Exam 1 Flashcards
Crohn’s Disease, Alcohol and celiac disease damage intestinal mucosa and inhibit the absorption of what?
Folate
Three inhibitors of FH4 synthesis
5-fluorouracil stops dUMP to dTMP
Trimethoprim mimics folic acid and binds to FH2 reductase
Methotrexate looks like FH2 and binds FH2 reductase and inhibits
How is B12 absorbed in the GI?
B12 bound to R-binders (haptocorrins) because its not stable in the GI, sometimes its bound to meat so thats okay, but supplements are bound to R-binders to protect it
Stomach makes intrinsic factor via gastric mucosa- R-binders are degraded and B12 bound to intrinsic factor secreted by parietal cells
Intrinsic factor binds receptor in small intestine is absorbed- complexes with transcobalamin II before entering ciruculation- half sotred in liver and half sent to other tissues
Schilling test stages and corresponding diseases
Stage 1: Radiolabeled B12, shows dietary deficiency
Stage 2: Radiolabeled B12 and intrinsic factor, shows pernicious anemia
Stage 3: B12 and antibiotics shows bacterial infection
Stage 4: B12 and Pancreatic enzymes show malabsorption due to pancreatitis
Hyperhomocysteniemia
High homocysteine from problems with B12, folic acid or PLP- different products accumulate depending on the problem
Homocysteine degraded or made into cysteine
PLP deficiency will hit limit on SAM making and end up with homocysteine build up
Methyl Trap Hypothesis
Folate gets stuck in methyl form- stuck in useless form, and leads to a lot of problems
If you dont have the B12 to convert the homocysteine to methionine using the methyl folate, you get all your folate stuck in methyl form and B12 is the only reaction that uses methyl folate so it becomes useless
Neural Tube Defects
Folate deficiency in pregnancy is risk factor for neural tube defects
Folate deficiency leads to inhibition of DNA synthesis (necessary for purine syn)
High homocysteine is sign of folate deficiency
Take folate supplements
Megaloblastic Anemia
Decreased synthesis of thymine and purine bases- limits DNA synthesis
Causes RBCs to become large and RBCs wont function properly
Jean Ann Tonich has MGBA- if homocysteine and methylmalonyl CoA are both high=B12
if homocysteine only high=folate
Pernicious Anemia
Deficiency of intrinsic factor; binds B12 receptors in small intestine and is absorbed
Treat with IV shots of B12- cant absorb supplements
Lesch-Nyhan Syndrome
Defective hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
Basically purines arent salvaged and are instead converted to uric acid
PRPP is substrate of salvage, if HGPRT is deficient, then PRPP will accumulate- this stimulates purine synthesis which leads to purine degradation
Adenosine Deaminase Deficiency (ADA deficiency)
Severe immune problems- lymphocytes use salvage pathway
Body cant make T or B cells- cant get rid of waste, toxics build up and destroy B/T cells= SCID
Gout: Lotta Topaigne
Uric acid normally excreted in urine
Excess uric acid= gout
90% due to excretion issues, and 10% due to overproduction
Xanthine oxidase inhibition prevents uric acid production- use Allopurinol to treat, its a suicide inhibitor of xanthine oxidase
Commonly in big toe
Best choice to tag is glycine- gets the whole molecule as it contributes both C and N
With an undersecretion; we wont see labeled substrate in urine
with an overproduction: will see labeled substrate in urine
Orotic Aciduria
Two deficient enzymes- Orotate phosphoribosyl transferase and orotidine 5’-decarboxylase
both of these are part of pyrimidine synthesis pathway to make UP
Orotic acid excreted in urine, treat with oral uridine
Patient will show problems with growth b/c pyrimidines arent being made
What is the dominant form of DNA in living systems
B DNA
Differences bw DNA and RNA
RNA for expression of info and not as stable, uses ribose and has U instead of T, but it also has glycosidic bonds, but does break up in basic solution (the OH makes it less stable) unlike DNA, which is stable in base
Prokaryotic Ribosomal subunits and RNA
50s+30s=70s
3 Types of RNA= 23,16,5s
Eukaryotic Ribosomal subunits and RNA
40s+60s=80s
4 Types of RNA=28,18,5.8,5s
Mitochondrial ribosomes are 55s and similar to prokaryotes
Tm=?
Tm= 69.3+0.41*(%G+C)
G:C melts slower than A:T b/c of 3 H bonds
Ivy Sharer; HIV patient treat with Zidovudine (ZDV) How does it work?
Slows HIV progression in patients; attaches to 3’OH, azide doesn’t allow reverse transcriptase to add to 3’ so it cannot work- stops replication of your own genes too- bad side effects
Colin Tuma: Tumor patient; uses 5-Fluorouracil
5-FU inhibits production of deoxythymidine- analog of uracil or thymine- inhibits thymidylate synthase so no thymine is synthesized
Lack of thymine slows tumor cell progression
Newman Itis- bacterial infection
Azithromycin and ciprofloxacin
Azithromycin binds 50S subunit of ribosomes and stops protein synthesis- this is specific to prokaryotes because eukaryotes dont have 50S
Mitochondrial ribosomes are similar to bacterial, so mitochondrial protein synthesis inhibition can be a side effect
Ciprofloxacin targets DNA gyrase, which is specific to bacteria
How to Calculate Nucleotide numbers given percent bases?
with 200 bp, where 40% is G and C, and 60% is A and T, 30% of the nucleotides is T, and there are 400 nucleotides, which means 30% of 400 is 120 T
If a sample is 30% G, what is the %A?
30% G means 60% C and G, so 40% A and T, meaning 20% A
Helicase
separates DNA- unzips
Topoisomerase
Cuts DNA backbone because supercoiling makes a mess and untangling is hard, so just cut it
Topo I
Cuts one strand of two
DNA Gyrase (Topo II)
Cuts both strands- target of ciprofloxacin
Single stranded binding proteins
bind cut ends and stop from re-joining before replication.
our bodies also recognize single stranded DNA as foreign and without the binding proteins, the strands would be degraded
DNA Pol (I,II,III)
DNA synthesis- prokaryotes use 3, the third is for actual replication, and others are for other things like repair
Primase
needs 3’OH to start, DNA pol can start without it- primase adds short RNA primers so DNA can start replicating
DNA Ligase
comes in and re-joins nicks and parts not connected
Eukaryotic DNA
Larger genomes, histones/nucleosomes, linear DNA
Prokaryotic DNA polymerases
Pol I: replication, repair, primer excision
Pol II: DNA repair
Pol III: Major replication, has 3’-5’ exonuclease for proofreading
Eukaryotic DNA polymerases
Pol alpha: associated with primase
Pol beta: DNA repair, primer excision
Pol gamma: mitochondrial DNA synthesis
Pol delta: replication, 3’-5’ exonuclease for proofreading- lagging strand
Pol sigma: replication, 3’-5’ exonuclease for proofreading- leading strand
DNA Damage sources
Smoking- benzo(a)pyrene adducts with guanine, can distort DNA
Sun- thymine dimer
X-ray- OH radical
Deamination
BER
base excision repair- removes damaged base that cant be fixed
Glycosylase cleaves glycosidic bond
Dexoyribose cleaved by AP endonuclease
Exonuclease removes several other residues
DNA Pol fills in the gap and Ligase seals nicks
NER
Nucleotide excision repair- fixes large segments like pyrimidine dimer or lesions with bulky substituents
Endonuclease cleaves distorted region and removes DNA
DNA pol fills gap and ligase seals nicks
uses 16 enzymes
Treat HIV
Reverse transcriptase inhibitor
HIV is highly mutagenic so it can overcome treatment- use multiple inhibitors to treat
Smoking Effects
Huge guanine adducts need to be removed by NER
Sun exposure
Thymine dimers, remove with NER
Eukaryotic RNA Polymerases
RNA Pol I: rRNA except 5S
RNA Pol II: mRNA- coding sequence
RNA Pol III: tRNA and other small RNA like 5S rRNA
Polycistronic Genes
some prokaryotic genes
one RNA codes for more than one protein
All proteins part of same metabolic pathway- regulate the whole pathway at once, Lac operon
Cis elements vs Trans factors
Cis element is DNA sequence that can bind to protein factor (DNA itself) like enhancer element and silencer element
Trans factor is protein that can bind to DNA- it can move and its a protein element like repressor protein
RNA polymerase structure
4 subunits, 2 alpha, 1 beta, and 1 beta’
Sigma factor scans DNA for promoter and binds-pol binds sigma
Holoenzyme= with sigma
Apoenzyme= without sigma
Thalassemias
Mutations in patients with beta+ thalassemia is point mutation of T–>C near 3’ end of globin gene (switch pyrimidine to pyrimidine)
Results in no poly A tail= less stable RNA
Changes UGG to UGA= STOP codon leads to truncated protein and severe homozygous phenotype
Rifampin/Rifamycin
Ivy Sharer pt
Prevent transcription INITIATION by binding beta subunit of RNA pol and interfere with formation of initial phosphodiester bond in mRNA
rifampin selectively kills M.tuberculosis, but it may develop resistance, so treat with another drug of different mechanism like isoniazid to decrease mutation advantage
Streptolydigin
Prevents message ELONGATION
Alpha amantin
Inhibits eukaryotic RNA pol II and prevents mRNA synthesis, starts with initial mild GI symptoms and w/in 48 hr massive liver failure
treat with liver transplant or IV milk thistle preparation
What are the 3 STOP codons
UAG
UGA
UAA
What is the START codon
AUG (ATG) codes for methionine
What are the major characteristics of the genetic code?
Degenerate- multiple codons code for same amino acid- 61 codons
Unambiguous- each codon codes for only ONE amino acid
Universal- same in humans, plants, bacteria
Nonoverlapping- each codon is distinct and adjacent to the next codon
Wobble Hypothesis
3’ part of triplet codon can wobble and be different, it base pairs less with the anticodon
some tRNA have inosine instead of other nucleotides allowing it to base pair with multiple bases
Aminoacylation
Aminoacyl-tRNA synthetase attaches AA to terminal A of CCA using ATP to form intermediate
the Carboxyl group on AA is joined to 3’ carbon of A by ester bond
Amino group free to be added to polypeptide chain
Initiation stage of protein synthesis
Components of translatory machinery assembled and met is added
mRNA, met-tRNA, ribosomal subunits, initiation factors (eIF4F made of 4E, 4G, 4A) and GTP
IF3 complexes with small ribosomal subunit
IF2 recognizes tRNA for met and transfers a GTP, tRNA then brought to small ribosome/IF3
mRNA associates with small ribosomal subunit- uses ATP
tRNA binds codon on mRNA- large ribosome subunit joins small- uses GTP
tRNA met put into P site
Elongation stage of protein synthesis
aa added to carboxyl end of growing peptide
EF-Tu (eEF1a-GTP) and EF-Ts (eEF-1b) directs charged tRNA to A site
AA chain transferred to amino acid on A site by peptidyl transferase in P site of large subunit- RIBOZYME
Enzymatic activity associated with large ribosomal subunit
charged tRNA to A site, next to P site tRNA with peptide chain
peptidyl transferase moves chain to A site tRNA and uncharged tRNA moves to E site and leaves
new chain tRNA moves to P site and new tRNA comes to A site
Translocation in protein synthesis
movement of ribosome along mRNA
Needs EF-G (eEF2) and GTP- causes net movement of peptidyl-tRNA from A to P
Uncharged tRNA moved from P to E
Termination of protein synthesis
at first in-frame STOP codon
no tRNA is complementary with stop codon- release factors bind and peptidyl transferase hydrolyzes bond between polypeptide and last tRNA
ribosomal subunits dissociate and release mRNA
Carboxylation
Glutamate- coagulation cascade
Hydroxylation
Proline/lysine- collagen stability (scurvy and osteogenesis imperfecta)
Phosphorylation
Serine, threonine, tyrosine- enzyme activity
Glycosylation
Serine, asparagine- secretion, membrane proteins
Fatty acylation
membrane anchor
Prenylation
membrane anchor
ADP-ribosylation
enzyme activity
Collagen Assembly
procollagen post translationally modified by hydroxylation of proline and lysine
glycosylation
triple helix forms and stabilized by h-bonds from hydroxyproline and hydroxylysine residues
Osteogenesis imperfecta
defects in collagen assembly/stability from missense mutations or defective post translational modification
Protein Targeting
proteins for secretion, membrane, and organelles modified in ER and golgi
targeted to ER by signal peptide- Signal recognition particle (SRP)- docks with receptor on ER, protein enters ER via pore and then modified and enters secretion
I-Cell disease
I-cell disease is lack of phosphotransferase activity- missing mannose-6-P signal for lysosome- proteins will leak out of cell and lysosome fill with inclusion bodies
Streptomycin
Bind 16S rRNA of 30S and inhibits translation initiation
Tetracyclin
Bind 30S ribosomal subunit and block aminoacyl-tRNA to A site of ribosome
Chloramphenicol
Bind 50S ribosomal subunit block peptidyltransferase activity and stops binding of AA to tRNA
toxic, inhibits mitochondrial activity too
Erythromycin
Bind 50S ribosomal subunit and prevents translocation from A to P site
What is Cancer?
Loss of regulation of cell cycle
leads to frequent aneuploidy- irregular chromosome number
Cells continue to divide- not always faster, just unregulated
What causes cancer?
Mutations leading to uncontrolled proliferation
Come from ionizing/UV radiation, chemicals, spontaneous
Most mutations detected and corrected
Some mutations cause the uncontrolled growth- dangerous with metastasis
BRCA-1,2
Breast, ovarian and prostate cancer
Repair by homologous recombination
Cancer Overview
Mutations in multiple genes leading to malignant transformation of normal cells
infinite proliferation, anchorage independent, resist growth inhibition and apoptosis, de-differentiation, metastasis
Lung cancer development
Develops slowly, smoking increases the incidence of lung cancer with a lag of 20 years
Oncogene
Gain of function mutation in growth promoting gene
Proto oncogene
Corresponding normal gene to oncogene
Tumor Suppressor Gene
normal genes coding for growth inhibition
loss of function mutation in cancer- unregulated cell growth
Oncogene Virus theory
RNA tumor virus carry oncogene and usually integrate into host DNA- likely that cellular protooncogene picked up when provirus genome transcribed into viral RNA and packaged into virus particles
Proto oncogene mutated into oncogene- v-onc, found a corresponding c-onc proto oncogene for each v-onc
transform normal cell into tumor cell- oncogene drive cell cycle forward
c-Jun and c-myc active around G0/G1 division transcribe genes that force cell out of G0
Cell Cycle Regulation
Highly regulated at G0 and G1/S check points
Activated by growth factors and hormones that control via cyclin and CDKs (ABDE- match with specific CDKs to form complex that allow cell to progress to next stage)
Cyclin-CDKs regulated by phosphorylation or CKI (CDK inhibitor)
Proto oncogene conversion to oncogene
Radiation or chemical mutation (coding region=translation, promoter region=gene expression)
Gene rearrangement: put proto oncogene under strong transcription activator (Burkitts), or fuse with another protein making hyperactive (CML)
Gene amplification: increase production of gene- make many copies (neuroblastoma)
Ras and Cancer
Ras is G-protein involved in mediating cell growth/mitosis
MAP kinase pathway activates transcription of myc and fos and phosphorylates AP-1 (heterodimer of fos and jun)
MAP kinase pathway activates myc, fos, and jun (all proto oncogenes) that lead to cell signaling repsonse to activated Ras leading to continuous mitosis
Ras pathway
Ras is an oncogene- GOF=Cancer
Growth factor bind ras- ras bind GTP= active, slowly hydrolyses GTP to turn off
Active ras activates MAP kinase cascade- activation of nuclear proteins that activate transcription and activates cell cycle
Ras mutations blocks GTPase activity and makes it active all the time leading to constant MAP kinase stimulation and constant mitosis
NF-1
Neurofibromin activates Ras GTPase- its a tumor suppressor
LOF=Neurofibromatosis
Retinoblastoma (Rb-1)
Tumor suppressor gene
Negative regulator of cell cycle, arrests it in G1 phase- stopping inappropriate cell proliferation
Rb binds to transcription factors E2F1
unphosphorylated in G0 and G1, and multiply phos in S, G2/M- releases binding factors that allow gene replication
Rb Pathway
Binds and inactivates E2F- which initiates G1/S cell cycle transition (Rb controls crucial cell cycle checkpoint)
Rb hypo or hyperphosphorylated (hypo=binds E2F and inhibits, hyper=releases E2F and activates)
Rb Phosphorylation control
Growth factor binds receptor and initiates Ras/Raf signal pathway causing induction of Cyclin D which binds CDK4, causing Rb to become hyperphos, releasing E2F
4 Key regulators of Cell cycle
Rb: E2F release upon hyperphos
CDK4: hyperphos Rb
P16/INK4: code for CKI and block Rb phos
Cyclin D: Bind CDK to cause Rb phos
Rb Mutations
De novo= UV radiation to eye- clear lens susceptible, and replicates a lot
One mutation is okay, because other allele is fine, two mutations is rare
Inherited= Combo of inherited mutant allele with de novo mutation in other allele is bad- 100% chance retinoblastoma
p53 functions
Senses DNA damage and does 3 things
- Halts cell cycle- new DNA synthesis wont replicate damaged DNA
- Up-reg genes for DNA repair
- Severe damage- stimulates apoptosis
Li Fraumeni Syndrome
Genetic defect in p53- leads to high frequency of cancer
see patient present with cancer, and family history shows cancer in lots of family members- different cancers b/c p53 - most cancers have mutation in p53 as it progresses
p27
inhibits cyclin and CDK, blocking entry into S phase
breast cancer prognosis determined by p27 levels
reduced levels of p27= poor outcome for breast cancer patients
Patched, Smoothened, Sonic Hedgehog
How tumor suppressor genes and oncogenes work together
Patched inhibits smoothened from starting transcription, patched is the receptor for SHH, when SHH is bound, patched stops inhibiting smoothened so transcription happens
Smoothened is proto oncogene
Patched is tumor suppressor
Activation of Caspases by
TNF (tumor necrosis factor) binding death receptor
Cytochrome c from mitochondria
Death receptors
Fas/CD95
TNF-R1
Death receptor 3 (DR3)
activated receptor binds initiator caspases 8 and 10 which activate execution caspases 3,6,7
CML Philadelphia Chromosome
translocation of long arms of 9 and 22- rearrangement leads to philadelphia chromosome and Chronic myelogenous leukemia
Abl is TK (proto oncogene) and when fused with bcr its always active
Abl
TK proto oncogene
able from 9 fused with bcr on 22 resulting in constitutive activation of abl
bcr constitutively active on leukocytes with abl gene on it, so abl also constitutive leading to cell proliferation as abl activates ras pathway
Burkitt’s Lymphoma
c-myc gene translocated to be controlled by promoter for ig heavy chain gene- c-myc synthesized at high levels leading to proliferation of wbcs
DNA replication treatments
Anti folates methotrexate target thymidylate synthase stop purine synthesis
Base analogs 5-fluorouracil target thymidylate synthase
alkylating agents damage DNA cyclophosphamide and cisplatin
ionizing radiation damage DNA
vinblastine- MT Depol
Taxo- MT pol
inhibit mitosis
Avastin-block VEGF- choke blood supply
Monoclonal antibodies- Hercpetin against Her2 to slow growth
Active site inhibitor Gleevec imatinib bind bcr abl TK and inactivate
Trp attenuation
Transcription in prokaryotes regulated by attenuation, when trp is high, transcription happens fast and there are lots of trp codons in the beginning so translation happens fast and causes the RNA to fold on itself and form a hairpin loop and this is a termination signal for RNA pol
when trp is low, the ribosomes stall at trps in the beginning b/c it doesnt have enough trp, so a different hairpin loop forms and does not cause termination, so the whole mRNA is transcribed
What is the requirement for attenuation regulation?
Transcription and translation MUST be coupled, so it DOES NOT WORK in eukaryotes
7 Regulations of Eukaryotic gene expression
DNA and chromosome Transcription Transcript processing RNA transport and localization Initiation of translation Stability of mRNA Stability of protein
Chromatin remodeling
ATP driven- use ATP to unwind sections of DNA from nucleosomes
Acetylation- covalent modification of histone tails, transfer acetyl group to lysine and remove positive charge resulting in reduced electrostatic interaction with negative DNA making it easier to unwind DNA
DNA Methylation
Cytosine in DNA methylated to make 5-methylcytosine in GC-rich islands (CpG islands)
near/in promoter- can activate or repress
Prader WIlli and Angelman
Male and female methylate differently- chrom 15
Prader willi inherited from father; paternal gone so maternal 1,3 expressed b/c 2 is methylated
angelman inherited from mother; maternal gone so paternal 2,3 expressed b/c 1 is methylated
VDJ Recombination
Done in immunoglobulin and t-cell receptor genes
recombine variable regions- large number of combinations
DNA spliced like mRNA- permanent change
Nearly randomly combines variable, diverse, and joining regions and diversely encodes proteins to match antigens from bacteria, viruses, parasites, etc
Gene Amplification
regions of chromosome repeated cycles of DNA replication- new DNA excised into small double minutes
double minutes integrate into other chromosomes- amplifying gene in process
methotrexate: inhibits cell prolif by inhibiting dihydrofolate reductase- formation of FH4 for purine synthesis
Gene deletions/ translocations
unnoticed without disease
CML- philadelphia chromosome
Burkitts lymphoma
Triple Repeat Expansion
Fragile X- CGG triplet amplified
Huntington Disease- CAG repeat in coding region
Androgen insensitivity
Pts make androgens but target cells fail to respond because they lack the appropriate intracellular transcription factor receptors
Thyroid Hormone receptor disorder
Thyroxine important to brain development
Hypothyroidism increased T3 or Increase TSH
abnormalities in cardiac fxn, deafness, early death in knockout mice
Zinc Finger
Estrogen receptor
One zinc, 4 cysteine
Alpha helix with NRS that binds to specific sequence in major groove of DNA
Leucine Zipper
alpha helix 30-40 aa with leucine every 7 aa, homo or heterodimer, coded by fos and jun
Helix-turn-helix
one helix fits into major groove of DNA and stable in binding without DIMERIZATION
Helix-loop-helix
Transcription factor also function as dimer (homo/hetero) myogenin in skeletal muscle- involved in cell differentiation
Regulation of PEPCK
stimulated by glucagon, glucocorticoids and thyroid hormone; imp for gluconeogenesis
inhibited by insulin
Alternative Splicing/Poly A
Splicing of single primary transcript makes 2 different mRNAs because of upstream and downstream Poly A signals- do the first one, then splice it out and use the second one
Retrovirus Gene therapy
Adv: enters cell efficiently, integrates stably into host genome (targets only dividing cell)
Disadv: limit insert size 8-12kb, integrates into host genome
Adenovirus gene therapy
Adv: enter cell efficiently div and non div, high expression of insert doesnt integrate into host
Disadv: serious immune response, doesnt integrate into host
Adeno-associated virus gene therapy
Adv: enter efficiently div and non div, little or no immune response, integrates at specific site chrom 19
Disadv: limit insert size 5kb, difficult to produce
Herpes Simplex Virus gene therapy
Adv: carry up to 20kb, prolonged activity, infects nerve cells very efficiently*
Disadv: can cause immune response
Liposomes gene therapy
Adv: accept large inserts, no immune response
Disadv: inefficient cell entry, no integration into host, can be toxic
Nake DNA gene therapy
Adv: accept large inserts, no immune response
Disadv: very inefficient entry, no integration into host genome
Most common used vectors in gene therapy
Adenovirus, retrovirus, naked/plasmid DNA
most commonly used to address cancer diseases
Success with human gene therapy
SCID Malignant Melanoma Leber's congenital amaurosis Hemophilia B Chronic lymphocytic leukemia Chronic myelogenous leykemia Parkinson Disease Cystic fibrosis Retinitis pigmentosa
Glybera
Treat LPL deficiency in Europe
Uses adeno-associated virus to deliver LPL and is a one time IM injection
Four genetic disorders
Chromosome disorders- down syndrome
Single Gene disorder- cystic fibrosis, hemophilia A
Multifactorial disorder- diabetes, heart disease
Mitochondrial disorders- LHON, MERRF
Cryptic site
less efficient splice site, that can become activated if a mutation appears in the normal splice site making the cryptic site a better one- can result in deletion, insertion or even frameshift
cryptic mutated to activity can compete with normal making two mRNA and 2 proteins (can become a better splice site)
Exon skipping
when no alternative sites present, may find another acceptor site- if acceptor site is mutated, may cut out the whole exon as well as the intron- lose amino acids and possible frameshift
Lidocane test
people with multiple genes may have excess protein for metabolism of lidocane- make sure they are numb first
N-acetyltransferase
some people have duplication 10-12 copies in row, much higher enzyme activity, metabolize certain drug classes faster
Structural Hemoglobin Mutation
Sickle cell anemia Glutamate6 to Valine
sickle shaped cells that get stuck in capillaries and have shorter life span- anemia
biconcave- cant squeeze through capillaries and can cause local infarcts and pain
Due to low oxygen tension- cause polymerization of HbS- all due to single base change
Expression Hemoglobin Mutation
Thalassemias- over production of one of the subunits, causing homotetramers to form and they dont work so well so they precipitate out and damage membranes and cause RBC loss, also can do splenomegaly. Normally alpha2beta2 tetramers closely balanced
Hereditary persistence of fetal hemoglobin- fetal hemoglobin production doesnt turn off so you get lots of it later in life
Ionizing radiation
create reactive radicals, react with bases
cause double stranded breaks
Nonionizing radiation
shift electrons to higher orbits making reactions more likely
pyrimidine dimers form UV light
Chemicals
base analogs insert, react, change- look like normal bases like bromouracil
deamination converts C to U by removing an amino group from C makes it U
NITROSAMINES cause this
Hot Spots
Human CpG dimers usually methylated but deaminate the methyl C, it becomes a T
since the strand is methylated, repair mechanisms cant determine which base is changed
Xeoderma Pigmentosum
Defective NER- cant repair the pyrimidine dimers
UV causes mutations in the skin cells- start as freckles and turn to lesions
Several related disorders of DNA repair- other repair systems can be mutated
Polymorphism
Multiple forms with frequency greater than 1% with no deleterious effects
Blood groups: ABO system, A and B are antigens, O lacks antigen
codominant is AB- hemolytic reaction to mismatched transfusion
develop antibodies against blood groups we don’t have
Fetal erythroblastosis
maternal rejection of fetal Rh proteins
Rh- lacks antigen or antibody unless exposed
Rh incompatibility, Rh- mother with prior Rh+ baby may be immune now, so later Rh+ babies will be at risk
Hardy Weinberg Rule
Gene frequency in population is important- risk of carriers mating
HW rule for randomly mating large populations- estimate frequency of gene variants
p^2+2pq+q^2=1
Founder Effect
Small numbers large effects
Very few founders- may mean frequencies dont reflect larger population
Start at different place follow different path, end up elsewhere
Multiplication Rule
Probability of multiple events happening together
multiply the risks to get overall risk
Addition Rule
Probability that either one or another of multiple evens occurring
add risks together to overall risk
all add up to 1
Autosomal Dominant
Affects every generation- NO SKIP
One parent affected- source of gene
Father-son transmission happens- not x-linked or mitochondrial
1/2 children will be affected
Autosomal Dominant Diseases
Retinoblastoma
Postaxial polydactyly
Achondroplasia
Autosomal Recessive inheritance
Can SKIP
Not sex linked and 1/4 children affected
Consanguinity can be a factor- increases chance of inheriting mutant gene from same ancestor
Autosomal Recessive Diseases
Albinism
Cystic Fibrosis
Cystic Fibrosis
Disrupt chloride transport
affect pancreatic secretions due to clogging ducts
lungs affected by thick secretions- cant clear material
excess Cl in sweat is DEFINITIVE TEST for CF
New Mutation
inheritance pattern shows no other individuals affected when they would be likely
parentage of child is confirmed and shows no evidence of carrying mutation
Germline Mosaicism
Mutation happens in one of many cells
In a few or many germ cells- autosomal dominant or x-linked disorders appear in unlikely pedigrees in odd proportions
eliminate new mutation if more than one child has an autosomal dominant or x linked disease with no family history of it
osteogenesis imperfecta
Delayed age of onset
some disorders not evident until adulthood
Reduced penetrance
phenotype mild to non existent in some individuals b/c of modifying genes
may affect children much more severely
Age dependent penetration
combination of delayed onset and reduced penetrence
Variable expression
many disorders have descriptions allowing for variability
presence of 3/5 different anomalies diagnostic
severity depends on expression
modifying genes limit expression and appear unaffected
Neurofibromatosis
Autosomal dominant defect in NF-1 protein
Binds to ras and causes constitutive activity
some only get a few skin lesions, others get very large tumors
cafe au lait spots
Pleiotropy
Multiple effects from one mutation
single gene affecting multiple tissues
DNA transcription factors- used by several tissues
Extracellular matrix proteins- expressed at different levels in different tissues
Marfan syndrome
Allelic heterogeneity
multiple mutant forms, different effects, same gene
hemoglobin, sickle cell, beta thalassemia
Locus heterogeneity
multiple genes affect one pathway
similar disorders but different genetics- screen multiple genes to figure out defect
4/5 urea cycle disorders
Anticipation
some dominant disorders more severe in later generations
age delayed disorders occur earlier in succeeding generations
Repeat expansion
Short sequence of direct repeats in gene
soem repeated codons
during meiosis the repeats get longer
some threshold number of repeats causes disease
greater number can cause earlier and/or more severe disorder
not all part of protein sequence
Repeat expansion diseases
Huntington Disease- CAG repeats
Fragile X- CGG repeats
Myotonic Dystrophy
