Bell ringer: Describe what is occurring with each of the following mutations Frameshift Deletion Substitution What is the name of the enzyme that makes telomeres? In what direction is DNA replicated? What is the function of RNA primase?

RNA vs. DNA structure

Types of RNA RNA is a polymer of RNA nucleotides RNA Nucleotides are of four types: Uracil, Adenine, Cytosine, and Guanine Uracil (U) replaces thymine (T) of DNA Types of RNA Messenger (mRNA) - Takes genetic message from DNA in nucleus to ribosomes in cytoplasm Ribosomal (rRNA) - Makes up ribosomes which read the message in mRNA Transfer (tRNA) - Transfers appropriate amino acid to ribosome when “instructed”

DNA Repair Errors occur 1/10 billion nucleotides Mismatch repair (Humans have 3 billion base pairs in their DNA) Mismatch repair DNA polymerase (yes…it’s 3rd function) “Proofread” new DNA Like the “delete” key on computer Excision (“cut out”) repair Nuclease

DNA Repair

Replication: Prokaryotic Prokaryotic Replication Bacteria have a single circular loop Replication moves around the circular DNA molecule in both directions Produces two identical circles Cell divides between circles, as fast as every 20 minutes

Replication: Prokaryotic vs. Eukaryotic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. origin replication is complete replication is occurring in two directions a. Replication in prokaryotes replication fork replication bubble parental strand new DNA duplexes b. Replication in eukaryotes daughter strand

Protein Synthesis: Transcription & Translation Unit 4: DNA Chapter 13 DNA > mRNA > ribosome > protein

Protein Synthesis Overview Two processes are required: 1. Transcription: DNA > mRNA 2. Translation: mRNA > protein

Transcription: DNA > mRNA Process of making messenger RNA (mRNA) from a DNA template to take the DNA info outside of the nucleus

Bellringer Write the questions and answers What is the difference between DNA and RNA in regards to structure and bases What is the central dogma of molecular genetics? What is the process of transcription? List the three types of RNA

DNA can NOT leave the nucleus (too big) Messenger RNA (mRNA) carries the info encoded in DNA out of the nucleus to the ribosomes located in the cytoplasm.

Steps of Transcription 1. DNA strands unwind & separate 2. DNA strand containing a specific gene serves as a template strand 3. RNA nucleotides are matched to complimentary DNA bases 4. mRNA molecule is complete and DNA rewinds

Bell Ringer (write the question) What are the building blocks of proteins? What enzyme relaxes the DNA strand? Where is the replication fork assembled at? (hint where does DNA replication take place) True/False prokaryotic DNA consist of telomeres

mRNA Processing Introns: the mRNA contains extra info (junk) that must be removed (cut out) Exons: the remaining pieces carry useful information are spliced (connected) together to make the complete mRNA

The bases of mRNA pair with DNA bases but RNA replaces T with U DNA: C T G T A C G G A ---> Transcription mRNA: G A C A U G C C U DNA RNA A U T G C template strand

Check: Are there any T’s in your mRNA? Now you try… Based on the DNA template, create the matching mRNA strand: DNA: C T A T G C A A A C T A T A G mRNA: ______________________________ G A U A C G U U U G A U A U C Check: Are there any T’s in your mRNA? There shouldn’t be!!!

Translation: mRNA > protein Process of making proteins from info on mRNA mRNA travels out of nucleus to the ribosome, which “reads” the mRNA as a series of 3 letter words called codons

Bellringer Write the questions and answers The process of converting Dna to Mrna is called? The process of converting Mrna to a protein is called? change this Dna molecule into Mrna AATGCAATGGCCA 4. Where does transcription occur? where does translation?

Codon: 3-base code on mRNA that codes for a specific amino acid Ex. CGU = alanine GUU = valine The sequence of bases in DNA tell mRNA what order amino acids must join together to make a particular protein.

Codons found in mRNA

Transfer RNA (tRNA) matches up with each codon and transfers the correct amino acid Each tRNA molecule has 3 unpaired bases called the anticodon that is complementary to one mRNA codon.

Each amino acid is added to a growing chain of amino acids Protein = peptide bonds connecting amino acids Many different types of proteins exist because the number and sequence of amino acids can be different

Codons found in mRNA Practice translating mRNA into amino acids: mRNA: AUG AAA AGU UGU CUG GUU UAA A.A: ______________________________________ Met - Lys – Ser - Cys – Leu – Val - Stop

How DNA determines proteins DNA molecules serve as templates for making messenger RNA molecules Messenger RNA molecules move to ribosomes Transfer RNA molecules bring amino acids to the ribosome Polypeptides (proteins) are formed as ribosomes move along the messenger RNA strand

Gene Expression DNA in all of your body cells is the same! Ex: DNA in your eye cells is the same DNA that is in your skin cells. Different types of cells express different genes. Ex: Your eyes may be green, while your skin is brown. Specialization of cells is due to different patterns of gene expression, rather than different genes themselves. Liver cells express different genes than blood cells

DNA: TAC TCC AGC GCA ACT ----Transcription----> mRNA: AUG AGG UCG CGU UGA ----Translation---> A.A.: met arg ser arg stop

Bell ringer What occurs in translation? What is the role of rRNA? What is the role of tRNA? Transfer RNA (tRNA) matches up with each codon and transfers the correct amino acid, the match is called _______

Mutations Mutations are heritable changes in genetic information. Gene mutations Points mutations: substitutions, insertions, deletions (also called frameshift mutations)

Mutations

Chromosomal Mutations Deletion Duplication Inversion translocation

Review Genetic Material DNA Structure DNA Replication Transcription Transformation DNA Structure Watson and Crick DNA Replication Prokaryotic versus Eukaryotic Replication Errors Transcription Translation Structure of Eukaryotic Chromosome

Steps in Translation: Initiation Components necessary for initiation are: Small ribosomal subunit mRNA transcript Initiator tRNA, and Large ribosomal subunit Initiation factors (special proteins that bring the above together) Initiator tRNA: Always has the UAC anticodon Always carries the amino acid methionine Capable of binding to the P site

Steps in Translation: Initiation Small ribosomal subunit attaches to mRNA transcript Beginning of transcript always has the START codon (AUG) Initiator tRNA (UAC) attaches to P site Large ribosomal subunit joins the small subunit

Steps in Translation: Initiation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amino acid methionine Met initiator tRNA E site P site A site mRNA U A 5' A C U G 3' Met small ribosomal subunit large ribosomal subunit U A C A U G 5' 3' start codon A small ribosomal subunit binds to mRNA; an initiator tRNA pairs with the mRNA start codon AUG. The large ribosomal subunit completes the ribosome. Initiator tRNA occupies the P site. The A site is ready for the next tRNA. Initiation

Steps in Translation: Elongation “Elongation” refers to the growth in length of the polypeptide RNA molecules bring their amino acid fares to the ribosome Ribosome reads a codon in the mRNA Allows only one type of tRNA to bring its amino acid Must have the anticodon complementary to the mRNA codon being read Joins the ribosome at it’s A site Methionine of initiator is connected to amino acid of 2nd tRNA by peptide bond

Steps in Translation: Elongation Second tRNA moves to P site (translocation) Spent initiator moves to E site and exits Ribosome reads the next codon in the mRNA Allows only one type of tRNA to bring its amino acid Must have the anticodon complementary to the mRNA codon being read Joins the ribosome at it’s A site Dipeptide on 2nd amino acid is connected to amino acid of 3nd tRNA by peptide bond

Steps in Translation: Elongation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Met Met asp Met peptide bond Met tRNA Ser Ser Thr Ser Ser Ala Ala Ala C U G Ala Trp peptide bond Trp U G G Trp anticodon Trp Val Val Val Val Asp Asp Asp A U C A U C A U C U G C U G C C A U C U G G U A G A C G U A G A C G U A G A C G U A G A C A C C 3 3 6 6 3 6 3 1 A tRNA–amino acid approaches the ribosome and binds at the A site. 2 Two tRNAs can be at a ribosome at one time; the anticodons are paired to the codons. 3 Peptide bond formation attaches the peptide chain to the newly arrived amino acid. 4 The ribosome moves forward; the “empty” tRNA exits from the E site; the next amino acid–tRNA complex is approaching the ribosome. Elongation

Steps in Translation: Termination Previous tRNA moves to P site Spent tRNA moves to E site and exits Ribosome reads the STOP codon at the end of the mRNA UAA, UAG, or UGA Does not code for an amino acid Polypeptide is released from last tRNA by release factor Ribosome releases mRNA and dissociates into subunits mRNA read by another ribosome

Steps in Translation: Termination Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Asp Ala release factor Trp Asp Val Ala Glu Trp V al U U A A U G A Glu 5' stop codon 3' The ribosome comes to a stop codon on the mRNA. A release factor binds to the site. U U C U G A A G A 3 5 The release factor hydrolyzes the bond between the last tRNA at the P site and the polypeptide, releasing them. The ribosomal subunits dissociate. Termination

Summary of Gene Expression (Eukaryotes) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. TRANSCRIPTION TRANSLATION 1. DNA in nucleus serves as a template for mRNA. DNA 3. mRNA moves into cytoplasm and becomes associated with ribosomes. 2. mRNA is processed before leaving the nucleus. mRNA large and small ribosomal subunits 5 pre-mRNA introns 3' mRNA amino acids peptide 4. tRNAs with anticodons carry amino acids to mRNA. nuclear pore ribosome tRNA U A C U 5 G 3 A C A U anticodon codon 5. During initiation, anticodon-codon complementary base pairing begins as the ribosomal subunits come together at a start codon. C 8. During termination, a ribosome reaches a stop codon; mRNA and ribosomal subunits disband. C C 5 C C C U G G U U U G G G A C C A A A G U A 3' 6. During elongation, polypeptide synthesis takes place one amino acid at a time. 7. Ribosome attaches to rough ER. Polypeptide enters lumen, where it folds and is modified.

Structure of RNA P G G U S A P U base is uracil instead of thymine C S Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P G G U S A P U base is uracil instead of thymine C S P A S P C S ribose one nucleotide

Bell ringer What enzyme is responsible for making RNA strand? What is the function of SSBP? Describe the structure of DNA? Provide an example of a Deletion mutation

Bell ringer: List the steps of transcription True/false messanger RNA contains the nucleotide thymine True/false DNA can leave the nucleus through nuclear pores DNA is copied in what direction?