dna , protein synthesis, and gene expression
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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 - PowerPoint PPT PresentationTRANSCRIPT
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
(PO4) 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)
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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
(PO4) 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 ______________ 500-4500 bases; depending on size of gene Every three bases are called a ___________
tRNA- 75-80 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)- 100-3000 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
1⁰- ________________________________ 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