Protein Synthesis

1. Protein Synthesis DNA  RNA Proteins

2. Do Now: • Summarize the structure and function of genes • Describe the function of ribosomes • Differentiate between DNA and genes • Describe the structure and function of DNA • State the base pairing rules

3. Summarize the structure and function of genes: Part of a DNA molecule that codes for a certain trait Describe the function of ribosomes: Site of protein synthesis Differentiate between DNA and genes: Genes are PART of a DNA molecule Describe the structure and function of DNA: Organized into 46 strands of chromatin State the base pairing rules: A-T, C-G Do Now:

4. RECALL THE FOLLOWING • The cell cycle is a repeating series of steps of growth and development, that results in two new daughter cells identical to the parent cell • During S phase (Interphase), each strand of DNA copies itself, so that each daughter will get one copy • DNA is found in the nucleus

5. RECALL THE FOLLOWING • DNA carries the code for all of the traits that make you human, as well as those that make you an individual • Each gene in your body carries a code for a different protein – and these proteins result in different traits (eye color, hair color, enzymes, etc.) • Proteins are made on the ribosomes • Ribosomes are found in the cytosol

6. So…how then do we get from DNA (in the nucleus) to proteins (in the cytosol)?

7. RNA (Ribonucleic Acid) • Single Strand of Nucleotides • 5 C sugar is ribose (Remember in DNA the sugar was Deoxyribose) • Uses the N base uracil (U) instead of thymine (T) • 3 Types: • All 3 types of RNA are essential for processing information from DNA to proteins.. Gene Expression or Protein Synthesis • Messenger RNA (mRNA) • An RNA copy of the gene • Carries and delivers genetic info from nucleus to ribosome • Ribosomal RNA (rRNA) • Makes up a ribosome • Site of translation • Transfer RNA (tRNA) • Acts as an interpreter • Translates mRNA into amino acid sequences

8. Gene Expression • Organisms traits are determined by proteins • Proteins are assembled according to genes on DNA • DNA can not leave the nucleus, but proteins are made in ribosomes, therefore need an intermediate messenger… RNA • 2 stages: • Transcription – copying DNA info to mRNA (nucleus) • Translation – mRNA used to build protein (cytoplasm)

9. Transcription • RNA polymerase binds to promoter region of DNA • Promoter region – specific sequence of DNA that serves as a START signal (RNA is only transcribed one gene at a time) • DNA unwinds and 2 strands separate • only 1 side is used as a template • RNA polymerase reads each nucleotide and pairs it with a complimentary RNA nucleotide • Same base pairing rules except “U” pairs with “A” • RNA dangles off the enzyme like a tail • Proceeds at 60 nt/sec until RNA polymerase reaches a specific STOP sequence • mRNA is processed • mRNA is a copy of exons (coding) and introns (non-coding) regions • Introns are cut out before mRNA leaves the nucleus • Introns allow for evolutionary flexibility, genes to shuffle, and limits effects of mutations • mRNA leaves nucleus and attaches to a ribosome

10. Transcription • DNA: T T A C C G G T T A G G • mRNA: A A U G G C C A A U C C

11. Transfer RNA • Carries the associated amino acid to the mRNA molecule • Is a single strand that loops around • One end has an anti-codon (complementary to codon) • Other end carries the amino acid that cooresponds

12. mRNA and tRNA • tRNA

13. The Genetic Code • The Genetic Code • Instructions for building a protein are written as codons on mRNA • Codons – 3 nt that code for a specific a.a. • Codon chart - a.a. and stop signals that are coded by each of possible sequences of mRNA codons • Universal – the genetic code is the same in ALL organisms… suggests a common ancestor • Ex. GUC codes for the a.a. valine in bacteria, dogs, lizards, humans, etc • Reading the codon chart

14. Alternate Genetic Code Chart: Find a.a. for AUG-GGC-UAA

15. Translation • tRNA – one loop has 3 nt sequence called an anticodon • Anticodon – 3nt complimentary to codon on mRNA • Enables tRNA to temporarily H-bond to mRNA • No tRNA w/anticodons for STOP codons UAG, UAA, UGA • tRNA also carries the a.a. that corresponds to CODON • Ribosomes • 1,000’s in cytoplasm • 2 rRNA subunits (large and small) bind together to form ribosome • 3 Binding Sites • A site – where tRNA anticodon binds to complimentary codon of mRNA • P site – holds tRNA w/ growing polypeptide chain • E site – tRNA exits, leaving a.a. in the “P” site

16. Do Now: • DNA sequence: TAC CCG CAC GGT TTT AAA ACT • What are the mRNA codons? • What are the tRNA anticodons? • What is the amino acid sequence?

17. Translation: Assembling the Protein • mRNA binds to small rRNA subunit w/start codon, AUG, in the “P” site • tRNA w/ anticodon UAC and carrying a.a. methionine binds to start codon • The next codon, in “A” site, binds w/ complimentary tRNA (carrying the corresponding a.a.) • Enzyme forms a peptide bond between adjacent a.a. • tRNA in “P” site now exits via “E” site and is recycled • tRNA in the “A” site moves to the “P” site w/ growing polypeptide chain, mRNA moves w/it, therefore a new codon is in the “A" site • Process continues until it reaches a STOP codon at the end of the mRNA, there is no anticodon • W/nothing in the “A” site, the ribosome is disassembled and the newly made polypeptide is released

18. Protein Synthesis

19. Mutations • Mutation – any change in an organism’s genetic material • Causes • Mutagens – environmental agents that cause mutations after exposure • X-rays, UV rays, chemicals • Carcinogens – mutagens that lead to cancer • Asbestos, benzene, tobacco

20. Types of Mutations • Chromosomal Mutations • Alterations in chromosome structure • Deletion, duplication, inversion, translocation • Point Mutations • Just one or a few nt changed in a gene • Substitution – one nt is replaced by a different nt • Ex. UGU  UGC (no effect b/c both code for cysteine) • UGU  UGA (early STOP codon) • Frameshift mutations • Mutations that cause a gene to be read in the wrong 3 nt sequence • Insertions – one or m ore nt added to gene • Ex. AAU CGC UUU • AGA UCG CUU U • Deletions – one or more nt deleted from gene • Ex. AAU CGC UUU • AUC GCU UU Note * If mutation occurs in an intron it will have no effect *if reading frame is displaced 3 nt, the mutation may have no effect

21. Prokaryotic Gene Regulation • Prokaryotic Cells – genes are unbroken set of nt • Operon • controls gene expression in prokaryotes • Cluster of genes that code for proteins w/related functions

22. Lac Operon • Lac Operon – genes for lactose digesting enzyme..lactase • Only want lactase when lactose is present…or else energy is being wasted transcribing genes • Operator – acts like an on/off switch • If no molecule is bound to operator, then the gene is “ON” and RNA polymerase can move across • When a repressor protein binds to the operator, it blocks the RNA polymerase from transcribing, genes are “OFF” • Repressor can be removed by inducer (ex. allolactose), now gene is turned ‘ON” • http://www.sumanasinc.com/webcontent/animations/content/lacoperon.html

23. Eukaryotic Gene Regulation • No operons…b/c genes w/similar functions are scattered among different chromosomes • Multicellular organisms have different types of cells, all somatic cells contain the same DNA…but what makes them different is which genes are turned on/off • Ex. Every cell has hemoglobin genes, but only turned “ON” in rbc • Transcription takes place at uncoiled regions of chromosome • RNA polymerase cannot bind w/o transcription factors • Transcription factors are signaled by 20 messengers that bind to the enhancer site to turn “ON” the gene