IMMS Flashcards
what is lipofuscin?
a yello-brown pigment granule that is made up of residues from lysosomal digestion
it is thought to be a ‘wear and tear’ pigment
Cell membrane constituents
- phospholipids
- cholesterol
- membrane proteins
- carbohydrates
- if attached to lipids called glycolipids
- if attached to proteins called glycoproteins
Membrane composition by mass
- 50% proteins
- 40% lipids
- 10% carbs
Functions of the cell membrane
- anchor the cell to the ECM
- connect cells together
- regulate incoming and outgoing substances
- recognise chemical messangers
- form distinct border of cell
three types of cell junctions:
- Anchoring junctions
- Gap junctions
- Tight junctions
Three types of anchoring Junctions
Desmosomes
Hemidesmosomes
Adherens
Parts of a G protein coupled receptor
- the receptor
- alpha
- beta
- gamma
- an enzyme that makes the secondary messanger
Desmosomes: can you draw the diagram?
Tight junctions can you draw the diagram
Gap junctions - can you draw the diagram?
only small molecules and ions can pass through - not proteins
primary and secondary active transport
- primary: energy derived directly from ATP
- secondary: energy derived from coupling the transport of a substrate down its concentration gradient
3 different types of endocytosis
- Phagocytosis
- pseudopodia engulf foreign particles in a phagosome
- Pinocytosis
- Extracellular fluid is engulfed in an invagination of the membrane and fluid is taken into the cell
- Receptor mediated
- Receptor binding causes an invagination of a coated pit
- When vesicle is taken in to the cell it contains both the particle and its receptors
4 Glucose transporters
- GLUT1:
- bb barrier
- erythrocytes
- GLUT2:
- renal tubular cells
- pancreatic beta cells
- basolateral surface of intestinal epithelia
- Liver
- bidirectional to release G during gluconeogenesis and take it up durign glycolysis
- GLUT3:
- neurons
- GLUT4:
- adipose tissue
- striated muscle
Polymorphism Definition
- Frequently hereditary variations at a locus - not pathogenic
Hemizygous Definition
- When there is no allelic counterpart to a gene
- e.g. X chromosome genes in a male
What is imprinting?
- Mostly both alleles of a gene are expressed at once
- Sometimes they’re imprinted meaning that only one allele is expressed
- The expression of a gene depends on the parent who passed that gene on
- It’s a normal part of development
- prader-willi and angelman show this specific inheritance pattern because of imprinting
how to notate a translocation from band 24 of the q arm of chromosome 1 to band 12 on the q arm of chromosome 2?
t(1;2)(q24;p12)
How to notate an inversion between band 11 on the q arm of chormosome 7 and band 21 on the q arm of chromosome 7
inv(7)(q11;q21)
how to notate a duplication of a section of chromosome 11 between band 14 on the p arm and band 15 on the p arm?
dup(11)(p14;p15)
How to denote a deletion of a section of the q arm of chromosome 22 between band 11 and 12
del(22)(q11;q12)
FISH
- Fluorescence in situ hybridisation
- use fluorescent probe to hybridise with complementary sequence and visualise any rearrangements or deletions
microarrays are now used because they have better resolution
<200kb
Cell cycle very simply
Stages of Mitosis
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
Prophase
- centrosomes migrate to opposite poles of the cell
- chromatin condenses
prometaphase
- Nuclear membrane breaks down
- microtubules from the centrosomes attach to chromatids
Metaphase
- Chromasomes line up allong the equatorial plane
Anaphase
- sister chromatids seperate and are pulled to opposite poles
Telophase
- nuclear membrane reforms
- chromosomes unfold
- cytokinesis begins
When do meiotic divisions commence in males
- they start at puberty
when does meiosis I occur in females
- oogonia enter prophase I by 8th month of intrauterine life
- meiosis I is only completed at ovulation 10-50 years later
when is meiosis II completed in females?
- it is completed only after fertilisation producing one fertilized mature ovum and one polar body (the 3rd polar body to be produced)
Mendel’s 3 laws
- Law of segregation
- Law of independant assortment
- Law of dominance
Mendel’s 1st Law
- the law of segregation
- “During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.”
Mendel’s 2nd Law
- the law of independant assortment
- “Genes for different traits can segregate independently during the formation of gametes.”
Mendel’s 3rd Law
- The law of dominance
- “Some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele.”
When does the non-dysjunction happen in trisomy 21?
- mostly non-dysjunction at maternal Meiosis I
- sometimes at maternal Meiosis II
- very very rarely it’s paternal non-dysjunction
Gonadal Mosaicism
- two populations of precursor germline cells (that go on to produce sperm or ova)
- one of these populations is mutated
- therefore the baby may have a genetic disease but the parent is fine
what is starch?
- A combination of:
- amylose (glucose 1-4 bonds)
- amylopectin (1-4 and 1-6 side chains)
- branched
Glycogen
- Glucose polymer storage in animals
- 1-4 glycosidic bonds and 1-6 branches
- so just like amylopectin but glycogen has more branches
- NB glycogenin is needed to prime the very beginning polymerisations in glycogen production
Steroids: basic structure
- the steroid nucleus is 17 carbon atoms bonded into four rings
- rings A,B and C are six member (cyclohexane) rings
- ring D is a five member ring (cyclopentane)
- carbon 17 on ring D binds to the variable group
Amino Acids
- A central carbon bound to a carboxyl group, an amino group, a hydrogen and an R group
- change charge depending on solution they’re in
- make polypeptides by making peptide bonds
- proteins are always written N terminus to C terminus
Purines and Pyrimidines
- Purines have two rings
- Adenine
- Guanine
- Pyrimidines only have one ring
- Uracil
- Cytosis
- Thymine
number of bonds in base pairs
- Cytosine –> Guanine
- three bonds
- Thymine –> Adenine
- two bonds
where are disulphide bonds typical
between cysteine residues
The alpha helix
- A secondary structure
- helix formed by
- H bonds between carbonyl group of one amino acid and the amino group of the amino acid 4 residues along
- R groups look outwards
- Proline can’t do this cause of its R group so it forms a kink
Beta sheet
- formed by H bonds between linear regions of polypeptide chains
- this can be between the same polypeptide or between different polypeptides
- chains can e parallel or antiparallel
what is an isoenzyme
two or more enzymes that have identical function but different structure
Michaelis Menten Equation - can you draw the graph
- Vi = initial velocity
- Km = the substrate concentration when V is 1/2 Vmax
What is Heme
- non-protein part of haemoglobin
- it is a porphyrin ring with a central Fe
- This Fe can bind O2
haemoglobin
- the quaternary structure has four globular subunits
- each subunit can carry one O2
Red blood cells in the tissues
- CO2 from tissues enters the RBC
- it combines with H2O and (via carbonic anhydrase) it forms carbonic acid
- carbonic acid dissociates, releasing protons (and HCO3-)
- the protons combine with HbO2 and kick off the O2
- O2 is released into the tissues
- this is why the curve shifts to the right when it’s acidic
- in acidic media, high protonation inhibits O2 binding
Red blood cells in the lungs
- O2 enters the red blood cells
- at such a high pO2 it binds the protonated Hb (HHb) and kicks off the proton
- the proton combines with bicarbonate (HCO3-) forming carbonic acid
- carbonic acid is cleaved by carbonic anhydrase into CO2 and H2O
- the CO2 is exhaled
How does the temperature and arterial carbon dioxide influence the oxygen dissociation curve
Simple antibody structure
which way does DNA polymerase go?
- it reads the transcript 3’ to 5’ but it prints 5’ to 3’
how much is a kilodalton
- 1000 daltons
- 1000 atomic mass units
- one dalton is the mass of one hydrogen atom
start codon
AUG
remember there aren’t any start codons in DNA, only in mRNA
what is haploinsufficiency?
this is when a pathway is very sensitive to the amount of gene product produced so a loss of function mutation can be inherited in a dominant pattern
haploinsufficiency = half is not enough
stop codons
UGA, UAG, UAA
remember: there aren’t any start codons in DNA they’re only in DNA
Initiating transcription
- we need heterochromatin to turn to euchromatin
- TFs bind promotor sequences which are just 5’ of the first exon
- transcription complex forms at the TATA box (just 5’ of the first exon)
- the helix opens and the DNA seperates
- RNA polymerase II starts to build mRNA
Name a disease caused by a deletion mutation
- duchennes muscular dystrophy
- caused by an out of frame deletion which results in a severely truncated dystrophin protein
- this causes progressive muscle damage in boys
- the much milder becker musclular dystrophy is caused by an in frame deletion
Splice site variations
- splice acceptor sites are either side of the intron that should be excluded
- remember: coding exons are INterupted by INtrons
- if these sites are mutated then splicing won’t happen properly and this will result in an included intron
- this will likely have an effect on protein function
missense mutation
- a point mutation that results in a different amino acid
Non-sense mutation
- out of frame mutation causes a premature stop codon
what is allelic heterogeneity
- it is when many different variants in one gene can cause the same disease
- this is seen with cystic fibrosis