AP Biology Chapter 17 Study Guide

Gene Expression

DNA -> premRNA -> mRNA -> rRNA

-Process by which DNA directs protein synthesis

-Transcription of DNA -> mRNA

-Translation of mRNA -> rRNA

Archibald Garrod

-1902, suggested genes dictate phenotypes through enzymes that catalyze specific chemical reactions

-Symptoms of an inherited disease are due to an inability to synthesize a certain enzyme

Beadle and Tatum

-Used bread mold (Neurospora crassa) and X-rays to create mutants, 3 classes w/ mutations

-Class I: Gene A did not produce enzyme A

-Class II: Gene B did not produce enzyme B

-Class III: Gene C did not produce enzyme C

-One gene-one enzyme hypothesis

One Gene Hypothesis

-Not all proteins are enzymes

-Restated as one gene-one polypeptide hypothesis

RNA

Bridge between genes and proteins for which they code

-3 types

a) mRNA

b) tRNA

c) rRNA

Ribosomes

Site of translation

Prokaryotes

Translation of mRNA can begin before transcription is done

-Transcription -> Translation

-No nucleus

Eukaryotic Cell

Nuclear Envelope separates transcription from translation

-Contain a nucleus

-RNA processing occurs

-Transcription -> RNA processing -> Translation

Primary Transcript

Pre-mRNA

Central Dogma

Concept that cells are governed by a cellular chain of command:

DNA -> RNA -> Protein

Triplet Code

3 nucleotide words transcribed into mRNA and translated into amino acids (a protein)

DNA Template Strand

Is used for copying of the mRNA strand

-Also called the promoter

mRNA base triplets

Codons, code for amino acids

-5' -> 3'

-64 triplets, 3 code for stop

Reading Frame

Correct reading order of mRNA triplets

Amino Acid Code

Redundant, not ambiguous

Transcription

-DNA -> mRNA

-3 Steps

1) Inititation: RNA Polymerase + Promoter

2) Elongation: Runs down DNA

3) Termination: Termination signal

RNA Polymerase

Pries DNA apart and joins together RNA nucleotides

-No primer needed

Start point

Found on the promoter

-Signaled by promoter

Transcription Factors

Mediate binding of RNA polymerase and initiation of transcription

Inititation (Transcription)

-Eukaryotic promoter containing TATA box

-Transcription factors (proteins) bind to DNA

-RNA polymerase arrives and a transcription initiation complex forms

Elongation (Transcription)

-RNA polymerase moves along DNA, untwists double helix 10-20 bases at a time

-Progresses at rate of 40 nucleotides per second in eukaryotes

-3' end is where nucleotides are added to growing RNA

-Gene can be transcribed simultaneously by multiple RNA polymerases

Termination (Transcription)

-Bacteria: Polymerase stops transcrption at end of terminator, mRNA is translated with no further changes

-Eukaryotes: Termination signal ends it

RNA Processing

-Only in eukaryotes

-Enzymes in eukaryotic nucleus modify pre-mRNA

2 Steps:

1) Alteration: 5' cap & 3' Poly-A tail

2) Splicing: Splice introns and join exons

RNA Processing modifications

-5' cap & 3' poly-A tail

-Seem to facilitate export of mRNA to cytoplasm

-Protect mRNA from hydrolytic enzymes

-Help ribosomes attach to 5' end

Introns

Intervening sequences

-Noncoding regions of mRNA

-Spliced out

Exons

Expressed parts of mRNA

-Translated into amino acid sequences

RNA Splicing

Removes introns and joins exons

Spliceosomes

Variety of proteins & small nuclear ribonucleoproteins (snRNPs)

-Recognize splice sits

-RNAs of the spliceosome catalyze the splicing reaction

-Form hydrogen bonds with intron

-RNAs act as enzymes inside of spliceosome

Ribozymes

Catalytic RNA molecules functioning as enzymes

-Splice RNA

-Not all enzymes are proteins

-Rendered obosolete the belief that all biological catalysts were proteins

3 properties:

-Can form 3D structure due to its ability to base-pair w/ itself

-Bases in RNA contain functional groups that may participate in catalysis

-RNA can hydrogen-bond with other nucleic acid molecules

Alternative RNA splicing

-Some introns can be translated

-Genes can code +1 type of protein

-# of different proteins > # of genes

Domains

Regions of proteins

-Different exons code for different domains

-Exon shuffling can lead to evolution of new proteins

tRNA

-Transfer RNA

-Transfers amino acid to growing protein (polypeptide) in a ribosome

-Not all tRNA molecules are identical

-Contain anticodon on one end & specific amino acid on the other

-Single RNA strand; 80 nucleotides long, cloverleaf shape

Aminoacyl-tRNA Synthetase

Enzyme that binds amino acids to tRNA

-Uses ATP to covalently bond the 2 and releases aminoacyl tRNA

Wobble

Flexible pairing at 3rd base of codon

-Allows tRNAs to bind to more than one codon

Ribosome

-Facilitates specific coupling of tRNA anticodons with mRNA codons in protein synthesis