::) Flashcards
what is the difference in structure and function in
- superficial fascia
- deep fascia
superficial fascia:
- loose CT
- connects the skin to the underlying bones or deep fascia
deep fascia:
- *- dense fibrous connective tissue**
- encircle compartments within the body, particulary limbs and muscle compartments grouping muscles together
- means muscles share **same neurovascular supply
- avascular
- innervated**
describe structure of a DNA nucleotide [3]
how do nucleotides connect to make DNA stucutre? [2]
each nucleotide contains:
- deoxyribose (a pentose (five sugar carbon))
- *- nitrogenous bases**
- a phosphate group
how do nucleotides connect to make DNA stucutre? [2]
the nitrogenous bases in the helixes can interact with each other via H bonds: double structure [1]
these double strands of DNA twist around each other in anti-parralel direction: one runs (3’ -> 5’), the other runs (5’ -> 3’)
describe the differences between non-homologous end joining and homologous recombination for double stranded DNA repair
non-homologous end joining:‘quick and dirty.’ get scars on DNA (regions of altered segment due to missing nucleotides). occur in non-coding regions of DNA
homologous recombination: more accurate. sister chromsome is used as a template. complete sequence is restored by copying sister chromosome.
- why are double strand repairs of DNA more dangerous for single strand repair? [1]
there are no intact template strands to copy
- when does base excision repair occur?
- explain how base excision repair mechanism works
- correction of single bases that do not sig. distort DNA helix structure
- -single base is excised out (using an enzyme, such as uracil DNA glycosylase)
- DNA polymerase adds correct base and DNA ligase seals the deal
what is role of topoisomerase? (enzyme found in bacterial DNA replication pathway)
topoisomerase = prevents supercoiling of DNA. removes knots and tangles in bacterial chromosome.
describe how replication starts at the origins of replication for both:
- leading strand
- lagging strand
leading strand: synthesis occurs in 5’ to 3’ direction
lagging strand: synthesis cannot occur in direction continously (as would be in 3’ to 5’ direction). INSTEAD: synthesised in short segments (Okazaki fragments) of DNA in 5’ to 3’ direction. DNA ligase joins the okazaki fragments to form the second strand of DNA
which enzyme adds bases onto DNA to allow it synthesise?
DNA polymerase ! :)
describe and explain the structure of a chromosome
telomeres:
- at each end
- protective DNA cap.
- contains repetitive DNA
Centromere:
- found in centre
- keeps sister chromatids together and attaches them to microtubules
- repetitive DNA
- organised into short arm - p (petite) and long arm - q
what are the ways you can have abornmal chromsome structure?
chromomes can under go:
deletion
duplication
inversion
translocation (one part of a chr joins another part of a chr)
Robertsonian translocation (two long arms of acrocentric chr (13, 14, 15 21, 22) join at their centromeres
explain the three different patterns that can cause Down Syndrome
1. trisomy 21: 95% DS - three copies of chr 21
2. Robertsonian translocation (chrs 14 and 21): 4%. have an extra copy of chr. 21 due to aforementioned translocation
3. Mosiacism: 1%. have normal and trisomy 21 cell linearges. occurs postzygotically. milder features (some cells have normal genome, some cells have trisomy 21 genome)
describe 3 prenatal diagnoses that can be undertaken to test for aneuploidy
1. amniocentesis: genetic testing of amniotic fluid. using needle to extract transabdominal. 15-18 weeks of preg (risk to miscarriage: 1/100). ultrasound guidance used. t
2. chorionic villus sampling: genetic testing of tissue from placenta (choroinic villi), ultrasound guidance used transabdominal or transcervical. 12-14 weeks
3. non invasise technqiues: ultrasound imaging of back of neck of embryo at 11-14 weeks. if depth of fluid at back of neck is 3.5-4.4 mm = 70% chance of delivering baby with no major abnormalities.
what are point mutations?
what are the differnent mutations that are consequences of point mutations(4)?
point mutations: change in single base pair mutations. occur in DNA replication errors. most common mutation. substitution, insertion, deletion or inversion of base pairs.
consequences:
a) silent mutation - no change to a.a. sequence
b) missense mutation: changes one a.a. to another (conservative: swaps for a.a. with similar properties, non-conservative: swaps for a.a. with dissimilar properties)
c) Nonsense mutation: creates an early stop codon (creates shorter a.a. highly damaging)
d) frameshift: due to deletion or insertion shifts entire coding sequence by one or more bases due to deletion or insertion of bases
how can you classify types of mutations? explain each type (3)
at scale of mutation:
1. genomic change: whole chromosome gain / loss
2. chromosomal change: result from rearrangement of genetic material and give rise to visible structural changes in chr.
3. gene mutation: vast majority are single base pair changes / small number of base pair changes
what are the different types of chromosomal mutations?
name two diseaese / disorders from chromosomal mutations?
what are the different types of chromosomal mutations?
deletion, duplication (part of a chr breaks off and attaches to sister chromatid), inversions (part of a chr breaks off and reinserts backwards), insertions (part of one getes inserted to another chr), translocation (part of chr breaks off and attaches to different chr)
name two diseaese / disorders from chromosomal mutations?
1. Y - chromosome infert: deletetion part of Y-chromsome. called azoospermia factor (AZF) A, B or C
2. Charcot-Marie-Tooth disease (CMT1A): duplication of regions of chr 17. progressive loss of neurons
what are non-disjunction diseases?
Nondisjunction means that a pair of homologous chromosomes has failed to separate or segregate at anaphase so that both chromosomes of the pair pass to the same daughter cell.
lead to:
gain or loss of whole chromosomes. e.g. Down Syndrome: trisomy
how does UV radiation cause direct mutations?
how does UV radiation cause indirect mutations?
- *direct damage**
- cause DNA phoshpate backbone to break
- break BP connections
- alter bases
- cause intra-/inter- stand cross links
indirect damage:
ionizing radiation creates free radicals that damage DNA by reacting with i
what is the effect of DNA damage by UV radiation to melanocytes?
what does smoking do to DNA strands?
in melanocytes: pyrimindine dimers -> formed when cyclobutane rings occur between adjacent, same strand pyrimidines in DNA
- (disrupts p53 gene (tumour supressor))
/
smoking:
causes double stranded breaks and base pair transversions (more deletarious types)