AP Biology Nucleic Acids Examples: RNA (ribonucleic acid) single helix DNA (deoxyribonucleic...

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AP Biology Nucleic Acids Examples: RNA (ribonucleic acid) single helix DNA (deoxyribonucleic acid) double helix Structure: monomers = nucleotides RN A DN A

Transcript of AP Biology Nucleic Acids Examples: RNA (ribonucleic acid) single helix DNA (deoxyribonucleic...

AP Biology

Nucleic Acids Examples:

RNA (ribonucleic acid) single helix

DNA (deoxyribonucleic acid) double helix

Structure: monomers = nucleotides

RNA

DNA

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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!

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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!

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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?

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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?

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DNA molecule Double helix

H bonds between bases join the 2 strands A :: T C :: G

H bonds?Why is this important?

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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?

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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 2007-2008

From Gene to Protein

How Genes Work

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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!

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Transcription

fromDNA nucleic acid language

toRNA nucleic acid language

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RNA ribose sugar N-bases

uracil instead of thymine U : A C : G

single stranded lots of RNAs

mRNA, tRNA, rRNA, siRNA…

RNADNAtranscription

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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

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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

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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'

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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!

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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

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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 2007-2008

Translation

fromnucleic acid language

toamino acid language

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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

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AUGCGUGUAAAUGCAUGCGCC

mRNA

mRNA codes for proteins in triplets

TACGCACATTTACGTACGCGG

DNA

AUGCGUGUAAAUGCAUGCGCC

mRNA

Met Arg Val Asn Ala Cys

Alaprotein

?

codon

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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

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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?

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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!

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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!

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Transcription & translation are simultaneous in bacteria DNA is in

cytoplasm no mRNA

editing ribosomes

read mRNA as it is being transcribed

Translation in Prokaryotes

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Translation: prokaryotes vs. eukaryotes Differences between prokaryotes &

eukaryotes time & physical separation between

processes takes eukaryote ~1 hour

from DNA to protein no RNA processing