Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Medical Genetics > Lecture 1 - Inheritance > Flashcards

Lecture 1 - Inheritance Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Deoxyribonucleic Acid

A
  • double helix
  • four chemical ‘bases’
  • Adenine, Thymine (2x H bonds)
  • Cytosine, Guanine (3x H bonds)
  • bases are attached to 2x phosphate backbones
  • DNA is tightly packed (space saving)
  • 3.2b bases in the human genome
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

DNA packaging

A
  • DNA+RNA+Protein = Chromatin
  • main chromatin protein: Histones
  • DNA wound around histones 2x = Nucleosome
  • Nucleosomes organised into SOLENOIDS
  • SOLENOIDS loop into chromatin
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Histones

A
  • made up of 8 proteins: H2A, H2B, H3 and H4
  • H1 is a LINKER HISTONE: binds to DNA entry and exit sites of the nucleosome
  • DNA is wound around each histone twice
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Chromatin

A
  • Euchromatin: open, prevalent in parts of the genome that are regularly used
  • Heterochromatin: condensed, not active in expression
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Chromosomes

A
  • two identical chromatids
  • p arm = short, q arm = long
  • centromere in the centre
  • 22 autosomes and 2 sex chromosomes = 24
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Human cells

A
  • Haploid: 23 chromosomes (inc 1 sex chromosome)

- Diploid: 46 chromosomes (inc 2 sex chromosomes)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Genes

A
  • basic physical unit of heredity
  • vary in length: 100s - >2.5m bases
  • approx 20,000-23,000 genes in human genome
  • why fewer genes than expected? alternative splicing, alternative post translational modification
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Genes to proteins

A
  • RNA and protein synthesis
  • transcription - translation
  • degenerate code (more than one codon/aa)
  • non overlapping
  • 64 codons in total
  • stop codons implicated in disease (premature stop)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

When you have a premature stop codon

A

No protein is generated

Nonsense mediated decay, NMD surveillance pathway, cell eliminates incorrect mRNA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Transcription: DNA-> RNA

A
  • RNA polymerase is the main transcription enzyme
  • RNA pol binds to a PROMOTER SEQUENCE near the beginning of a gene (directly or through helper proteins)
  • RNA pol uses one of the DNA strands (the TEMPLATE strand) to make a complementary RNA molecule (PRIMARY RNA)
  • Transcription ends in TERMINATION which depends on stop codon in the DNA sequence
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Difference between DNA and RNA

A
  • RNA single stranded

- Uracil instead of Thymine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

RNA processing

A

Primary RNA is modified before it leaves the nucleus

  • splicing
  • capping
  • polyadenylation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

RNA capping

A
  • 5’ end is capped with 7-methylguanosine

- capping precedes other modifications that protect the mRNA from RNAses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Poly A tails

A
  • protect the 3’ end from phosphatases and nucleases
  • approx 200 nucleotides
  • necessary for nuclear export
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Splicing

A
  • removes introns
  • snRPS spliceosomal proteins (U1, U2, U4, U5, U6) bind to the preMRNA
  • mRNA is removed in a lariat
  • the 2 exons are ligated to make mature mRNA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Translation

A
  • occurs in the cytoplasm on a ribosome
  • Initiation: ribosome connects the mRNA with the first tRNA, translation begins
  • Elongation: amino acids on the tRNAs are linked
  • Termination: finished polypeptide is released and folds
17
Q

Junk DNA

A
  • genes only 2% DNA
  • rest of genome is mostly repetitive sequences
  • can be short repeated segments or long repeats of 1000s of bases repeated 100s of times
  • some junk DNA plays a role in gene regulation
18
Q

Introns/Intragenic regions

A
  • non coding regions within genes

- can regulate expression

19
Q

Intergenic regions

A
  • genome segments between genes

- can regulate expression

20
Q

Mitochondrial DNA (genome)

A
  • 16.6kb codes mtDNA
  • codes 37 genes
  • 2x rRNA
  • 22 transfer RNA
  • 13 protein subunits for enzymes (eg cytb and cyt oxidase - used in oxidative phosphorylation)
  • mtDNA different from nuclear DNA
  • encodes genes necessary for mitochondrial function

Mitochondria inherited exclusively from the oocyte leading to a maternal pattern of inheritance that characterises mitochondrial disorders

21
Q

Mitosis

A
  • rapid cell division leading to an adult human 10(14) somatic cells
  • two identical diploid cells are formed from a single diploid cell
  • Prophase: chromosomes condense, spindle is formed, nuclear envelope disintegrates
  • Metaphase: chromosomes connect to spindle, align on the metaphase plate
  • Anaphase: centromeres split, chromosomes separate and move to opposite poles
  • Telophase: chromosomes cluster at poles and nuclear and organelle envelopes reform
  • Cytokinesis: contractile actin ring divides the cell
22
Q

Meiosis

A
  • gametes produce genetically different organism on fertilisation
  • 2 steps: produced 4 genetically different haploid cells
  • contain a single set of 23 chromosomes
  • spermatogenesis or oogenesis
  • Meiosis I: reduction division, 46 to 23
  • Meiosis II: equational division, 23 to 23 (duplication)
23
Q

Variation during meiosis

A
  • crossing over: of maternal and paternal chromosomes
  • independent assortment: maternal and paternal chromosomes split across the spindle
  • errors in DNA replication
24
Q

Consequences of variation

A
  • changes in protein structure and function
  • natural variatio (eye colour, height etc)
  • inherited/genetic disease (huntingtons, downs, CF)
25
Q

Classification of variation

A
  • size: large and small scale
  • DNA structure: substitution, insertion, deletion
  • protein structure: synonymous, non synonymous (has it changed the a.a. it codes for)
  • change in coding/non coding regions
  • protein function: loss/gain, dominant/negative
26
Q

DNA repair

A
  • germline changes: heritable
  • somatic changes: non heritable
  • mutation drives evolution
27
Q

Crossing over

A
  • homologous chromosomes exchange genetic material at the end of chiasma (prophase I)
  • Resulting chromosomes contain parts of the other pair
28
Q

Independent assortment

A
  • during anaphase I the chromosomes do NOT duplicate
  • only one pair moves to each daughter cell
  • paternal and maternal chromosomes are randomly sorted
  • chromosomes vary from gamete to gamete
29
Q

Meiotic mutations

A
  • Turner’s syndrome XO
  • Down’s syndrome Trisomy 21
  • Edward syndrome Trisomy 18
  • Patau syndrome Trisomy 13

result from non disjunction at meiosis I or II

30
Q

Cell fate

A
  • zygote grows mitotically to the 8 cell stage (embryonic stem cells)
  • they then undergo differentiation
  • all cells have 3 possible destinies:
    1. Remain alive (functioning but not dividing)
    2. Grow and divide
    3. Die (necrosis/apoptosis)
  • these events are controlled by the cell cycle
31
Q

The cell cycle

A
  • interphase: G1, S, G2
  • G1: synthesis of RNA and proteins
  • S: DNA replication
  • G2: some DNA repair, cell contains 2 x 23 pairs of
    chromosomes
  • G0: when the cell stops dividing for a long time
  • G0 length of time varies - liver = 1year, epithelium = 10 hours, muscle and neurones never divide
32
Q

Checkpoints

A
  • in G1, S and G2
  • tumour suppressors act to inhibit cell proliferation
  • oncogenes stiimulate cell growth
  • cyclins and Cdks (transition controlled by phosphorylation, cyclin levels vary in the cycle)
33
Q

S phase

A
  • DNA replication
  • DNA helicase unwinds
  • proteins bind the unwound DNA
  • the leading strand is synthesised 5 to 3 by DNA pol
  • the lagging strand has an RNA primer added by RNA primase
  • RNA primer is then extended by DNA pol into an Okaskai fragment
  • Okasaki fragments joined by DNA ligase
34
Q

Uncontrolled cell division

A
  • cell cycle regulators can become mutated
  • tumour suppressors can become inactive or oncogenes overactive
  • retinoblastoma is caused by a mutation in tumour suppressor RB1
  • Li Fraumeni multi organ cancer syndrome caused by mutations in tumour suppressor p53
  • lung cancers often have mutation in kras (oncogene)
35
Q

Cell death

A
  • apoptosis (webbing between fingers)

- necrosis (trauma, infection)

36
Q

Roles of apoptosis

A
  • shaping tissues and organs
  • immune system: ineffective or self reactive T cells removed
  • cancer: too little apoptosis
  • too much apoptosis: neurodegenerative disease

Medical Genetics (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions