dna makes rna the central dogma makes...

The Central Dogma• DNA makes RNA makes Proteins

TRANSCRIPTION

RNA PROCESSING

RNA transcript5ʹ

Exon

NUCLEUS

FORMATION OF INITIATION COMPLEX

CYTOPLASM

3ʹ

DNA

RNA polymerase

RNA transcript (pre-mRNA)

Intron

Aminoacyl-tRNA synthetase

Amino acid

tRNAAMINO ACID ACTIVATION

3ʹ

mRNA

A

P

E Ribosomal subunits

5ʹ

Growing polypeptide

E A

Activated amino acid

Anticodon

TRANSLATION

Codon

Ribosome

The Central Dogma

• DNA makes RNA makes Proteins

Transcription• DNA --> RNA• requires RNA polymerase enzyme

• three types (in Euk) [IB: you don’t need to know the differences]• RNAp II

• makes mRNA• RNAp extends new RNA in 5’-3’

• (other RNA types in mito, chloro)• reads template strand DNA 3’ -> 5’• adds nucleotides to the 3’ end of growing RNA

• Initiation, Elongation, Termination...

Transcription

• Initiation• In euk, initiation factors mediate RNAp binding• after RNAp binds:

• “transcription initiation complex”• How does the RNAp know which strand to copy?

• RNAp attaches to a promoter region• Elongation

• dbl helix re-bonds upstream of RNAp• multiple RNAp mols can operate on same gene at same time

• Termination• RNAp stops at end of terminator

Topic 7.2: Transcription and Gene Expression

• Understandings (overview)

1.Transcription occurs in a 5’ to 3’ direction2.Nucleosomes help to regulate transcription in eukaryotes3.Eukaryotic cells modify mRNA after transcription4.Splicing of mRNA increases the number of different proteins an

organism can produce5.Gene expression is regulated by proteins that bind to specific base

sequences in DNA6.The environment of a cell and of an organism has an impact on

gene expression

Topic 7.2: Transcription and Gene Expression• Understandings:

1.Transcription occurs in a 5’ to 3’ direction• nucleoside triphosphates (NTPs) line up opposite their

complementary base partner• RNA polymerase covalently binds the NTPs (releasing the two

additional P)• The 5’-phosphate links to the 3’-end of the growing mRNA

strand• THUS: transcription occurs in a 5’ → 3’ direction


2.Nucleosomes help to regulate transcription in eukaryotes• media: “Inheritance”, pt 1 & 2 (Radiolab)

Methylation Acetylation

• Adding an acetyl group to the tail neutralizes charge = DNA less tightly coiled and increasing transcription

• Adding a methyl group to the tail maintains positive charge = DNA more coiled and reducing transcription

http://www.radiolab.org/story/251876-inheritance/

Topic 7.2: Transcription and Gene Expression• Understandings: 3.Eukaryotic cells modify mRNA after transcription

• Three processes:• Capping

• methyl group added to the 5’-end• protection against exonucleases• ribosome attachment

• Poly-A tail• long chain of adenine nucleotides to the 3’-end• helps export from the nucleus

• splicing• introns removed (“intervening introns”)• exons fused (“expressed exons")


4.Splicing of mRNA increases the number of different proteins an organism can produce

Topic 7.2: Transcription and Gene Expression• Understandings: 5.Gene expression is regulated by proteins that bind to specific base

sequences in DNA• Activator proteins bind to enhancer sites• Repressor proteins bind to silencer sites


6.The environment of a cell and of an organism has an impact on gene expression

Topic 7.2: Transcription and Gene ExpressionTypes of Chromatin:

Some DNA = permanently supercoiled, some changes over the life cycle of the cell


6.The environment of a cell and of an organism has an impact on gene expression

Topic 7.2: Transcription and Gene Expression• Skill:

• Analyze changes in methylation pattern

LE 17-7b

Elongation Non-template strand of DNA

RNA polymerase

RNA nucleotides

3ʹ end3ʹ

5ʹ

5ʹ

Newly made RNA

Template strand of DNA

Direction of transcription (“downstream”)

LE 17-7a-1

Promoter Transcription unit

RNA polymeraseStart point DNA

5ʹ3ʹ

3ʹ5ʹ

LE 17-7a-2

Promoter

5ʹ3ʹ

3ʹ5ʹ

3ʹ5ʹ

5ʹ3ʹ

Transcription unit

DNA

Initiation

Start pointRNA polymerase

Unwound DNA

RNA transcript


LE 17-7a-3Promoter

5ʹ3ʹ

Transcription unit

3ʹ5DNAStart point

RNA polymeraseInitiation

3ʹ5

5ʹ3ʹ

Unwound DNA

RNA transcript


Elongation

Rewound DNA

3ʹ5

5ʹ3ʹ 3ʹ

5ʹ

RNA transcript

LE 17-7a-4Promoter

3ʹ5

Transcription unit

DNA

InitiationRNA polymerase

Start point


RNA transcript

Unwound DNA

Elongation

3ʹ

3ʹ

5ʹ3

5ʹ

5ʹ

3ʹ 5ʹ

Rewound DNA

5ʹ 3ʹ

3ʹ5ʹ 3ʹ5ʹ

RNA transcript Termination

3ʹ5ʹ

5ʹ 3ʹCompleted RNA transcript

RNA editing• in prok:

• transcript is translated directly (except tRNA, rRNA)• in euk: modifications in nucleus

• 5’ cap added (modified G)• 3’ end gets poly-A-tail

• 50-250 A-nucleotides

RNA editing, cont’d• in cytoplasm: RNA splicing• avg transcript = 10,000bp. Avg prot

= 400aa. (8800bp cut!)• introns cut out, exons joined

• cut & splice by: spliceosome• = prot + small nuclear

ribonucleoproteins (snRNPs)• (“snurps”)

• Why are introns a good thing?• alternative splicing• regulatory introns (miRNA)

5ʹExon 1 Intron Exon 2


Other proteins

Protein

snRNA

snRNPs

Spliceosome

5ʹ

Spliceosome components

Cut-out intron

mRNA

Exon 1 Exon 25ʹ

LE 17-12

Gene

Transcription

RNA processing

Translation

Domain 2

Domain 3

Domain 1

Polypeptide

Exon 1 Intron Exon 2 Intron Exon 3

DNA

Translation

• tRNA is the translator• process mediated by ribosome

• large, small subunits• proteins + rRNA (most abundant RNA)

• tRNA deposits a.a., codon by codon• ribosome joins a.a.’s into polypeptide

• 45 different tRNA’s; why not 64?• wobble• third base in codon doesn’t have to match

• ex: U match with A or G• thus: more than one codon can code for same a.a

• ex: ACA, ACU, ACC, ACG all code for Thr

Ribosomes

• during initiation:• start codon attracts initiator tRNA w/ Met• sm subunit attaches to mRNA• sm subunit moves downstream• lg subunit attaches

• three sites:• A: holds tRNA w/ next a.a for growing chain• P: hold tRNA carrying the growing chain• E: ejection seat for tRNA

• ribosome = big ribozyme• hydrolysis of GTP supplies E• continues until stop codon reached

Translate this:• AUG,GAG,GAA,AUA,GAU,UGA

• AUG,GUG,GAA,AUA,GAU,UGA

• AUG,GGG,AAA,UAG,AUU,GA

• AUG,GCA,GGA,AAU,AGA,UUG,A

TRANSCRIPTION

RNA PROCESSING

RNA transcript5ʹ

Exon

NUCLEUS

FORMATION OF INITIATION COMPLEX

CYTOPLASM

3ʹ

DNA

RNA polymerase


Intron

Aminoacyl-tRNA synthetase

Amino acid

tRNAAMINO ACID ACTIVATION

3ʹ

mRNA

A

P

E Ribosomal subunits

5ʹ

Growing polypeptide

E A

Activated amino acid

Anticodon

TRANSLATION

Codon

Ribosome

Ribozymes

• RNA: more than DNA message• H-bond to other nucleic acids• form 3-D structure by self-bonding• contains functional catalytic groups

• Ribozymes: • def = RNA molecules catalyzing a

chem rxn• ribozymes catalyze their own cleavage,

and even their own synthesis• RNA can store, transmit, and duplicate

genetic info• also regulate gene expression

• snRNA, siRNA, miRNA• RNA nucleotides have been made

spontaneously in lab• Key to origin of life?

The End

DNA Review

DNA/RNA Review• Scientists• DNA structure• bases• nucleotides• diagram DNA• replication = semi-conservative• RNA vs DNA• RNA functions (r,t,m)• transcription

• sense strand • regulation of transcription

• promoter causes RNA polymerase to bind• prokaryotes: introns

• introns/exons• reverse transcriptase (Ch 18; HIV, cDNA & mol bio)

• translation• initiation, elongation, termination

dna makes rna the central dogma makes...

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