Exam #2 Content Flashcards
(161 cards)
1
Q
Proteins
A
Gene products, early evidence from mutations in metabolic pathways
2
Q
Archibald Garrod
A
Inborn errors of metabolism
-Alkaptonuria: showed the first case of recessive inheritance in humans
-Phenylketonuria
aka: blocks in metabolic pathways
3
Q
Phenylketonuria Block
A
Pathway to Phe to Tyrosine
-Newborn PKU test
-Phenylalanine hydroxylase
4
Q
Alkaptonuria Block
A
Homogenetic acid oxidase
-Homogenetic acid to maleylacetoacetic acid pathway
5
Q
Beadle and Tutum (1941)
A
Worked with mutants of fungus neurospora crassa ( a bread mould)
-Discovered that genes provide instructions for making protein
6
Q
One Gene: One Enzyme Hypothesis
AKA: One Gene: One Polypeptide Hypothesis
A
B&T proved garrods hypothesis that genes have a biochemical role
-There must be 1 gene responsible for synthesizing 1 enzyme
-Neurospora can synthesize nearly every biomolecule it needs
-Used radiation to induce mutations in neurospora
-Determined which biomolecule the mutant could no longer synthesize
7
Q
Adrian Srb and Norman Horowitz’s
A
Experiment with neurospora crassa mutants deficient in argenine production led to the biosynthetic pathways for argenine
8
Q
Folded Structure
A
Following translation polypeptides fold up and assume higher order structure and may interact with other polypeptides
-Cannot predict what folded structure is going to look like from amino acid sequence
9
Q
Primary Structure
A
Amino acid sequence or protein
-Polypeptide formation
-Peptide bonds hold amino acid sequence together
10
Q
Secondary Structure
A
Primary folds to form repeating shapes
-2 types: alpha helix and beta sheets
-Certain amino acids are better at making each bond
-Secondary structures are stabalized by the formation of H bonds btwn atoms located in the polypeptide back bone
11
Q
Tertiary Structure
A
Can be seen during translation
-Short regions of secondary structure fold into a 3D structure
-Structure determined by hydrophobic and ionic interactions and H bonds and Van Der Waals
-Final form of proteins that are composed of a single polypeptide
12
Q
Quaternary Structure
A
Most proteins do not have quaternary form
-Usually formed by proteins that are made up of more than 1 polypeptide
-Various polypeptides associate with one another to make a functional protein
13
Q
Mutations
A
Heritable change in genetic material
-Provide allelic variation
-Pro: foundation for evolutionary change
-Con: cause of many diseases
-b/c mutations can be harmful organisms have developed ways to repair damaged DNA
14
Q
Types of Mutations (3 Main types)
A
1.) Chromosome Mutations
2.) Genome Mutations
3.) Single Gene Mutations
15
Q
1.) Chromosome Mutations
A
Changes in chromosome structure
16
Q
2.) Genome Mutations
A
Changes in chromosome #
17
Q
3.) Single Gene Mutations
A
Relatively small changes in DNA structure that occur within a particular gene
18
Q
Human Hemoglobin
A
One gene encodes one polypeptide
-Sickle cell anemia
19
Q
Post-Translational Processing
A
Can modify polypeptide structure
-Cleavage may remove an amino acid
-Cleavage may split polyprotein
-Chemical constituent addition may modify a protein
20
Q
Single-Gene Mutations
A
Point Mutations
-Change of a single base pair
-base substitutions
-Transition and Transversion
21
Q
Point Mutations
A
Transition:
-change pyrimidine (C,T) to another pyrimidine
-change purine (A,G) to another purine
Transversion:
-change of pyrimidine (C,T) to purine (A,G) or purine to pyrimidine
Transitions are more common than Transversions
22
Q
Transition (Point Mutations)
A
Change pyrimidine (C,T) to another pyrimidine or purine (A,G) to another purine
-more common than Transversion
23
Q
Transversion (Mutations)
A
Change pyrimidine (C,T) to purine (A,G) or purine to pyrimidine
-less common than Transition
24
Q
Gene Mutations
A
Can alter the coding sequence within a gene
25
Silent Mutations
Base Substitution
-does not alter amino acids sequence of polypeptide
-does not alter sequence b/c genetic code is degenerate (more than 1 codon can code from a single amino acid)
26
Missense Mutations
Base Substitution
-does alter amino acid sequence
27
Nonsense Mutations
Base Substitution
-changes a normal codon to a termination/STOP codon
28
Frameshift Mutations
Addition/Deletion
-addition or deletion of nucleotides in multiples of one or two
-shifts the reading frame so that a completely different amino acid sequence occurs down downstream from the mutation
29
Mutation effect on Genotype and Phenotype
In natural populations the wild-type is the most common genotype
-Forward Mutations, Reverse Mutations, and Variants
30
Forward Mutations
Changes wild-type genotype into a new variation
31
Reverse Mutations
AKA: Reversion
Reverts the mutant allele back into the wild-type
-opposite of forward mutations
32
Variants
When a mutation alters an organisms phenotypic characteristics
-characterized by their differential ability to survive
-Deleterious Mutations, and Beneficial Mutations
33
Deleterious Mutations (Variant)
Decreases chances of survival
-most extreme: lethal mutations (interrupt an essential process and results in death)
34
Beneficial Mutations (Variant)
Enhanced survival and reproductive success or an organism
35
Conditional Mutants
Affect phenotype only under a defined set of conditions
-expression of conditional mutations depends on environment around organisms
e.g. temperature-sensitive mutation
36
Gene Mutations to Promoter
Mutations can alter promoter sequences
- Up promoter mutations, Down promoter mutations
37
Up Promoter Mutations
Make promoter more like the consensus sequence
-may increase rate of transcription
38
Down Promoter Mutations
Make promoter less like the consensus sequence
-may decrease rate of transcription
39
Mutations and Splicing
Mutations may affect a splice recognition sequence
-may alter ability of pre-mRNA to be properly spliced
40
Neutral Mutations
No positive or negative effects
-in humans a vast majority of mutations occur in the large portion of the genome that do not contain genes and therefore have no effect on gene products
-silent mutations are also neutral mutations
41
Phenotype and Mutations
Depends on how protein function is changed by a mutation
42
Null Mutation
No gene function
-no gene product or non-functional product
-usually recessive but can be dominant
43
Hypomorphic Mutations
Reduced gene function
-protein retains part of it's activity
-usually recessive but can be dominant
44
Hypermorphic Mutations
Enhances gene function
-protein functions more efficient
-usually dominant
-extremely rare
45
Neomorphic Mutations
Novel gene function
-protein has novel properties or is expressed ectopically
-at the wrong place or at the wrong time
-dominant
46
Mutations
Can occur spontaneously or be induced
47
Spontaneous Mutations
Result from abnormalities in cellular/ biological processes
-underlying cause originates in with in the cell
-e.g. errors in DNA replication
48
Induced Mutations
Caused by environmental agents
-agents that are known to alter DNA structure are termed: Mutagens
49
Mutagens
Can be chemical or physical agents
-agents known to alter DNA structure
-alter DNA structure in different ways
-e.g. radiation
50
Frequency of Gene Mutations
(How often mutations happen)
Very rare: b/c of mechanisms that protect against or repair mutations
-frequencies show great variation depending on type of gene and organisms
-range: 1 mutation in a gene in 10^4 to 10^8 gametes
-mutations rates differ b/c of gene size in nucleotide sequence and others
51
Luria-Delbruck Fluctuation
Demonstrated that mutations are not adaptive but occur spontaneously
52
Luria and Delbruck Experiment and Hypothesis
Studied resistance of E.Coli to bacteriophage
-ton^r (T one resistance)
-Hypothesis: is ton^r due to spontaneous mutations or to a physiological adaptation that occurs at a low rate
-became known as the "fluctuation test"
53
Luria and Delbruck theories
*Physiological adaptation theory
-predicts that the # of ton^r bacteria is essentially constant in different bacterial populations
*Spontaneous Mutation theory (proven right)
-the # of ton^r bacteria will fluctuate in different bacteria populations
54
Causes of Spontaneous Mutations
Spontaneous mutations can arise by chmeical changes (spontaneous lesions on DNA molecule)
1.) Depurination (most common)
2.) Deamination
3.) Oxidation
4.) Tautomeric Shift
55
1. Depurination (Cause of Spontaneous Mutations)
Involves removal of purine (A or G) from DNA
-covalent bond btwn deoxyribose and a purine base is somewhat unstable, and occasionally undergoes a spontaneous rxn w/ water that releases base from sugar
-site where that happens is called a apurinic site
56
Apurinic site
Site in depurination where base is released from sugar
-site can be repaired
- if repair system fails, a mutation may result during subsequent rounds of DNA replication
Apurinic site-> transversions
-usually replaced by T
-Apyrimidinic site also occur but less frequently
57
2. Deamination (Cause of Spontaneous Mutations)
Spontaneous lesions
C->T :Transition
58
3. Oxidation (Cause of Spontaneous Mutations)
DNA may suffer oxidation damage by the by-products of normal cellular processes
H2O2: hydrogen peroxide
OH: hydroxyl radicals
O2: Superoxide radicals
G->T :Transversion
59
Tautomer and Tautomeric Shifts
Isomers that differ in a single proton shift in the molecule creating a change in the bonding structure of the molecule
-purine and pyrimidines can exits in one of several forms
60
4. Tautomeric Shifts (Cause of Spontaneous Mutations)
In nucleotides can result in mutations due to anomalous base pairings
61
Important Tautomer's
-Keto (standard): -enol (anomalous) former thymine and guanine
-Amino (standard): -imino (anomalous) forms of cytosine and adenine
-these shifts allow hydrogen bonding with noncomplementary bases
62
Induced Mutations
Caused by environmental agents
-arise from DNA damage caused by chemicals or radiation
63
Chemical Mutagens
3 types:
-Base modifiers (alter base)
-intercalating agents (destroy double helix)
-Base analogues (disguised as bases)
64
Base Modifiers (Chemical Mutagen)
Covalently modify structure of a nucleotide
-Nitrous acid: replaces amino groups with Keto groups (NH2 to double bonded O)
-causes deamination
-modified bases do not pair with appropriate nucleotides in daughter strand (can change C to U, A to hypoxanthire)
65
Intercalating Agents (Chemical Mutagen)
Flat planar structures that intercalate or insert themselves into double helix
-distort helical structure
-DNA with these mutagen is replicated daughter strand may contain single-nucleotide additions and/or deletions resulting in frame shift
-acridine dyes: cause frameshift by intercalating btwn purines and pyrimidine
-proflavin
66
Base Analogs (Chemical Mutagen)
Substitute for purines and pyrimidines during nucleic acid replication
-become incorporated into daughter during DNA replication
-5-bromouracil-thymine analogue can be incorporated into DNA instead of thymine
-promote change of AT pair to GC pair in DNA replication
67
The Ames Test
Used to assess the mutagenicity of compounds
-uses strains of salmonella typhimuriam selected for increased sensivity to mutagens and their ability to reveal mutations
-many known carcinogens have been shown by the Ames test to be strong mutagens
68
Physical Mutagens (Induced Mutations)
-Ionizing Radiation
-Non-Ionizing Radiation
69
Ionizing Radiation (Physical Mutagens: Induced Mutations)
X-Rays and Gamma rays
-short wavelength and high energy
-can penetrate deeply into biological molecules
-can cause: double-strand break, deletions, and inversions
70
Mutations Frequency
Mutation Frequency increases linearly increased does of radiation
71
Electromagnetic Spectrum and Radiation
Short wavelength, high energy
-gamma (ionizing)
-x-rays (ionizing)
-infrared (ionizing)
-Visible light (non-ionizing)
-ultra violet (non-ionizing)
-microwaves (non-ionizing)
-radio waves (non-ionizing)
72
Non-Ionizing Radiation (Physical Mutagens: Induced Mutations)
Includes UV light
-less energy
-cannot penetrate deeply into biological molecules
-causes the formation of cross-linked pyrimidine dimers
-thymine dimers may cause mutations when that DNA strand is replicated
73
Ultra-Violet Radiation
Effective mutagen
-creates pyrimidine dimers that distort DNA conformation in such a way that errors tend to e introduced during DNA replication
74
Defective Excision Repair: Xeroderma Pigmentosum
Inherited disease (autosomal recessive)
-associated with mutations in at least 7 genes encoding proteins involved in the nucleotide excision repair systems
-extreme sunlight sensitivity (UV radiation) development of skin cancers and other severe conditions
75
How to repair damaged DNA
4 types
-Base excision repair (BER)
-Nucleotide excision repair (NER)
-Mismatch excision repair (post dna rep)
-Proofreading by DNA polymerase (during dna rep)
76
Base Excision Repair (BER)
Prior to DNA replication
-corrects damage caused by
*Oxidation
*Deamination
*Alkylation
-these base legions can be spontaneous or induced
77
Nucleotide Excisions Repair (NER)
Prior to DNA replication
-corrects DNA damage caused by UV induced pyrimidine dimers
78
BER steps
Recognition of erroneous base by DNA glycosylase
-Cutting of DNA backbone by AP endonuclease
Example: Uracil is noncomplementary
1. uracil DNA glycosylase recognizes and excises incorrect base
2. AP endonuclease recognizes lesion and nicks DNA strand
3. DNA polymerase and DNA ligase fills gap
4. Mismatch repair
79
NER
Mechanism to correct DNA damage caused by UV induced pyrimidine dimers
1. region with dimer is cut out
2. gap filled by dna polymerase fragments are joined by ligase
80
Mismatch Excision Repair in Human Cells
Errors after proofreading
1. Removal of mutations by nuclease
2. Gap filled by DNA polymerase
3. Sealing nick by DNA ligase
81
Differential Gene Expression
Basis for development, cellular differential and physiological cellular responses
-expression of gene can be controlled on different levels
82
Transcription Control
The most common regulatory mechanism of gene expression
83
Transcription & Translation in Prokaryotic Cells
Coupled both spatially and temporally (space and time)
-b/c Prokaryotes have no defined nucleus transcription and translation happen in the cytoplasm and both happen at the same time
-a newly synthesized mRNA is immediately complexed to ribosomes and protein synthesis begins
84
Gene Expression in Prokaryotes
Genes are clustered into regulatory units
-structural genes for enzymes that carry out a sequence of related reactions and are found together in the same regulatory region
-regulatory units are transcribed into a single polycistronic mRNA
85
Cistron
Another name for a gene
86
Prokaryotic Regulation on gene expression due to environmental changes
Gene expression studies a lot on E. Coli
-Enzymes could be:
*Inducible (adaptive): lac operon
*Constitutive
*repressible: trp operon
-Regulation maybe under positive or negative control
87
Preferred Carbon source for bacteria
Glucose
88
Lac Operon
Transcribes only if...
- no glucose is available
- lactose is present
89
Regulatory Elements
Almost always located upstream of the gene cluster they control and are cis-acting
-lac operon
90
Molecules that bind to cis-acting site
Are trans-acting elements
-lac repressor protein
-trans binds to cis
91
Lac Operon Control
-Negative control
-Enzyme Induction
-I^- Mutation
-O^c Mutation
-I^s Mutation
92
Negative Control of lac operon
Wild type
-no lactose present: repressed
-repressor binds to operator, block transcription
-no transcription = no enzyme
93
Enzyme Induction
Lactose present: Induced
- No binding occurs: transcription proceeds
-operator-binding region is altered when bound to lactose
-transcription = translation = enzymes produced
-lac repressor undergoes allosteric change-> allosteric protein
-in this example enzyme induction results from a relief of repression
94
I- Mutaion
Mutant Repressor gene
-no lactose present: Constitutive
-operator binding region of repressor is altered
-no binding occurs: transcription proceeds = enzyme produced
95
O^c Mutations
Mutant Operator Gene
-no lactose present: Constitutive
-nucleotide sequence of operator gene is altered: no binding occurs
-transcription proceeds = enzyme produced
96
I^s Mutation
Mutant Repressor gene
- lactose present: repressed
- lactose binding region is altered, no binding to lactose
-repressor always bound to operator, blocking transcription = no enzyme produced
97
Catabolite-activation protein (CAPs)
Involved in repressing expression of lac operon when glucose is present
-Inhibition: Catbolite repression
98
In Absence of Glucose
cAMP levels increase
-results in formation of a CAP-cAMP complex
-this binds to CAP site of promoter
-stimulates transcription
-positive control
99
In Presence of Glucose
cAMP levels decrease
-CAP-cAMP complexes are not formed
-transcription is not stimulated
100
Gene Expression in an Operon
May be..
-Inducible (adaptive)
-Constitutive
-Repressor (trp operon)
-positive or negative control
101
A Repressible Gene System
The enzyme for Tryptophan production form an operon
-in presence of tryptophan: operon is repressed
-tryptophan acts as a co-repressor
102
Summary of Repressible Gene System
-The tryptophan (trp) operon in E. Coli is a repressible gene system
-trp operon is activated in the absence of trp
-trp operon is repressed in the presence of trp
103
Summary of Absence and Presence of Glucose
Absense: stimulates transcription
Presence: does not stimulate transcription
104
Inducible Gene Expression
Turned on when signal molecule is present
-lac operon
105
Constitutive Gene Expression
Always "on"
106
Repressible Gene Expression
Turned off when signal molecule is present
-trp operon
107
Negative Control of Regulation
Expression is normally blocked by teh repressor
-the inducer: repressed control of the lac operon
-the repressor: compression control of the trp
operon
108
Positive Control of Regulation
Expression requires the positive signal of the activator CAP_cAMP bound to the CAP site
-the CAP-cAMP system of the lac operon
109
Transcription in Eukaryotes
Occurs in nucleus
-not coupled to translation
-requires chromatin remoldeling
110
Gene Regulation in Eukaryotes
More complex than in prok bc of:
- larger amount of DNA
- large # of chromosomes
-DNA is associated w/ proteins in the form of chromatin
- spatial seperation of transcription and translation (in nucleus-cytoplasm, respectively)
- mRNA processing
- RNA stability
- cellular differentiation in eukaryotes
111
Differential Gene Expression
Basis for:
- development
- cellular differentiation
- physiological cellular responses
112
Expression of a Gene
Can be controlled on 6 different levels
1. Transcriptional control
2. RNA processing control (alternative splicing)
3. RNA transport and localization control
4. Translation control
5. mRNA degradation control
6. protein activity control
113
Eukaryotic Benefits of Gene Regulation
Can respond to
-changes in nutrient availability
-environmental changes
114
Plant and Animal Multicellularity
Are multicellular
-more complex cell structure
- much greater level of gene expression
115
Gene regulation is necessary to ensure
Temporal and Spatial expression
1. Gene expressed in pattern during various developmental life stages
- some only expressed in embryonic and some only expressed in adulthood
2. differences among distinct cell types
- nerve and muscle cells look different b/c of gene expression not DNA content
116
Chromatin Structure
3D packing of chromatin affects gene expression
- 2 conformations: Closed Conformation, Open Conformation
117
Closed Conformation (Chromatin Structure)
Tightly packed
- transcription may be difficult or impossible
118
Open Conformation (Chromatin Structure)
Highly extended
- transcription can take place
119
Chromatin Remodeling
2 common ways chromatin structure is altered
- Covalent Modification of histones
- ATP-Dependent Chromatin Remodeling
120
Covalent Modification of Histones (Chromatin Remodeling)
Histones (that form nucleosomes) and post-transcriptional modifications
- creates opening and closing of chromatin structure
*amino terminals of histones are modified in various ways
- acetylation, phosphorylation, methylation
- histone acetyltransferase (HAT)
- histone deacetylase (HDAC)
121
Histone Acetyltransferase (Chromatin Remodeling: Covalent Modification of Histones)
- aka HAT
Adds acetyl groups
- lossens interactions between histones and DNA
- mediates effects of activators
122
Histone Deacetylase (Chromatin Remodeling: Covalent Modification of Histones)
- aka HDAC
Removes acetyl groups
- tightens interaction between histones and DNA
- mediates effects of repressors
123
ATP- dependent Chromatin Remodeling
SWI/ SNF is one of the best studied chromatin remodeling complexes
- repositioning of nucleosomes
- allows for different chromosomal regions to be accessible to transcription proteins
124
DNA Methylation
Associated w/ decreased gene expression
- acts as a mechanism for gene silencing: prevents binding of regulatory factors, and by affecting chromatin status
- adds methyl group to cytosine w/in C-G dinucleotides (often located in regulatory regions of genes)
125
Core promoters
Minimum part of promoter needed for accurate initiation of transcription (by RNA P II)
- 80 bp long
2 types
- Focused Core Promoters
- Dispersed Core Promoters
126
Focused Core Promoter
Specify transcription initiation at a single specific start site
- short nucleotide sequences bound by a specific regulatory factors
-serves as a platform for assembly of RNA P II
Important components
- Inr (initiator element)
- TATA box (TA rich sequence)
- BRE (TFIIB recognition element)
- MTE (motif ten element)
- DPE (downstream promoter elements)
127
Dispersed Core Promoters
Direct initiation from several weak transcription start sites
128
More About Focused Promoters
* Regulatory/ control elements
- affect binding of RNA polymerase to the promoter
- DNA sequences bound by transcription factors
* Can be proximal to the promoter
- vary location
- but often found in100 to 200 region
* Can be distal to the promoter
- enhancers: stimulate transcription (can do from long distance)
- silencers: inhibit transcription (can also do from long distance)
129
Regulatory Transcription Factors
Proteins that influence ability of RNA polymerase to transcribe a given gene
2 Main Types
- General Transcription Factors
- Regulatory Transcription Factors
130
General Transcription Factors
Required for
- binding RNA polymerase to core promoter
-progression to elongation stage
- are necessary for basal transcription
131
Regulatory Transcription Factors (Specific)
Regulate rate of transcription of nearby genes
- influence ability of RNA polymerase to begin transcription of a particular gene
132
Elements Found in Focused Promoters
-Distance Enhancer
- Proximal Promoter
- Core Promoter
- Termination Sequence
- Coding Region
133
Regulatory Transcription Factors recognize...
Cis regulatory elements located near core promoter
- sequences known as: response elements, control elements or regulatory elements
134
Binding of these proteins...
Affects transcription of an associated gene
- Activator: regulatory protein that increases the rate of transcription is termed an activator
*enhancer: sequence it binds to
- Repressor: regulatory protein that decreases the rate of transcription
*silencer: sequence it binds to
135
Promoters
Nucleotide Sequences
- serves as recognition sites for transcription machinery
includes
- TATA box
- proximal sequences (GC, CAAT and more)
- enhancers and silencers
136
TATA Box (TATA A/T AAR)
Region RNA Polymerase binds to
TATA A/T AAR (R is any purine)
137
Transcription Factors
Transcription Regulatory Proteins
- target cis-acting sites of gene regulation expression
- may be modulated by : phosphorylation or coactivator binding
138
Human Metallothionein IIA gene (hMTIIA)
Example of how genes can be transcriptionally regulated through promoters, enhancers and transcription factors
139
Functional domains of Transcription Factors
Proteins that serve as transcription factors have two domains
- Trans- activating or repressing domains
- DNA Binding Domain
140
Trans Activation or Repressing Domain
Trans- activating domain- activates
Trans- repressing domain- represses transcription through protein-protein interactions
141
DNA Binding Domain
Directs binding of the protein to a specific sequence of DNA
*helix-turn-helix
*zinc fingers
*basic leucine zippers (bZIP)
142
TFIID
Transcriptional activator recruits TFIID to the core promoter and/or activates its function
-thus transcription will be activated
143
Enhancers
Enhances transcriptional activity from a distance
- acts independent of orientation
144
Silencers
Confers stage-and tissue-specificity of expression
-acts independent of position
-properties are similar to enhancer but it silences gene expression
145
Enhancesome
forms when activators bind to enhancers
-interacts with transcription complex
146
General Transcription Factors
Required for the binding of RNA polymerase II to the promoter
147
TFIID
The first general transcription factor to bind the promoter, binds to the TATA box through the TATA binding protein (TBP)
148
Most regulatory transcription factors...
do not bind directly to RNA polymerase
149
TFIID and Mediator
Common protein complexes
-communicate the effects of regulatory transcription factors to RNA pol II
150
Alternative Splicing
Pre-mRNA can be sliced in more than one way
- produces two alternative versions of a protein that have similar functions (b/c much of their amino acid sequences are identical
- there are still enough difference in the amino acids to give each protein its own characteristics/ function
151
a-Tropomyosin (Alternative Splicing Example)
Protein Function: regulation of cell contraction
*Is found in
-Smooth muscle cells (uterus and small intestine)
-Striated muscle cells (cardiac and skeletal muscle)
152
Alternative Spicing Process
Spliceosome recognizes the 5' and 3' splice sites and removes the intervening intron
- Alternative splicing is the primary mechanism for resulting mRNA processing
- not a random event: specific splicing pattern depends on the cell
153
Splicing Factors
Modulate the ability of spliceosomes to recognize or choose the splice sites
- splicing repressors and activators play a key role in the choice of splice sites
154
Dscam Gene mRNA
The combination of exons resulting from alternative splicing can result in over 38,000 versions of DSCAM protein
155
Drosophila Sex Determination
Sex lethal (Sxl) and transformer (tra) and doublesex (dsx) genes help regulate for sex determination
- Sxl gene: acts as a switch that selects sexual development pathway by controlling splicing of Dsx transcript in a female-specific fashion
156
mRNA Stability
Stability of Eukaryote mRNA varies greatly
- stability of mRNA can be regulated to its half-life (shortened or lengthened), influences mRNA concentration and gene expression
- factors that affect stability
1. length of poly A tail
2. destabilizing elements
157
Pathways for degradation of euk mRNA
- decapping pathway: attacks caps of mRNA, removal of cap
- deadenylating: removal of poly A tail
- endonucleolytic cleavage: attacks mRNA from middle of mRNA sequence, cuts the middle of sequence
158
RNA Silencing
RNA induced gene silencing
- affects transtability or mRNA
- small antisense RNA on/affects specific regions of mRNA
- can also repress transcription by altering chromatin
-microRNA (miRNA)
159
microRNA (miRNA)
Short (21-24 nt)
- double-stranded RNA
- involved in RNA silencing
- encoded in nuclear genome and transcribed by RNA pol III
- sections of miRNA gets loaded into RISC or RITS
RISC: degradation of mRNA, translation inhibitation
RITS: nuclear genome silencing
-mutants w/out normal miRNA function show developmental defeats
160
Protein modification and degradation
Can affect ____ of proteins
- location
- structure
- function
- activity
- interactions
161
Ubiquitin- mediated protein degradation
Recognizes substrate protein and catalyzes the addition of Ub (76 amino acid protein)
- Ub are recognized by proteasome and the protein will get cleaved into small peptides
- protein will be degraded and recycled
