MCP 1 Flashcards
what is biochemical genetics
genetic branch that deals with inborn errors of metabolism which are single enzyme defects that produce a metabolic block by accumulation of substrate and/or deficiency of products
e.g., PKU
Phenylketonuria (PKU)
defect of PAH enzyme; no phenylalanine–>tyrosine, accumulation of phenylalanine can be fatal; treat with restrictive diet
- Varient PKU: moderate severity
- Non-PKU: least severe
- *example of phenotypic heterogeneity: 3 distinct phenotypes from single gene mutation
Tetrahydrobiopterin (BH4)
defect of cofactor for conversion of phenylalanine–>tyrosine
**example of locus heterogeneity: same clinical phenotype as PKU but mutation in a different gene
major differences between spermatogenesis and oogenesis
- continual production of 1˚ spermatocytes vs. all present at birth
- continual production of spermatids vs. monthly
- 1˚ sperm. produces 4 spermatids vs. 1˚ oocyte produces 1 ovum
- completes meiosis II vs. not complete until fertilization (stays in mid meiosis I until ovulation then goes to metaphase II; ovum not created until fertilization)
what is the reduction division and when does it take place?
reduction in number of chromosomes from 2N–>N when centromeres divide
- occurs at anaphase I
- potential for nondisjunction
Down Syndrome
trisomy 21; most common form of mental retardation, level of severity based on when nondisjunction event occurs
Patau Syndrome
trisomy 13; punched in head, polydactyly
Edwards Syndrome
trisomy 18; specific hand sign
Lyon hypothesis
- x inactivation in all female somatic cells (or anytime there are two x chromosomes)
- inactive x condensed into barr body (epigenetic modification)
- reactivated during female meiosis; gametes must be XX
Hereditary non-polyposis colon cancer
-defect of mismatch repair pathway; causes mutator phenotype and thus accumulates DNA mutations more rapidly than normal
Ataxia telangiectasia
mutation in ATM gene that codes for protein important in replication stress response (which halts replication if DNA is damaged or there is a nucleotide shortage)
Bloom syndrome
mutation in BLM gene that codes for protein important in replication stress response (which halts replication if DNA is damaged or there is a nucleotide shortage)
Xeroderma pigmentosum
consequence of unrepaired DNA damage; inability to repair ace damage resulting from UV exposure increases mutational burden in cells and eventually neoplastic transformation
what are the ways in which medications can permeate cell membranes?
- hydrophobicity (passive diffusion)
- hijack transporters (make it look like something normally transported)
- package in lyposome
- protein transduction (sequences interact directly with membrane)
Kleinfelter syndrome
XXY; males with broad phenotypic expression (tall, man boobs); usually infertile
Turner Syndrome
result of a rare nondisjunction error
- 45, X; females with short stature, neck webbing, usually infertile
- 45, X/46, XY mosaicism may have male or female phenotype (male=normal, female=turner with increased risk of gonadoblastoma)
Androgen Insensitivity
XY female: mutation of androgen receptor gene located on long arm of X, TDF initiates male development but pathway blocked; infertile due to nonfunctional genitalia
Congenital adrenal hyperplasia
XX “male”; autosomal recessive, mutation results in overproduction if androgens in female fetus (androgens can cross placenta)
Wolf-Hirschorn Syndrome
4p-; chromosome deletion, phenotype displays in Greek warrior helmet head, risk of seizure, and need for specialEd
What is Tm and what affects it?
temperature at which 1/2 of DNA has melted
- size matters (bigger, the higher the Tm)
- high G+C content = high Tm
- high salt = high Tm
- high [OH] = low Tm (inversely proportional to pH)
- formation of H-bonds with bases stabilize single-stranded DNA and decrease Tm
30nm chromatin fiber
DNA coiled around 8 positively charged histones (H2A, H2B, H3, H4 x2); attaches to H1
Explain the mechanism of import through NPC
protein with nuclear localization signal bound to importin (directs docking on NPC); complex translocated to the nucleus; RanGTP (GEF catalyzed GDP–>GTP) binds importin, cargo released. RanGTP-importin complex diffuse to cytoplasm, RanGAP hydrolyzes GTP–>GDP and importin is recycled
Explain the mechanism of export through NPC
RanGTP, exportin and cargo are translocated to the cytoplasm; hydrolysis of GTP–>GDP by RanGAP causes complex to dissociate, export cargo is released.
nucleolus
primary function is ribosome biogenesis;
- granular component: maturing ribosomal particles
- dense fibrillar: active ribosomal synthesis
- fibrillar center: no active synthesis
microfilaments
- globular actin
- dynamic, important for cell shape
- structural polarity; uses myosin (towards +end)
- treadmilling (monitored by thymosins and profiling): ATP bound actin assembles into filament, assembled subunits hydrolyze ATP, ADP-actin dissembles (at - end) and free subunits exchange nucleotide over time
list actin-associated membrane structures
- microvilli
- lamellipodia; branched filaments, assemble on ARP complexes until the ends until capped,
- contractile ring in dividing cell
- stress fibers
describe the regulation of skeletal muscle contraction
- attached: short-lived rigor, myosin lacks ATP and is tightly bound to actin
- released: normal relaxed state, ATP bound and myosin not attached to actin
- cocked: ATP hydrolysis causes translocation of head to cock it in preparation for power stroke, weak actin affinity
- force-generating: dissociation of Pi increases affinity of myosin for actin, activates power stroke
- attached: dissociation of ADP by translocation of myosin head back to original configuration
robertsonian translocation
centromere to centromere translocation involving acrocentric chromosomes; results in loss of both short arms; normal offspring but only 45 true chromosomes
paracentric translocation
break on same side of centromere; inversion loop to pair properly; arm ratio unchanged, no problem unless recombination within the loop (no viability, apparent suppression of recombination)
pericentric translocation
break on opposite side of centromere; inversion loop to pair properly; results in duplication and deletion of genes (changes arm ratio); larger the inversion, the more viable the gametes
intermediate filaments
no structural polarity, high tensile strength, assemble into rope like filaments
- keratins: epithelia, mutation causes skin blister disease
- vimentin: mesoderm; connective tissue, muscle cells, and glial cells
- neurofilament proteins: nerve cells
- nuclear lamins: inner surface of inner nuclear membrane; mutation causes progeria
microtubules
- a and ß tubulin heterodimer
- associate with dyneins and kinesins
- dynamic instability
- stabilized by MT-associated proteins in nerve
- gamma tubulin: triplet MTs that form centrosomes
describe dynamic instability
allows MT array to search cytoplasm for structure to which to attach
- GTP bound assemble, ß can hydrolyze GTP to GDP; if assembly faster than hydrolysis, MT grows
- maturation: no more dynamic instability
roles of dynein and kinesin as MT motors for MTs
dynein to -end; kinesin to +end
ex. neuron: outward = kinesin (e.g. neurotransmitters), inward = dynein (e.g., recycled membrane, neurotropic viruses)
ex. non neural cell: kinesin stretch ER from nucleus, dynein keeps golgi near nucleus
Kartageners Syndrome
lack of motility in what should normally be motile cilia, results in respiratory diseases, infertility in males, heterodoxy
Polycystic Kidney Disease
mutation in protein needed for assembly of nonmotile cilia, results in abnormal growth regulation of epithelial cells and formation of cysts
describe protein import into mitochondria
powered by ATP hydrolysis and electrochemical gradient across inner membrane; TOM receives mitochondrial sorting signal, lateral diffusion until TIM encounter, translocated through Tom and then TIM; hsp70 translocate protein in unfolded state, signal peptidase cleaves sorting signal, hsp60 folds protein
peroxisome
- oxidative degradation with catalase
- beta oxidation
- synthesis of cholesterol, bile acids, lipids
Zellweger Syndrome
problem importing enzymes into peroxisome, severe defects and early death
X-linked adrenoleukodystrophy (ALD)
lack membrane protein for long chain fatty acid degradation, leads to demyelination of neurons; lethal without stem cell transplant
-HIV derived lentiviral vector for gene therapy
describe the process of cotranslation transport from cytosol to the ER
- signal recognition particle slows translation process so there is time to interact with ER membrane
- binds with SRP receptor, synthesis through the membrane, signal peptidase cleaves signal sequence
- released into lumen for golgi sorting unless hydrophobic stop-transfer sequence is present
smooth ER functions
- synthesis of steroid hormones
- detoxification of lipid soluble drugs
- protein modifications (N-linked co-translationally)
- quality control by chaperones; unfolded protein response up regulates chaperones/hsps as needed
golgi functions
- protein sorting
- processing to create glycoproteins and proteoglycans (O-linked by glycosyltransferases)
glycoproteins
- mostly protein, little carb
- N-linked: blocks of sugars added as a whole (in ER)
- O-linked: build one sugar at a time (ex. mucins, ABO blood group antigens) by glycosyltransferases (in golgi)
proteoglycans
- mostly carb with a little protein
- highly negatively charged because of carboxyl and sulfate groups, forms lubricants and gels
LDL receptor
types of constitutive pinocytosis (receptor mediated endocytosis); mediates the endocytosis of LDL, associate with clathrin coated pits and internalized with bound LDL; vesicles fuse with early endosomes; LDL dissociates in lysosome where it is hydrolyzed to free cholesterol
macrophage
type of phagocytic cell that phagocytoses red blood cells
transcytosis
typically occurs in a polarized cell, ex. lactating women: antibodies in blood are taken up by epithelial cells and sorted into early endosome and set from apical surface into breastmilk
endocrine signaling
signals are carried through blood stream, highest affinity receptors
synaptic signaling
signals have very small location to traverse, lowest affinity receptors
primary signal transduction
mechanism by which nuclear receptors regulate gene expression; ligand (hormone) binds to receptor, DNA-binding portion within nucleus is exposed and receptor can bind to all genes with matching promoter sequence
types of transmembrane surface receptors
- ion-channel linked
- GPCRs
- Enzyme-linked
adenylyl cyclase pathway
Gs binds and activates adenylyl cyclase, catalyzes conversion of ATP into cAMP, cAMP diffusions through cytoplasm and activates PKA which can then phosphorylate other proteins; Gi inhibits cAMP production
Gq
activates PLC which generates IP3 and DAG; –DAG: second messenger that activates PKC
-IP3: binds gated channels in ER to release Ca 2+
Calmodulin
protein that changes conformation dramatically when Ca 2+ ions bind to its 4 Ca binding sites; Ca 2+ calmodulin activates MLCK which phosphorylates myosin light chain kinase; enables myosin cross bridge to bind actin filament and allow for muscle contraction
receptor tyrosine kinases
dimerize to phosphorylate itself (no conformational change); common receptors for growth factors (choices between cell division and differentiation)
ex. SH2 domain binds/activates Ras, Ras with GTP bound activates MAP kinase cascade, MAPkkk–> MAPkk–> MAPk–> increases cyclin gene transcription and inactivates inhibitor proteins (increase [CDK] activity = passage into cell cycle)
adhering/anchoring junctions
maintain tissue integrity
- adherens: cell-cell, cadherins, actin
- focal adhesions: cell-ECM, integrins, actin
- desmosome: cell-cell, cadherins, IF
- hemi-desmosome: cell-ECM of basal lamina, integrins, IF
tight junctions
permeability barrier across epithelial sheets; maintains polarity; claudin and occluding;
gap junctions
connexon pores provide communication between neighboring cells; ex. electrical conduction in cardiac muscle; regulated by solute concentration, pH, phosphorylization
fibrous proteins
- collagen: tensile strength, ehlers danlos syndrome; pro peptide cleavage allows for higher order structures
- elastin: elasticity, proline, resists stretching, mar fans syndrome
- keratins
allelic heterogeneity
different mutations at the same locus cause same disease (ex. different mutations in the β-globin gene = thalassemia)
locus heterogeneity
mutations at different locus cause same disease (ex. autosomal dominant, autosomal recessive, and X-linked origins but only 1 mutant locus = retinitis pigmentosa)
clinical heterogeneity
same gene mutations cause different disease phenotypes
haldane’s rule
applies to x-linked recessive with no maternal family history other than one affected boy with reduced fitness; exception: fragile x
2/3 carrier status of parent and 1/3 carrier status of sibling
chimera
blending of 2 different zygotes; in germ line then genetically, children are niece and nephews
4 stages of cell cycle
- G1: gap before DNA synthesis, most cells
- S: DNA replication, histone synthesis
- G2: gap after DNA synthesis; addition of cohesins to link sister chromatids and condensins to condense chromosomes
- M: centrosome duplication and mitosis
mitosis
- prophase: chromosomes condense, spindle forms, nuclear envelope break down signals prometaphase (chromosomes attach to spindle MTs)
- metaphase: alignment at metaphase plate; tension on kinetochores activates anaphase promoting complex
- anaphase: chromosomes move closer to poles and further from each other
- telophase: cytokenesis; spindle disassembly/ nuclear reassembly;
cyclin dependent kinase
CDKs regulate major cell checkpoints; gradual increase in [cyclin] reflects continuous protein synthesis; turned off by ubiquitylation by E3 ubiquitin ligase
-G1/S: start
G2/M: enter M
Metaphase/Anaphase: exit M
p53
stabilizes CDK protein against proteolytic degradation; binds DNA and activates expression of p21 gene; p21 protein binds molecules important for the G1/S transition in the cell cycle; mutant p53 means no available p21 to act as the “stop signal” for cell division
internal controls of G1/S progression
- apoptosis: programmed cell death, cyc c–> caspase cascade
- terminal differential: cell only expresses genes specific to cell type and function; nonreversible
- senescence: cells in culture stop devising after 50-100 divisions due to absence of telomerase
external controls of G1/S progression
- growth factors: concentration and cell-type specific; local (PDGF wound repair) and systemic (ex. erythropoetin)
- cell-ECM interactions (stimulate)
- cell-cell inhibit
oncogenes
disregulated (mutated or over expressed) version of genes normally found in cellular genome (protooncogenes); just need a single allele to give rise to abnormal growth, not usually inherited
tumor supressor genes
act antagonistically with protocongoenes to inhibit growth; both alleles must be mutated or deleted, often inherited (predisposition for cancer)
ex. p53
DNA viruses
ex. HPV; carries genes in their normal genome that encode proteins that block Rb and p53 function; leads to hyperproliferation/ transformation of infected cell
bulky filler proteins
resist compression, proteoglycans and GAGs in cartilage
cross-linking proteins
fibronectin and laminin
basal lamina
specialized ECM, links tissues with connective tissues
what is different in cancer cells?
- do no senesce (active telomerase or inactive p53)
- lack growth factor dependence
- lack anchorage dependence (grow in suspension)
- no cell-cell contact inhibition (cells pile up on each other)
proto-onocogenes
stimulate growth code for important proteins at all levels of cell growth pathway
myosin I
monomeric, stand alone vesicle motor; walk along actin filament towards + end
myosin II
dimerizes, associates with light chains; head contain ATPase motor domains; phosphorylation of light chains leads to smooth muscle contraction
classes of signaling molecules
- small, diffusable molecules
- hydrophobic (steroids and eicosinoids)
- hydrophilic (peptides, amino acid de
- sensory signals
what affects membrane fluidity
- temperature
- length and degree of unsaturation: longer chain has more van der waals attractions
- cholesterol content: planar and stiff (decreases fluidity by preventing rotation, can increase by preventing packing)
- lipid rafts are less fluid
Shrimpton Diseases & MOI
Hemophilia A; XLR CF; AR α-1-Antitrypsin def; AR DMD; XLR Tay Sachs; AR Sickle cell disease; AR α and β Thalassemia; AR
Dynamic Mutations
Fragile X X!?
HD AD
DM AD
flippase
catalyzes transfer of specific phospholipids to cytosolic monolayer; gives asymmetric distribution of phospholipids
scramblase
catalyzes transfer of random phospholipids from one monolayer to another
replication stress response
replication forks are vulnerable to DNA damage or nucleotide shortage; checkpoint mechanisms halt replication if this happens and up regulates repair proteins
DNA repair mechanisms
- template-independent damage (direct reversal)
- ssDNA damage (requires intact copy)
- dsDNA breaks: NHEJ is preferred in humans, homologous recomb is better though
ribosome biogenesis
45 rRNA is transcribed, acts as a precursor that is then processed by enzymes to make 28S, 18S, and 5.8S; 5S; 18S leaves to make 40S and 5S joins to make 60S; large and small subunits are assembled and then exported out of nucleus to come together as 40S and 60S
conjugation
horizontal gene transfer through plasmids
transformation
pick up DNA from environment
transduction
bacteriophages pick up flanked DNA which can then be delivered to new host
transposons
code for transposases that catalyzes transposition; retrotransposons move via RNA intermediate
retroviruses
ssRNA genome that gets converted to dsDNA by viral reverse transcriptase; viral promoters can be very active so insertion can inappropriately turn on neighboring genes
why are flanking intragenic markers more useful than markers on the same side?
it would take a double crossover rather than a single crossover to cause an error with flanked markers
adaptin
mediate the formation of vesicles by clathrin-coated pits through interaction with membrane-bound receptors
what are the genetic/biochem differences between type A, B, and ABO?
differ in the transferase enzymes encoded at ABO locus, adds terminal sugars on the glycoproteins and glycolipids on the surface of the blood cell
- type A: GalNAc
- type B: Gal
- type AB: both
- type O: no terminal sugar
