3 Flashcards
how many classes of steroid hormones are there?
5 major classes
mineralocorticoids?
increase blood volume and pressure
e.g. aldosterone
glucocorticoids?
promote high blood glucose
e.g. cortisol
androgens?
development of secondary female sexual characteristics
e.g. testosterone
oestrogen?
development of secondary sexual characteristics
e.g. estradiol
progestogens?
maintenance of pregnancy
e.g. progesterone
steroid hormone receptors are also called
ligand-activating transcription factor proteins
consists of dimers, each with 3 domains
what is the zinc finger domain?
binds zinc ions between alpha helix and beta pleated sheets to form finger like structure
what amino acids is the zinc finger rich in?
basic AAs = cys, arg, lys
well suited to bind acidic DNA
how many zinc fingers does a receptor dimer have?
2
1st = confers specificity of binding
2nd = stabilises dimer structure
what are SREs?
specific response elements
they are labels that identify genes as targets for transcription factors
2 half sites in DNA sequence, what do they bind?
each half binds the Zn finger domain from one monomer of SHR dimer
can be a mirror image (homodimer) or direct repeats (heterodimer)
response elements are transcriptional enhancers, what do they do?
SHRs move to nucleus
they unravel chromosomes by recruiting HATs or removing HDACs
then bind to SRE DNA sequence
forms a complex, RNA polymerase is recruited, promoter is activated and transcription is initiated
what are gated channels?
receptors linked to ion channels that open in response to external stimuli / ligands
consequences of changes in membrane permeability:
- changes in pH or oxidation state within cells (H+)
- supplying proteins with ionic co-factors (Fe+)
- supplying cells with energy (glucose)
- changes in potential difference across membrane (Na+ / K+)
presence of Ca2+ within cells can trigger…
changes in enzymatic activity / protein movement and behaviour in cells
cells allow Ca2+ concs to:
rise to levels at which proteins / phospholipids bind
trigger changes in conformation and function
reduced back to levels where the process can be reversed
the Ca2+ system:
stimulation of cell
1. entry of Ca2+ into localised parts of cell
2. binding of Ca2+ to biological molecules
cellular responses
3. expulsion of Ca2+ from cell
cell recovery
Ca2+ forms insoluble complexes with…
and why?
phosphorylated and carboxylated compounds
so cytoplasmic levels of Ca2+ are kept low to avoid precipitation
what organelle is a Ca2+ store?
ER - it has a larger surface area than PM, it mops and pumps Ca2+ that has leaked into cytoplasm
how many parallel Ca2+ mobilisation systems do cells have?
2
1st = Ca2+ released into cytoplasm
2nd = Ca2+ removed from cytoplasm
Ca2+ released into cytoplasm via…
- channels in PM
- channels in ER membrane
Ca2+ removed from cytoplasm via…
- PMCA pump in PM
- SERCA pump in ER membrane
what is IP3?
- 2nd messenger
- diffuses into cytoplasm and acts as ligand to release Ca2+ from internal stores (ER)
