DNA and RNA II Sapling Chapter 6 short version You are responsible for textbook material covered by the worksheets. CP Biology Paul VI Catholic High School

DNA and RNA CENTRAL DOGMA DNA RNA PROTEIN (Francis Crick 1956)

DNA and RNA Information flows from the nucleus to the cytoplasm

DNA and RNA DNA TRANSCRIPTION Information storage RNA Information Carrier PROTEIN TRANSLATION Active Cell Machinery

DNA and RNA GENETIC CODE: Information for expressed traits contained in the nucleotide sequence of DNA. CODONS: Sequence of 3 nucleotides specifying a particular amino acid. (Brenner & Crick 1961)

DNA and RNA THE GENETIC CODE CONSISTS OF GROUPS OF 3 NUCLEOTIDES EACH SPECIFIES AN AMINO ACID THE CODE IS READ IN A CONTINUOUS FASHION WITHOUT SPACES OR PUNCTUATION.

DNA and RNA Triplet Code specifies one amino acid

DNA and RNA GENETIC CODE IS PRACTICALLY UNIVERSAL Suggests ALL CELLS originate from a common ancestor Genes transcribed by one organism can be translated by another Mitochondrial & Chloroplast DNA are exceptions

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DNA and RNA TRANSCRIPTION: That process of faithfully copying the information from DNA to an RNA molecule, i.e. Messenger RNA (mRNA) 1. Initiation 2. Elongation 3. Termination

DNA and RNA TRANSCRIPTION Transcription Bubble

DNA and RNA TRANSCRIPTION Transcription Bubble 3’ 5’

DNA and RNA TRANSCRIPTION: 1. INITIATION: RNA Polymerase II binds to PROMOTER Approx. 60 bp long Located at beginning of gene NOT transcribed Eukaryote’s promoter = TATA BOX named for code of TATAAAT Represents “START” site for RNA polymerase II

DNA and RNA TRANSCRIPTION: 2. Elongation: DNA Template strand read 3’→ 5’ mRNA synthesized 5’→ 3’ Process more complex in eukaryotes Elongation proceeds to end of gene sequence

DNA and RNA TRANSCRIPTION: 3.Termination: RNA Pol II recognizes a stop signal termination sequence on DNA Causes separation of enzyme from both DNA and RNA Mechanism different in prokaryotes and eukaryotes

DNA and RNA

INTRONS: Present in eukaryotes (not bacteria) Segments of mRNA that do not code “Intervening Segments” Part of “Primary” mRNA (unedited) Need to be “edited” prior to mRNA leaving the nucleus Introns 10-30X larger than EXONS

DNA and RNA EXONS: “Expressed Segments” of mRNA Shorter sequences than “Introns” Spliced together after removal of Introns to form functional mRNA Splicing occurs with “SPLICESOME”

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DNA and RNA

TRANSLATION: Polypeptide chain synthesized Each CODON specifies an AA in the peptide chain or a “start” or “stop” Translation includes 1. Initiation 2. Elongation 3. Termination

DNA and RNA GENETIC CODE 64 Codons for Individual AA Similar diagram Miller & Levine Page 303

DNA and RNA Transfer RNA (tRNA) Synthesized by RNA Polymerase III Two active sites: Amino acid accepting end Anticodon (complementary to mRNA codon) Approximately 45 different tRNA “Wobble Hypothesis”

DNA and RNA tRNA Always CCA

DNA and RNA Transfer RNA (tRNA): Aminoacyl Transferase catalyzes the addition of specific AA to tRNA tRNA attaches to “A Site” of ribosome No tRNA exists for UAA UAG UGA “STOP” CODONS

DNA and RNA Initiation begins with assembly of ribosome Using fMet tRNA at the “P site”. Anticodon

DNA and RNA

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DNA and RNA TRANSLATION: 1. Initiation: Initiation Factors become attached to the small ribosomal subunit Attach to the “Start” codon (AUG) of the mRNA Large ribosomal subunit binds to the small creating a functional ribosome

DNA and RNA TRANSLATION: 2. Elongation: tRNA with AA joins to “A Site” of ribosome (Aminoacyl Site) Ribosome moves from 5’ to 3’ PEPTIDE BOND forms between AA TRANSLOCATION occurs tRNA leaves from “E Site” (Exit Site)

DNA and RNA TRANSLATION: 3. Termination: “Stop” codon has no tRNA Empty site filled with “Release Factor” Release Factor catalyzes hydrolysis of tRNA to peptide chain Polypeptide released

DNA and RNA

POLYSOME (Polyribosome) In prokaryotes, Transcription & Translation may occur together Multiple ribosomes may attach to emerging mRNA Multiple strands of identical protein formed simultaneously

DNA and RNA Polysomes

DNA and RNA REGULATION OF GENES: OPERON: CONSISTS OF PROMOTER OPERATOR PROTEIN CODING GENES

DNA and RNA REGULATION OF GENES: REPRESSIBLE OPERONS: “trp” Operon: Normally “on” Repressor protein Allosteric inhibition

DNA and RNA

REGULATION OF GENES: INDUCIBLE OPERONS: “lac” Operon: Normally “Off” Repressor always active Allosteric control of repressor protein

DNA and RNA

Repressible Enzymes function in Anabolic Pathways Synthesize essential end-products from raw materials Inducible Enzymes function in Catabolic Pathways Break down nutrients to simpler molecules

DNA and RNA MUTATIONS: A. CHROMOSOMAL MUTATIONS: 1. Deletions 2. Duplications 3. Inversions 4. Translocations

DNA and RNA

MUTATIONS; B. POINT MUTATIONS: 1. Silent 2. Missense ( Replacement ) 3. Nonsense 4. Frameshift

DNA and RNA