DNA, PROTEIN SYNTHESIS, AND GENE EXPRESSION

Inheritance

Search for the Genetic Code  Griffith’s Transformation Experiment (1928)

Avery, MacLeod, and McCarty (1944)  Repeated Griffith’s experiments  Used enzymes to destroy one of the _____________ during each round  Transformation was only stopped when ______ was destroyed

Hersey and Chase (1952)

Levene  Discovered the sugar difference between RNA and DNA  RNA- ____________  DNA- ____________  Discovered the components of a nucleotide  5-carbon __________  Phosphate group  Nitrogenous ________ (four types)

Chargaff  DNA contains equal amounts adenine (A) and thymine (T) and equal amounts cytosine (C) and guanine (G)  The amounts of A and T does _____ have to equal the amounts of C and G  Known as Chargaff’s rule

Franklin  Created X-ray diffraction images of DNA  Photo 51 allowed scientists to create a model of the sugar phosphate backbone (helix)  Close to figuring out bases  Picture shown to Watson and Crick without her knowing by colleague Wilkins

Watson and Crick  Able to make backbone based on Photo 51  First to propose structure of DNA  Watson, Crick, and Wilkins received Nobel Prize

DNA Nucleotides  Three Parts  Phosphate Group (PO 4 )  Deoxyribose  Nitrogenous Base Adenine (A) Guanine (G) Thymine (T) Cytosine (C)

DNA Bases  Pyrimidines- _________ structure; C and T  Purines- __________ structure; A and G

DNA Backbone  Composed of phospate groups and sugar  Strands of DNA are ______________  One runs 3’ to 5’; other runs 5’ to 3’

Complementary Base Pairing  A always pairs with T  Held together by ___ hydrogen bonds  C always pairs with G  Held together by ____ hydrogen bonds

Double Helix

DNA Coiling  Double Helix  ________________  Helix is wrapped around bundle of eight histone proteins (a pair of each of the four types)  Fifth type of histone anchors the nucleosome to linker regions of DNA  30 nm fiber- coiling of nucleosomes  _________ proteins- 30 nm fibers coil around the protein

Forms of DNA  __________- found throughout most of cell cycle  Chromosome- tightly packed DNA form during _________________

DNA Replication  Copy DNA into ______  Performed during ____ phase of Interphase  Occurs before division in mitosis and meiosis  ___________________  Each original DNA is still intact  Each original strand has a new partner (a newly made complement) <>

DNA Replication (cont)  Step 1- Unwinding of DNA stand  Performed by ____________  Held apart by binding proteins  Occurs at many replication fork along the length of the strand  Step 2- Formation of RNA primers  Performed by __________  Complementary base pairs are lined up to form the short primer

DNA Replication (cont)  Step 3- Replication  Performed by ___________________(DNAP)  DNAP can only attach bases to existing polymer (primer)  DNAP bring in complementary base pairs for each stand of DNA  Can only replicate in the ________ direction 3’ to 5’ original strand is replicated continously 5’ to 3’ is replicated discontinously in sections called Okazaki fragments

DNA Replication (cont)  Step 4- Sealing the Backbone  Performed by ____________  Bonds backbones of fragments together  Step 5- Proofreading  Performed by ___________  Checks bases and cuts out incorrect one to replace them with the correct one  Cuts out RNA primer and replaces with DNA nucleotides  Ligase seals all the backbones

From Gene to Protein  Genes code for protein; protein creates _________  Protein Synthesis- creating a protein  Transcription- _______________ Occurs in the ____________ DNA is copied into messenger RNA (mRNA) mRNA takes message to ___________  Translation- ______________ Occurs in cytoplasm at ____________ mRNA is decoded into amino acids Transfer RNA (tRNA) brings amino acids to ribosome

RNA Nucleotides  Three parts  Phosphate Group (PO 4 )  Ribose  Nitrogenous Base Adenine (A) Guanine (G) Uracil (U) Cytosine (C)

Ribosome Structure  Single Strand of Nucleotides  Shape will be determined by base pairing within the strand

Types of RNA  Three Major Types  mRNA- Copy of DNA instructions Also called ______________ bases; depending on size of gene Every three bases are called a ___________  tRNA bases that bind in cloverleaf shape One end bonds to a specific amino acid One end has a three base code called the _________  Ribosomal RNA (rRNA) bases long Form structure of ribosome with proteins ___________- catalyze peptide bond formation between amino acids

Transcription  Step 1- Initiation  _________ binding protein (transcription factor) binds to TATA box within gene promoter region  Other transcription factors bind to this area forming complex  RNA polymerase binds to complex  Step 2- Elongation  RNA polymerase adds RNA nucleotides complementary to DNA Only occurs in _______direction (reading the 3’ to 5’ DNA strand) DNA stand being copied is called the ________; the other DNA strand not being copied is the _________ strand The coding strand may be the template strand for another gene

Transcription (cont)  Step 3- Termination  RNA polymerase reaches a terminator sequence in DNA  Transcription is stopped  More than one transcript may be forming at a site at one time

Base Pairing Rules  If DNA is A  Then RNA is ___  If DNA is T  Then RNA is ___  If DNA is C  Then RNA is ____  If DNA is G  Then RNA is ___

Processing mRNA  Transcript is altered in the nucleus before it leaves  Cap is placed at 5’ end  G base is inverted and _____________  Poly A tail  Tail of around 200 adenines added to __________  Removal of Introns  Pre-mRNA still contains sections that don’t code for protein and must be spliced out of transcript  Some introns are ribozymes that associate with proteins to form small nuclear ribonucleoproteins (snRNP’s) that will preform the splicing  Final transcript only contains ___________

Processing mRNA (cont)

Consequences of Processing  We create more proteins than we have genes  How do we do it?  Alternate splicing- mRNA is spliced to be shorter or longer to create a different protein  Different use of introns and exons- same pre-mRNA may have different areas spliced depending on the protein to be made

Translation  Step 1- Initiation  mRNA leader sequence bond to small ribosome subunit  First codon (always AUG) bonds with tRNA anticodon (UAC); this type of tRNA always has methionine attached  Step 2- Elongation  Large subunit attaches to small subunit  First codon/anticodon are put in the P site  A site exposes the second codon  The matching tRNA anticodon base pairs with the exposed codon bringing its amino acid  A peptide bond forms between the amino acids (catalyzed by a ribozyme)  The mRNA shifts down a spot P site holds second codon with two amino acids attached A site exposes next codon to base pairs with a matching anticodon First tRNa (UAC) returns to cytoplasm to find another methionine

Translation (cont)  Step 3- Termination  Exposed codon at A site is one of the stop codons  No tRNA’s match; release factor binds and releases mRNA and poypeptide  mRNA may be translated by several ribosomes at the same time

Cystic Fibrosis

Protein Folding  Creates final ______________ of protein  Occurs in ER  Shape is created by  Attraction between neighboring amino acids  Polarity of amino acids  Sulfur bridges

Protein Folding (cont)  Chaperone proteins stabilize shapes as the form  Folding catalysts held fold protein  Folding sensors proofread shape  Misfolded proteins are tagged Can be refolded properly Could be destroyed by proteasome  1 ⁰- ________________________________  2⁰- localized folding (α- helix and β-sheet)  3 ⁰- _________ polypeptide folds together  4 ⁰- ________________ polypeptide folds together

Protein Folding (cont)

Gene Expression  Not all genes are expressed at the same time  An organisms expresses genes at different times in different areas  Each cell type will express a different subset of genes  This can be seen by looking at the ____________

What Effects Gene Expression?  Chromatin Remodeling  Histones can expose or shield gene; groups can be added to histone to change it Acetyl and phosphate groups- turn on gene when added ___________ groups- turn off gene when added  RNA interference (RNAi)  RNA form a double strand when a single strand makes a hairpin turn and bonds with itself  Dicer (enzyme) cuts the RNA into small segments called small interfering RNA’s (siRNA’s)  siRNA’s Methylate histones Attach to transcrpts, tagging them to be destroyed

Noncoding Regions of DNA  Do not code for protein  RNA’s besides mRNA  Introns  Promotors and control regions  Repeats  Transposons- repeats that can move and insert into new chromosomes  Telemeres  Centromeres