Weeks 6-7 - Muscles + Embryology Flashcards
(127 cards)
1
Q
Skeletal muscle: What is a myofibril? What is a muscle fibre (posh name too)?
A
A bundle of sarcomeres
Hundreds of myofibrils - a syncytium
2
Q
Skeletal muscle: What is the length-tension relationship?
A
Few myosin heads have access to actin at full stretch, force is weak (vice versa)
3
Q
Skeletal muscle: What is endomysium? What is perimysium? What is epimysium?
A
Loose connective tissue surrounding each muscle fibre, connecting to basement membrane
Mixed connective tissue separating fascicles
Loose connective tissue between fascia and muscle body
4
Q
Skeletal muscle: What is a fascicle? What is fascia?
A
Bundle of muscle fibres, held by perimysium
Dense connective tissue layer covering muscle
5
Q
What is skeletal muscle adapted for?
A
+ power generation
Controlled movements
6
Q
What are the properties of cardiac muscle?
A
- Has mono or denucleated single cells (cardiomyocytes) with limb-like extensions, connecting neighbouring cells
- Cross striations
- Centrally located nuclei
- Extensions connected via intercalated discs
- Lots of mitochondria
- Each cardiomyocyte has a basement membrane
- Adapted for rhythmic wall contractions
7
Q
Cardiac muscle: What are intercalated discs?
A
Desmosomes and low resistance gap junctions (allowing membrane depolarisation transfer)
8
Q
What are the properties of smooth muscle?
A
- No myofibrils or striations
- Adapted for high amplitude contraction, high versatility and low power output
- Extension requires antagonistic force
9
Q
What is a motor unit?
A
Motor neuron + muscle fibre it is attached to
10
Q
Cardiac muscle: What is short axis? What is long axis?
A
Mid ventricular section
Oblique sagittal plane
11
Q
What increases cardiac pump? What is the route of cardiac action potential?
A
Inotropy - increased contraction force
Chronotropy - increased contraction frequency
Propagated along sarcolemma, into T-tubules
12
Q
What causes plateau in cardiac muscle graph? What is the role of calcium transient? What is essential for cardiac contraction?
A
Ca2+ influx from extra-cellular space
Key to drug action as many work on Ca2+ transient modulation (i.e. caffeine)
Extracellular Ca2+
13
Q
What does increasing cardiomyocyte length do? Why does digitalis work?
A
Increases Ca2+ sensitivity
Increases heart function as it increases Ca2+ release, so increased contractility
14
Q
Where are 3 locations of ATP origin in cardiac muscle?
A
70% = from fat oxidation
20% = from glucose oxidation
10% = from other sources
15
Q
What are the functions of smooth muscle? What are some of its properties?
A
Digestion, breathing, reproduction
- Normally partially contracted
- Forms net-like structure meaning shape can be altered
16
Q
What are the structural organisations of smooth muscle?
A
Single sheets = circular orientation, varied diameter (flow and pressure control)
Multiple sheets = two perpendicular sheets, varied diameter and length (peristalsis)
17
Q
Why are muscles called striated muscle?
A
Intermediate filaments form centre of sarcomere, held in register by cross connections at every Z disc and middle of sarcomere
18
Q
Why do ventricles form wringing motion when the contract?
A
Due to spiral, fibre like arrangement of cardiomyocytes
19
Q
Why can smooth muscle contract further than striated muscles? What is the role of intermediate filaments? What holds together actin filaments?
A
Upon contraction, it shortens but diameter increases
Prevent over-stretching by forming a scaffold
Patches of cytoskeletal proteins (dense bodies)
20
Q
How is contraction controlled in skeletal muscle?
A
- Motor nerves of somatic nervous system
- Alpha motor neurons innervate force producing fibres
- No gap junctions so APs only generated by motor end plates (1 synapse per fibre)
- Quick feedback
- Allows precise movement control
21
Q
What is the route of cardiac depolarisation?
A
- SAN
- Atria
- AV node
- Purkinje fibres
22
Q
What are the properties of Purkinje fibres?
A
- Have aligned purkinje cells (large heart cells filled with glycogen granules in centre)
- Generate robust APs which travel to ventricles
- Individual activation of cardiomyocytes
23
Q
What is mentioned in Stirling’s Law of the Heart?
A
Increasing diastolic length of cardiomyocyte increases its’ sensitivity to Ca2+
24
Q
What are the properties of muscular tissue?
A
Derived from mesoderm and composed of cells with filaments of contractile proteins in cytoplasm
25
What are the properties of multiunit muscle? What are the properties of single unit muscle?
Nerves interact with all muscle cells as structurally independent
- Each unit requires separate stimulation
- Neurogenic Nerves interact with some muscle cells, electrically coupled by gap junctions
- AP propagates between cells
- Myogenic
- Stretch-relaxation response (i.e. bladder, where connective tissue prevents over-stretching and allows hollow organs to fill with maintained muscle tension)
26
What are varicosities? What are the properties of calcium in regards to smooth muscle (contraction)? How does noradrenaline affect Ca2+ (relaxation)?
Where nerves meet muscle and neurotransmitter release - + extracellular calcium conc.
- Influx via voltage-gated channels
- Intracellular calcium stored in sarcoplasmic reticulum
- Ca2+ binds to calmodulin, activating enzyme MLCK, phosphorylation
Reduces Ca2+ conc, dissociation of calmodulin from MLCK, no phosphorylation
27
What are the differences in calcium in smooth muscle?
- Source differs from skeletal muscle
- Influx across plasma membrane
- Mobilised from intracellular stores
28
What are the 3 methods of muscle catabolism?
- Ubiquitin-proteasome protein degrading system
- Autophagy
- Calcium-activated proteases
29
How is muscle breakdown prevented and what is muscle atrophy?
Repair damaged fibres (after exercise)
When muscle breakdown exceeds synthesis
- Late cancer or HIV stages
- Cytokines are released, increasing degradation
- Enzymes involved in ubiquitin-proteasome pathway increased
30
What is nitrogen balance? Where does it occur? What is positive and negative nitrogen balance?
- Amino acids cannot be stored and NH4+ is removed to form ammonia
- NH4+ is converted into urea and excreted via urea cycle
- Remaining carbon skeleton from AA NH4+ removal is used for energy
Liver
Positive = nitrogen intake \> loss (pregnancy, growing child, injury)
Negative = nitrogen intake \< loss (starvation, illness, fever, ageing, cancer cachexia)
31
What diseases are associated with nitrogen balance? Where do we get essential AA's from?
Kwashiorkor Aminoacidopathies
Maple syrup urine disease (defects of branched chain amino acid metabolism)
Black urine disease
PKU (defects of phenylalanine metabolism)
Our diet
32
How is NH4+ formed? What are the details of the processes?
Via transamination and oxidative deamination
Transamination = amino acid to glutamate = alpha amino acid + alpha-ketoglutarate --\> alpha keto acid + glutamate
- Requires alanine aminotransferase enzyme
Oxidative deamination = glutamate to NH4+
33
What are the properties of the urea cycle?
- 1 nitrogen = from transamination / deamination and other from aspartate
- Glucogenic amino acids carbon skeletons increase glucose concentration
- Ketogenic amino acids carbon skeletons increase ketone body concentration
34
What is neuromuscular? What are synapse properties? What is a myocyte?
Affects both neural and muscular tissue
- Unidirectional
- Irreversible delay
- Chemical A muscle fibre cell
35
What condition is associated with neuromuscular junction and what are its properties? What is the treatment?
Myasthenia gravis:
- Affects 1 / 10 - 20,000, 2X more women than men
- Autoimmune disorder
- Autoantibodies are produced against nicotinic ACh receptors
Treatment = increase acetylcholine levels at NMJ by preventing ACh metabolism
36
What are neuromuscular junctions?
- Synapses between every muscle and neurones
- Single axon to single muscle fibre (eye muscle)
- Single axon to many muscle fibres (bicep)
37
What is the route of action potential to muscle fibre contraction?
- Action potential at axon terminal
- Terminal membrane depolarisation
- Voltage-gated calcium channels open
- ACh exocytosis into extracellular space mediated by calcium
- ACh and nicotinic receptor interaction
- Conformational change
- Na+ influx, K+ efflux from muscle cell
- AP generated if receptor generator potentials pass threshold
- AP propagation through muscle
- Ca2+ release from sarcoplasmic reticulum
- Muscle contraction
38
How do you measure action potential? How do you measure muscle contraction/ How do you terminate ACh action? How do you deactivate ACh release?
Electrophysical recordings
- Electrophysical recordings
- In vivo or ex vivo
- Record before, during or after motor neuron stimulation
Enzyme acetylcholine esterase
Enzymic hydrolysis in synaptic cleft
39
What is quantal exocytosis?
- Small ACh quanta release at rest
- Bind to nicotinic receptors
- Small membrane depolarisation
- 0.4mV miniature epp
- Increased ACh release detection capacity
40
What is personality? What are the two types?
Individual differences in thinking, feeling and behaviour patterns Type A = hostile, aggressive, impatient
Type B = relaxed, live in the moment
41
What are the big 5 (OCEAN)?
Openness to experience
Conscientiousness
Extraversion
Agreeableness
Neuroticism
42
What are the links between OCEAN and smoking? What are the links between OCEAN and healthy living?
+ N and + O = + cigarette use
+ N = higher lifetime smoker risk
+ O = low lifetime smoker risk
+ C = better lifestyle
43
What are the main aspects of high N, E, C and A?
+ N = + health worries
+ E = + risk taking
+ C = + worry about effect of behaviour on others
+ A = + optimistic, + trust in people
44
Shontz's model stages of reaction to diagnosis?
- Shock
- Encounter reaction (emotions, anger)
- Retreat (denial)
- Reality
45
What is the crisis theory? What are the order of events?
Describes factors which influence process of adjustment / adaptation to a diagnosis
- Background factors
- Cognitive appraisal
- Adaptive tasks / coping
46
What external factors influence illness appraisal?
- Stability
- Prognosis
- Visibility
- Physical impairment
- Pain
47
What patients factors influence illness appraisal?
- Age
- Social class
- Gender
- Psychological resources
- Self-blame
48
What are the ways to self-manage a chronic illness?
- Lifestyle change
- Medication use
- Adjusting to symptoms
- Maintaining good relationship with practitioner
49
What are the 2 emotional response categories? What is problem focused coping? What is emotion focused coping?
- Avoidance and inhibition of emotions
- Acceptance and expression of emotions
Reduce demands / increase resources
Minimise emotional response (drinking, drugs)
50
What are the properties of RNA?
- Single stranded
- Helical, right-handed structure
- Van der Waal and base stacking
- Strong purines
- + reactive than DNA
- rRNA, tRNA, mRNA
- DNA-dependent RNA polymerases for production
51
What are the properties of RNA synthesis?
- Initiated at DNA specific sites
- Expression = single strand, small genome portions
- Template strand (coding strand) is fully conserved and no primer is required
- Coding strand = same sequence as RNA
- Protein-coding genes = structural genes (individually transcribed in eukaryotes, together in prokaryotes)
52
What is the function of RNA polymerase? What are the function of promoters? What is the function of a transcription bubble?
Couples ribonucleotide triphosphates
Allow RNAP to bind to initiation site on 5' side of TSS
Allows RNA synthesis, no RNAP dissociation from template, initiation stimulated as much as sterically possible
53
What are the properties of RNAPs? What are general transcription factors required for?
- + mass = + subunit complexity
- Enhancers = sequences that encourage transcription
RNAP ll transcription
54
What are some transcription inhibitors and their properties?
Rifamycin B
- rifampicin is synthetic derivative and inhibits prokaryotic transcription
Elongation prevention
- no further initiation as inactivated RNA still bound Actinomycin D
- polymerase passage interference and inhibits DNA replication and transcription
Death cap mushroom
- elongation blocked, binds beneath polymerase bridge helix, alpha-amanitin binds to RNAP ll
55
What are the different types of RNA processing and their properties?
RNA capping
- provides degradation resistance and enzymatic reactions required
Polyadenylation
- influences mRNA stability and prevents degradation
Splicing
- spliceosomes carry it out, forming spliceosome complexes.
Intron sequences are paradoxical
Alternative splicing = proteins have different cell destinations and catalytic properties
56
What forms the preinitiation complex?
DNA + enzyme + general transcription factor
57
What is a congenital abnormality?
Altered structure or function of tissue / organ that presents at birth or is result of process before birth
58
What are examples of major congenital abnormalities?
- Holoprosencephaly
- Cleft lip or palate
- Ventricular septal defect
- Diaphragmatic hernia
- Intestinal malrotation
- Imperforate anus
59
What are examples of minor congenital abnormalities?
- Brushfield spots
- Epicanthic folds
- Preauricular pit
- Single palmar crease
- 5th finger clinodactyly
- 2/3 toe syndactyly
60
What is malformation? What is disruption? What is deformation? What is dysplasia?
Primary morphogenesis error
Destruction of normally developed / developing tissue / organ
Mechanical distortion of normally developed / developing tissue / organ
Abnormal cell-to-tissue organisation
61
What are examples of multifactorial abnormalities?
- Cleft lip ± palate
- Congenital heart disease
- Congenital hip dislocation
- Congenital hypertrophic pyloric stenosis
- Neural tube defects
- Hypospadias
- Talipes
62
What are examples of teratogenic drugs?
- ACE Inhibitors
- Alcohol
- Anticonvulsants
- Carbamazepine, Sodium valproate
- Thalidomide
- Vitamin A
- Warfarin
63
What are examples of infectious teratogens?
- Cytomegalovirus
- Herpes simplex
- Parvovirus B19
- Rubella
- Varicella zoster
- Syphilis
- Toxoplasmosis
64
What are the complications of congential rubella?
- High risk of fetal infection in first trimester
- Cataracts, ocular abnormalities, congenital heart disease
- Sequelae (deafness, blindness, microcephaly, mental retardation)
65
What are examples of maternal illnesses?
- Diabetes mellitus
- Phenylketonuria
- Hyperthermia
- Systemic lupus erthymatosus
- Myasthenia gravis
66
What are the properties of most eukaryotic genes? What can affect transcription control?
- Require transcriptional regulation of gene expression
- Controlled by cis-acting sequences
- Binding of sequence-specific TFs to DNA
- Control of DNA packaging and chromatin structure
67
What are the properties of transcription factors?
- Function as dimers (homo or hetero)
- General or transcription regulators
- Interact with DNA major groove bases
- Eukaryotic function in groups
- DNA binding ones recruit other regulators (co-activators and repressors)
68
What are the properties of chromatin in gene regulation?
- Eukaryotic DNA condensed
- Modification of structure central to transcriptional regulation
- Requires DNA and histone interaction for formation
69
What do pax 3 and pax 6 mutations cause?
Pax 3 = type 1 Waardenberg syndrome
Pax 6 = developmental abnormalities
70
What are the properties of mRNA stability?
- Competition between translation and decay
- Cytosolic mRNA de-adenylated leading to mRNA degradation
- Iron controls own uptake into cells
- Regulated by iron
71
What is a clinical trial? What are the 4 phases?
Research study where treatment or management plan under test is administered to humans
1 = small human group for safety and dosage and administration route
2 = efficacy study with or without control group
3 = large scale study with controls
4 = post marketing studies on rare adverse effects without control
72
What is a parallel group-controlled trial? What are the benefits?
Investigator allocates the exposure group
- Avoids chance, bias, reverse causality or confounding being responsible for results
73
What are the 2 chance errors in clinical trials?
Type 1 - incorrect H0 rejection (believing treatment worked if it didn't)
Type 2 - incorrect H0 acceptance (reduce risk with + study size and power calculation using 1 - Beta (probability))
74
What are common excluded groups in clinical trials? Why may a trial be inappropriate?
- Pregnant women
- Children
- Patients with multiple illnesses If harm may be done and is unethical
75
What are difficulties of clinical trials?
Rare conditions don't have enough cases
Delay between treatment and outcome (expensive follow-up)
76
When is a cross-over trial used? When is an equivalence study used? Why are power calculations used?
When cure is not the outcome
Establishment of new treatment is equivalent, not better
Ensure important group differences are detectable
77
Why is sub-group analysis used?
- May have different response to treatment
- Separate analysis
- Validly addresses hypothesis if pre-specified sub-groups before trial
- Hypothesis generated if done after start of trial
78
Examples of X-linked recessive disorders?
- Duchenne Muscular Dystrophy
- Becker Muscular Dystrophy
- Haemophilia
- Red-Green Colour Blindness
- G6PD deficiency
- One form of Hereditary Motor & Sensory Neuropathy (Charcot-Marie-Tooth Disease)
- Retinitis Pigmentosa
79
What are the properties of Deuchenne muscular dystrophy?
- Most common & severe form of muscular dystrophy
- Presentation = 3-5yrs -~ 33% have mild-moderate learning difficulties
- Waddling gait & positive Gower sign
- Difficulty running and climbing stairs
- Gradual deterioration -\> Loss of mobility =\>Wheelchair bound
- Progressive muscle weakness -\> Cardiorespiratory failure
80
Examples of autosomal recessive disorders?
- Hereditary Haemochromatosis
- Cystic Fibrosis
- ß-Thalassaemia
- Spinal Muscular Atrophy
- Many Inborn Errors of Metabolism
- Some Sensorineural Deafness
- 21-Hydroxylase deficiency
81
What is the risk of being a carrier is sibling is affected by a recessive disorder? What is the Hardy-Weinburg equation?
2/3
Calculation of carrier rates when condition incidence is known and gene frequency is in equilibrium --\> p + q = 1
82
What are germline mutations? What are somatic mutations?
Inherited mutations present in every cell
Acquired mutations present in diseased tissue
83
What are germline clinical utility of molecular testing?
- Confirm diagnosis
- Screen at risk mutation carriers
- Prenatal diagnosis
- Pharmacogenetic testing
- Screen populations
84
What are somatic clinical utility of molecular testing?
- Tumours
- Diagnosis / tumour classification
- Prognosis
- Prediction of tumour chemotherapy response
- Pharmacotherapeutic testing
85
What are challenges of molecular testing?
Lots of mutation types --\> single base to large chromosomal fragments
Requires different tests for different mutations
Multiple tests for different types of mutation in same gene with same effects
Some genes have mutation hotspots
Same phenotype with multiple mutations in same gene sometimes
Different mutations with same gene may give different phenotypes
Same syndrome from mutations in different genes (locus heterogeneity)
86
Examples of some mutation hotspots?
- Almost all Huntington mutations in same gene region
- 80% CF mutations are ‘delta’F508
- 90% Kras mutations in codon 12/13
- Allow tests to be targeted
87
What are the properties of muscular dystrophy?
- Both due to deletion in Dystrophin gene
- Duchenne’s due to frameshift mutation
- Becher’s due to in-frame deletions, so partial function loss
- Both = 60% mutations are deletions of whole exons in 2 hotspots -X-linked muscle wasting disease
- Symptoms appear aged 2-5
- Death secondary to cardiac dysfunction / respiratory complications in DMD
- Becker’s = survive to old age
88
Where do you derive DNA from for molecular testing?
- Blood lymphocytes
- Mouthwash cells
- Chorionic villi
89
What are the properties of sequencing for molecular testing?
- Most common = Sanger sequencing
- Pyrosequencing = newer and more sensitive
- Not easy and expensive
- Scanning before sequencing is ideal
90
What are the properties of methylation specific PCR for molecular testing?
Detects epigenetically silenced alleles DNA modified by bisulphite reaction --\> non-methylated cytosine to thymine Methylation specific primers used for presence / absence detection of PCR product
91
What are the requirements for BRCA 1/2 genetic testing?
- Genetic counselling
- Germline testing
- Screening of whole gene due to heterogeneity
- 63 PCRs required
- Mutations = small insertions or deletions
- Heteroduplex analysis screening can be used
- PCR and direct Sanger sequencing required for test
92
What are the properties of ribosomes?
Binds mRNA so codons are read
tRNA binding sites Binds to non-ribosomal factors (allows polypeptide chain initiation, elongation and termination)
Catalyse formation of peptide bonds Capable of movement (for sequential codon translation)
Prokaryotic (70S) = 2 subunits (large = 50S --\> 5S + 23SrRNA + 31 proteins, small = 30S --\> 16S rRNA + 21 proteins)
Eukaryotic = 40% bigger than bacterial à 80S, small = 40S (33 polypeptides + 18S rRNA), large = 60S (49 polypeptides + 28sS, 5.8S and 5S rRNA)
93
What are the types, and properties, of the tRNA binding sites?
- A site (aminoacyl site) = accommodates incoming aminoacyl tRNA
- P site (peptidyl site) = accommodates tRNA attached to growing peptide chain
- E site (exit site) = accommodates tRNA, without amino acid, that’s leaving
- All have anticodons bound to 30S subunit and rest is bound to 50S subunit
- A and P site tRNA have close mRNA interactions via base pairing
94
What are the properties of translation?
- Protein = made N – C terminal -5’ to 3’ reading of mRNA
- Chain elongation = linking growing polypeptide to incoming tRNA amino acid residue
- New peptidyl tRNA transferred from A to P site
- Uncharged tRNA moves to E site -Polycistronic = prokaryotic mRNA has +1 coding region (have own initiation and termination codons)
- Monocistronic = eukaryotic
- Polysome complex = +1 ribosome translates a message as mRNA is long
95
What is translation initiation?
- Before peptide formation
- 2 ribosomal units
- mRNA to be translated
- Aminoacyl-tRNA specified by 1st codon
- GTP -Initiation factors
- Ribosomes recognise start codon (Shine-Dalgarno sequence --\> binds with 16S rRNA of 30S subunit (not in eukaryotes – 40S binds to cap structure)
96
What is translation elongation?
- Addition of AA’s to carboxyl end of chain
- Next tRNA delivery by elongation factors --\> requires GTP hydrolysis
- Translocation --\> 3 nucleotides advanced to MRNA 3’ end
- Then elongation then translocation etc. until termination
97
What is translation termination?
Codons recognised by release factors (RF – 1 and RF – 2)
98
Examples of translation inhibitors?
Antibiotics block translation
Streptomycin (is an aminoglycoside) --\> - conc. = ribosomes misreads mRNA, + conc. = prevents chain initiation, so cell death
Chloramphenicol --\> inhibits peptide bond formation, binds near A site, can affect mitochondrial translation
Tetracycline --\> binds to small prokaryotic subunit, prevents tRNA entry to A site, stops synthesis
99
What happens during co/posttranslational modification?
- Chaperones help protein folding
- Many polypeptides modified before use (cotranslational = still attached to ribosome, posttranslational = after synthesis)
- Act/deactivation by covalent chemical group attachments
- Phosphorylation on hydroxyl groups, catalysed by kinases and reversed by phosphates
- Carb chain attachment = secreted or cell membrane proteins --\> N-linked = asparagine amide nitrogen attachment, O-linked = serine, threonine and hydroxylysine hydroxyl attachment --\> can occur in Golgi
100
What is signal recognition peptide?
Proteins ubiquinated after usefulness (76-residue protein ubiquitin added, protein sent for degradation)
SUMO (small ubiquitin-related modifier) addition signal cellular localization
Translocation of transmembrane / secretory proteins via secretory pathway through ER --\> associate with signal recognition particle, docks with ER receptor, post-translational modification occurs)
101
What are the properties of the cell cycle? What are the 3 parts of a chromosome?
- Lasts usually 24 hours
- G0 = cells not spontaneously dividing so mitogen use stimulates them
- 24 hour lag from mitogen use and entry to cell cycle Centromere, p arm (shorter), q arm (longer)
102
What is fluorescence in-situ hybridisation?
Labelling of single DNA strand with fluorescent tag
Is hybridised to target DNA attached to a slide
Hybridises with matching DNA sequence
103
What is the concept of dosage equilibrium? What is X-inactivation?
- X chromosome = 2 copies in women
- Double dosage if both X copied
- X inactivation occurs by switching off one copy in females
- Happens 2 weeks post fertilisation, at 5000 cell stage
- Random occurrence, all cells have same though
104
What are the signs of Down syndrome?
- Flat facial profile
- Upward slanted eyes
- Small ears
- Flat back head
- Tongue protruding
- Shortness
- Mental retardation
- Autism
- Cardiac defects
- + leukaemia risk
105
What are signs of Edward's syndrome?
- Growth retardation
- Small mouth
- Clenched hands
- Overlapping fingers
- Prominent heels and head
106
What are the signs of Patau syndrome?
- Scalp defects
- Narrow eye distance
- Polydactyly
- Cleft lip / palate
107
What are the signs of Turner syndrome?
- Short stature
- Webbed neck
- Low posterior hairline
- Small nails
- Hand and feet lymphoedema (extra skin)
- No secondary sexual development
- Infertile
- No learning difficulties
108
What are the signs of Wolf Hirschhorn syndrome?
- Deletion syndrome
- Prominent forehead and wide set eyes
- Broad beaked nose
- Mental retardation
109
What are the signs of Prader-Willi syndrome?
- Deletion
- Very floppy (hypotonia) when infant
- Marked obesity
- Learning difficulties
110
What are the symptoms of Angelman syndrome?
- Deletion
- Inappropriate laughter
- Convulsions
- Poor coordination
- Learning difficulties
111
What environmental agents cause mutations?
- UV (200-300nm) - promotes thymine dimer formation, distorting DNA helix and transcription / replication interruption
- Ionizing radiation
- Chemical agents
112
What do chemical mutagens do?
Point mutations (transversions / transition of bases) - caused by nitrous acid (deaminates aromatic primary amines) - prevents clostridium botulinum growth -
Mustargen = leads to loss of base, gap filled by error-prone enzymatic repair (transversion)
Insertion / deletion mutants ((+)1 nucleotide inserted / deleted)
113
What are properties of insertion/deletion mutation? What is a polar mutation?
- Arise from intercalating agent use
- DNA helix distorted as base distance is doubled
- Benzopyrene --\> found in cigarettes (polycyclic aromatic hydrocarbon) --\> wedges into DNA causes point mutation as G read as T
- Lead to frameshift mutations
Mutation affecting downstream genes / operons
114
What happens with large scale mutations? What is a point mutation?
Gross chromosomal changes
Genetic disease:
- Charcot-Marie syndrome, physical weakness, walking difficulties - Down syndrome – Trisomy 21 from whole chromosomal duplication
Can irreversibly alter cellular metabolism - cancer
115
What is the Ames test?
Use bacteria which can’t make histidine
Mutagenesis indicated by reversion to his+
Discover carcinogens
116
What happens during DNA repair?
- Enzymes reverse damage
- Direct reversal - photoreactivation restores pyrimidine dimers (catalysed by DNA photolyases), found in prokaryotes, splits dimer using light excitation energy
- Alkyltransfereases - reverse base methylation caused by alkylating agents
- Base excision repair - removal and replacement of bases - glycosylases cut out base - leave deoxyribose residue with no base
- AP endonuclease cleaves deoxyribose residue on 5’ side
- D and adjacent nucleotides removed by d phosphate lyase - gaps filled by DNA polymerase and ligase
- AP sites in mammalian DNA = + cytotoxic
- Ribose at AP site lacks glycosidic bond
- Nucleotide excision repair
- pyrimidine dimer repair - ATP dependent in E.Coli
- Xeroderma Pigmentosum – cells cannot repair UV-induced damage, dryness and skin tumours, eye damage, fatal cancers
117
What is mismatch repair?
Cut out bases by recognising methylation - defect = high cancer incidence
118
What is involved in double strand breaking?
- Generated by ionising radiation, free radicals, gene rearrangements, 5-10% dividing cells have it
- Repairing = Nonhomologous end-joining (NHEJ) OR recombination repair -NHEJ = re-joins DSBs, broken DNA ends must be aligned, trimming of frayed ends (can generate mutations), eukaryotes = Ku protein is broken DNA sensor
- Ku-DNA dimerises (aligns DNA)
- Homologous end joining = Occurs via 2 Hollidays Junctions, DSBs resected, 3’ ends invade other strand, DNA polymerase fills gaps, ligase seals joints
119
What happens during female gametogenesis?
120
What are the properties of spermatogenesis?
- By MITOSIS followed by MEIOSIS in the testes Results in HAPLOID spermatozoa
- Continuous from puberty ie stem cells retained
- Takes about 9 weeks
- About 300 x 106 per ejaculate
- Motile
- Low cytoplasmic:nuclear ratio
Fluid from other glands added prior to ejaculation
121
What are the properties of oogenesis?
- By MEIOSIS in the ovaries
- Results in HAPLOID ova
- Discontinuous: all primary oocytes (~ 2 x 106) are present at birth - no stem cells retained. Primary oocytes suspended part way through meiosis
5-12 primary oocytes continue with meiosis with each monthly cycle following puberty - but they do not complete meiosis until the moment of fertilization
Non-motile
V high Cytoplasmic:nuclear ratio
122
What happens during fertilisation?
123
What happens during cleavage?
- 2 daughter blastomeres form via mitosis
- Further cleavage = smaller blastomeres form
- Morula = solid cell ball, normal cytoplasmic:nuclear ratio, still zona pellucida
- Morula = cells undergo compaction and zona pellucida splits, tight junctions form between surface cells
124
What happens during blastocyst formation?
125
What happens during implantation?
126
What are the risks with 1 and 2 sac monochorionic twins?
1 sac = risk of twin-to-twin transfusion syndrome
2 sac = risk of cerebral palsy or miscarriage
127
