hormones Flashcards
hormones
chemical messengeers released directly into the blood from endocrine glands
produced either in an inactive form or packaged within secretory vesicles by the golgi apparatus
vesicles fuse with cell surface membrane, releasing their contents by exocytosis
only affect specific target cells- modifying their activity
pituitary gland
growth hormone, follicle-stimulating hormone, antidiuretic hormone
stimulates growth
controls testes and ovaries
causes reabsorption of water in kidneys
thyroid gland
thryoxine
raises basal metabolic rate
adrenal gland
adrenaline
raises BMR
dilates blood vessels
prepares the body for action
ovary
oestrogen
promotes development of ovaries and female secondary sexual characteristics
testis
testosterone
promotes development of male secondary sexual characteristics
how hormones affect cells
only affect specific target cells- modifying their activity
carried in the bloodstream
enter target cells/ bind to complementary receptor molecules on the outside of cell membranes
peptide hormones
protein chains (made of amino acids)
unable to pass through cell membranes as they are charged
bind to a receptor on the cell membrane
this activates another molecule in the cytoplasm- a second messenger
second messenger brings about chemical changes in the cell by affecting gene transcription
peptide hormone example
EPO
human growth hormone
insulin
steroid hormones
formed from lipids and have complex ring structures
pass through cell membrane and directly bind to receptor molecule in cytoplasm
testosterone
steroid hormone
passes through cell membrane and binds directly to a receptor molecule within cytoplasm
hormone-receptor complex brings about characteristic responses- resulting from effect on transcription
hormone-receptor complex functions as a transcription factor- switching enzyme synthesis on or off
how do transcription factors work
transcription factors bind to DNA
resulting transcription initiation complex binds to a section of DNA adjacent tot he gene to be transcribed (promotor region)
once this has correctly attached to DNA, transcription will start
creation of transcription factors
most created in an inactive form
then converted to active form by action of hormones/ growth factors/ other molecules
gene remains switched off until all transcription factors are present and in their active forms
transcription-initiation complex can then form and bind to promotor region
preventing transcription
prevented by repressor molecules attaching to the DNA of the promoter region
blocks attachment sites for transcription factors
prevents formation of transcription-initiation complex
protein repressor molecules may also attach to transcription factors themselves- preventing them from forming transcription initiation complex
repressor molecules may be inactive transcription factors
effect of repressor molecules
whichever mechanism results in gene being switched off and not transcribed within specific cell
control of transcription initiation is very important in determining whether a gene is expressed or not
activator molecules
stimulate the binding of the transcription initiation complex
