Biology by Bradford
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The subtopic in the middle and nine tasks round it: label three diagrams, complete a table, put a process in order and fill 43 gaps. The whole subtopic is higher level. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
A receptor is a protein with a binding site that fits one particular signalling chemical, its . Binding changes the receptor's , which sets off a pathway: a sequence of responses inside the cell. The acetylcholine receptor is also an ion channel: when it opens, positively charged ions such as diffuse into the cell and change the .
Where a receptor passes through the membrane, its surface has amino acids. A ligand cannot cross the membrane, so it binds outside. Steroid hormones such as oestradiol, progesterone and testosterone pass straight through and bind inside; the activated receptor binds to specific DNA sequences and promotes of the genes there.
1234| Signal | Released by | Acts on |
|---|---|---|
| Hormone | glands | distant cells, carried in the |
| Neurotransmitter | neurons | the next cell, reached by |
| Cytokine | many cells, such as immune cells | cells |
| Calcium ions | channels in membranes | proteins the same cell |
Hormones belong to different chemical groups: epinephrine is an , insulin a , and oestradiol a . Neurotransmitters are just as varied: glutamate is an , the endorphins are , and nitric oxide is a gas. So many different molecules, each with its own receptors, let many separate messages travel at once without being confused.
Binding switches on the receptor's activity inside the cell. A sequence of reactions follows that ends with more carriers in the plasma membrane, so the cell takes in faster.
Each Vibrio fischeri cell releases a little of a signalling chemical. Where cells are few it diffuses away, but where the population is high, as in the light organ of the bobtail squid, its rises past a threshold. It then binds to in the bacteria, which switch on the genes for all at once. This is .
Number the steps in order.
cAMP is the . One epinephrine molecule leads to a great many cAMP molecules, so the signal is . Humans have hundreds of different receptors that work through G proteins.
Oestradiol binds to receptors in cells of the that secrete GnRH. Before ovulation, rising oestradiol makes them secrete more GnRH, which leads through the pituitary to still more oestradiol: the response strengthens the signal, so this is feedback. In feedback the response weakens the signal and a level stays steady: insulin lowers blood glucose, so less insulin is then secreted. Progesterone binds to receptors in cells of the , keeping it thick and ready for an embryo to implant.
A receptor is a protein with a binding site that fits one particular signalling chemical, its ligand. Binding changes the receptor's shape, which sets off a signal transduction pathway: a sequence of responses inside the cell. The acetylcholine receptor is also an ion channel: when it opens, positively charged ions such as sodium diffuse into the cell and change the membrane potential.
Each Vibrio fischeri cell releases a little of a signalling chemical. Where cells are few it diffuses away, but where the population density is high, as in the light organ of the bobtail squid, its concentration rises past a threshold. It then binds to receptors in the bacteria, which switch on the genes for bioluminescence all at once. This is quorum sensing.
| Signal | Released by | Acts on |
|---|---|---|
| Hormone | endocrine glands | distant cells, carried in the blood |
| Neurotransmitter | neurons | the next cell, reached by diffusion |
| Cytokine | many cells, such as immune cells | nearby cells |
| Calcium ions | channels in membranes | proteins within the same cell |
Hormones belong to different chemical groups: epinephrine is an amine, insulin a protein, and oestradiol a steroid. Neurotransmitters are just as varied: glutamate is an amino acid, the endorphins are peptides, and nitric oxide is a gas. So many different molecules, each with its own receptors, let many separate messages travel at once without being confused.
Where a receptor passes through the membrane, its surface has hydrophobic amino acids. A hydrophilic ligand cannot cross the membrane, so it binds outside. Steroid hormones such as oestradiol, progesterone and testosterone pass straight through and bind inside; the activated receptor binds to specific DNA sequences and promotes transcription of the genes there.
cAMP is the second messenger. One epinephrine molecule leads to a great many cAMP molecules, so the signal is amplified. Humans have hundreds of different receptors that work through G proteins.
Binding switches on the receptor's tyrosine kinase activity inside the cell. A sequence of reactions follows that ends with more carriers in the plasma membrane, so the cell takes in glucose faster.
Oestradiol binds to receptors in cells of the hypothalamus that secrete GnRH. Before ovulation, rising oestradiol makes them secrete more GnRH, which leads through the pituitary to still more oestradiol: the response strengthens the signal, so this is positive feedback. In negative feedback the response weakens the signal and a level stays steady: insulin lowers blood glucose, so less insulin is then secreted. Progesterone binds to receptors in cells of the endometrium, keeping it thick and ready for an embryo to implant.