Download Dna, Protein Synthesis, and gene expression

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
_________________
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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
(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




tRNA



Copy of DNA instructions
Also called ______________
500-4500 bases; depending on size of gene
Every three bases are called a ___________
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

If DNA is T
 Then

RNA is ___
If DNA is C
 Then

RNA is ___
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


Poly A tail


G base is inverted and _____________
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)


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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

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
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1⁰- ________________________________
2⁰- localized folding (α- helix and β-sheet)
3 ⁰- _________ polypeptide folds together
4 ⁰- ________________ polypeptide folds together
Protein Folding (cont)
Gene Expression



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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


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Do not code for protein
RNA’s besides mRNA
Introns
Promotors and control regions
Repeats
 Transposons-
chromosomes
 Telemeres
 Centromeres
repeats that can move and insert into new