code1960 | 1968
Crick determined 3-letter (triplet) codon system
Nirenberg & Khorana
WHYDIDTHEREDBATEATTHEFATRATWHYDIDTHEREDBATEATTHEFATRAT
Nirenberg (47) & Khorana (17) determined mRNA–amino acid match added fabricated mRNA to test tube of
ribosomes, tRNA & amino acids created artificial UUUUU… mRNA found that UUU coded for phenylalanine
AP Biology
The code Code for ALL life!
strongest support for a common origin for all life
Code is redundant several codons for
each amino acid 3rd base “wobble”
Start codon AUG methionine
Stop codons UGA, UAA, UAG
Why is thewobble good?
AP Biology
How are the codons matched to amino acids?
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNA
aminoacid
tRNA anti-codon
codon
5 3
3 5
3 5
UAC
MetGCA
ArgCAU
Val
AP Biology 2007-2008
Protein Synthesis in Prokaryotes
Bacterial chromosome
mRNA
Cell wall
Cellmembrane
Transcription
Psssst…no nucleus!
AP Biology
Prokaryote vs. Eukaryote genes Prokaryotes
DNA in cytoplasm
circular chromosome
naked DNA
no introns
Eukaryotes DNA in nucleus linear
chromosomes DNA wound on
histone proteins introns vs.
exons
eukaryoticDNA
exon = coding (expressed) sequence
intron = noncoding (inbetween) sequence
intronscome out!
AP Biology
Transcription & translation are simultaneous in bacteria DNA is in
cytoplasm no mRNA
editing ribosomes
read mRNA as it is being transcribed
Translation in Prokaryotes