From Gene to Protein Chapter 17

What you need to know: The key terms: gene expression, transcription, and translation. The major events of transcription. How eukaryotic cells modify RNA after transcription. The steps to translation. How point mutations can change the amino acid sequence of a protein.

Concept 17.1: Genes specify proteins via transcription and translation

_____________________: process by which DNA directs the synthesis of proteins (or RNAs) Old idea: one ________ - one ____________ hypothesis Proposed by Beadle & Tatum – mutant mold experiments Function of a gene = dictate production of specific enzyme Newer idea: one gene - one ______________ hypothesis Most accurate: one gene - one ______ molecule (which can be translated into a polypeptide)

Flow of genetic information CENTRAL DOGMA: DNA  RNA  protein __________________: DNA  RNA _________________: RNA  protein ____________ = site of translation

Flow of Genetic Information in Prokaryotes vs. Eukaryotes

one gene = one RNA molecule DNA RNA Nucleic acid composed of nucleotides ___________ -stranded ___________ = sugar ___________ Many different roles! Nucleic acid composed of nucleotides ___________ -stranded _____________ = sugar _____________ Template for individual

________ plays many roles in the cell _________________=precursor to mRNA, newly transcribed and ____________________ mRNA= the edited version; ______________ the code from DNA that specifies amino acids tRNA= carries a specific __________________to ribosome based on its ______________ to mRNA codon rRNA= makes up 60% of the ____________________; site of protein synthesis snRNA= ___________________RNA; part of a ________________. Has structural and ___________ roles srpRNA=a signal recognition particle that binds to signal peptides RNAi= ________________ RNA; a ____________ molecule ribozyme= RNA molecule that functions as an ___________

The Genetic Code For each gene, one DNA strand is the ___________ strand mRNA (5’  3’) _____________ to template mRNA triplets (__________) code for amino acids in polypeptide chain

The Genetic Code 64 different codon combinations _______________: 1+ codons code for each of 20 AAs Reading frame: groups of ___must be read in correct groupings This code is universal: __________________ __________________.

Concept 17.2: Transcription is the DNA-directed synthesis of RNA

Transcription Transcription unit: stretch of _______ that codes for a ______________ or ________ (eg. tRNA, rRNA) _______________________________: Separates _____ strands and _____________ mRNA mRNA elongates in ___  ___ direction Uracil (U) replaces thymine (T) when pairing to adenine (A) Attaches to __________________ (start of gene) and stops at ____________________ (end of gene)

1. Initiation Bacteria: RNA polymerase binds ___________ to promoter in DNA

1. Initiation Eukaryotes: ___________= DNA sequence (TATAAAA) _____________ from promoter _______________ _____________ must recognize TATA box before RNA polymerase can bind to DNA promoter

2. Elongation __________________adds RNA nucleotides to the ____ end of the growing chain (A-U, G-C)

2. Elongation As RNA polymerase moves, it untwists DNA, then rewinds it after mRNA is made

3. Termination RNA polymerase transcribes a _________________ sequence in DNA, then mRNA and polymerase detach. It is now called __________________ for eukaryotes. __________________ = mRNA ready for use

Flow of Genetic Information in Prokaryotes vs. Eukaryotes

Concept 17.3: Eukaryotic cells modify RNA after transcription

Additions to pre-mRNA: ____________ (modified guanine) and 3’ _____________(50-520 A’s) are added Help __________from nucleus, protect from enzyme ____________, attach to _____________

RNA Splicing Pre-mRNA has introns (____________ sequences) and _________________ (codes for amino acids) ______________ = __________ cut out, exons joined together

Ribozyme = ______ acts as ___________________ RNA Splicing small nuclear ribonucleoproteins = snRNPs snRNP = snRNA + protein Pronounced “snurps” Recognize splice sites snRNPs join with other proteins to form a ________________ Spliceosomes catalyze the process of removing introns and joining exons Ribozyme = ______ acts as ___________________

Why have introns? Some regulate _____ activity Alternative RNA Splicing: produce different combinations of exons One gene can make more than one polypeptide! 20,000 genes  100,000 polypeptides

Concept 17.4: Translation is the RNA-directed synthesis of a polypeptide

Components of Translation mRNA = _______________ tRNA = ________________ Ribosome = ____ of translation

tRNA Transcribed in _____________ __________ to each amino acid ___________ AA to ribosomes Anticodon: pairs with complementary mRNA _______ Base-pairing rules between 3rd base of codon & anticodon are not as strict. This is called __________________.

tRNA Aminoacyl-tRNA-synthetase: enzyme that binds tRNA to specific amino acid

Ribosomes Ribosome = _________ + ___________ made in _________________ __ subunits

Ribosomes Active sites: __ site: holds AA to be added __ site: holds growing polypeptide chain __ site: _____ site for tRNA

Translation: 1. Initiation __________ subunit binds to start codon (AUG) on mRNA tRNA carrying Met attaches to ___ site __________ subunit attaches

2. Elongation ________ over and over _______ recognition: tRNA anticodon matches codon in A site ________________: tRNA in A site moves to P site; tRNA in P site moves to E site (then exits) _________________ formation: AA in A site forms bond with peptide in P site

3.Termination ___________ codon reached and translation stops Release factor binds to stop codon; polypeptide is released Ribosomal subunits dissociate

Polyribosomes A single mRNA can be translated by ___________ ribosomes at the same time

Protein Folding During synthesis, polypeptide chain coils and folds spontaneously _________________________: protein that helps polypeptide fold correctly

Types of Ribosomes ________ ribosomes: synthesize proteins that ___________________________ and function there __________ ribosomes (to ER): make proteins of _____________________ ____________ (nuclear envelope, ER, Golgi, lysosomes, vacuoles, plasma membrane) & proteins for ______________ Uses ______________ peptide to target location

Cellular “Zip Codes” Signal peptide: 20 AA at leading end of polypeptide determines destination Signal-recognition particle (SRP): brings ribosome to ER

Concept 17.5: Point mutations can affect protein structure and function

The Central Dogma ________________ happen here _________________ play out here

Mutations = changes in the genetic material of a cell Large scale mutations: _________________; always cause disorders or death _______________, _______________, inversions, duplications, large deletions Point mutations: alter _________________of a gene Base-pair _________________ – replace 1 with another ____________________: _________________ amino acid ____________________: ______ codon, not amino acid ________________________ – mRNA read incorrectly; _____________________ proteins Caused by _________________ or __________________

Substitution = __________________

Substitution = _______________________

Substitution = _____________ (no effect)

Insertion = _________________ Mutation

______________ = Extensive missense, premature termination

Pulmonary hypertension Sickle Cell Disease Symptoms Anemia Pain Frequent infections Delayed growth Stroke Pulmonary hypertension Organ damage Blindness Jaundice gallstones Caused by a genetic defect Carried by 5% of humans Carried by up to 25% in some regions of Africa Life expectancy 42 in males 48 in females

Sickle-Cell Disease = Point Mutation

Mutation occurs in the beta chain – have them look at their amino acid structures and think about why the change may be important

Sickle cell hemoglobin forms long, inflexible chains

Comparison: Prokaryotes vs. Eukaryotes

Prokaryote vs. Eukaryote

Prokaryotes vs. Eukaryotes Transcription and translation ______ in ____________ DNA/RNA in __________ RNA polymerase binds __________ to promoter Transcription makes ______ (not processed) No ___________ Transcription in ________; translation in ___________ ______ in nucleus, ______ travels in/out nucleus RNA polymerase binds to _____________ & ______________ factors Transcription makes ____- mRNA  _____________  final mRNA Exons; introns (_________)

A Summary of Protein Synthesis (p. 348) Most current definition for a gene: A region of DNA whose final product is either a polypeptide or an RNA molecule