KA 5 Flashcards
How do multicellular organisms signal between cells?
They use extracellular signaling molecules like steroid hormones, peptide hormones, and neurotransmitters.
What are receptor molecules?
Receptor molecules are proteins on target cells with a binding site for a specific signaling molecule. Binding causes a conformational change and initiates a cellular response.
What determines the ability of a cell to respond to a signal?
Cells can only respond to specific signals if they have the receptor for that signal.
Can signaling molecules have different effects on different cell types?
Yes, signaling molecules can produce different effects due to differences in the intracellular signaling pathways of various cell types.
How do hydrophobic signaling molecules work?
Hydrophobic signaling molecules can diffuse through the phospholipid bilayer, bind to intracellular receptors, and affect gene expression by acting as transcription factors.
What are transcription factors?
Transcription factors are proteins that, when bound to DNA, can either stimulate or inhibit the initiation of transcription, affecting gene expression.
What are examples of hydrophobic signaling molecules?
Steroid hormones like oestrogen and testosterone are examples of hydrophobic signaling molecules.
How do steroid hormones affect gene expression?
Steroid hormones bind to specific receptors, form a hormone-receptor complex, and move to the nucleus, where they bind to hormone response elements (HREs) on DNA, influencing transcription.
How do hydrophilic signaling molecules work?
Hydrophilic signaling molecules bind to transmembrane receptors on the cell surface, which changes the receptor’s conformation and transduces the signal into the cell.
What happens after a ligand binds to a transmembrane receptor?
The receptor undergoes a conformational change that converts the extracellular binding event into an intracellular signal, altering the behavior of the cell.
What is the role of G-proteins in signal transduction?
G-proteins relay signals from activated receptors to target proteins, such as enzymes and ion channels.
What is a phosphorylation cascade?
A phosphorylation cascade involves a series of kinase activations that amplify the signal, activating multiple intracellular pathways.
How does insulin signaling work?
Insulin binds to its receptor, triggering a phosphorylation cascade that eventually leads to the transport of GLUT4 (glucose transporters) to the cell membrane for glucose uptake.
What causes diabetes mellitus?
Type 1 diabetes is caused by failure to produce insulin, while type 2 is caused by loss of receptor function and is often associated with obesity.
How does exercise affect glucose uptake in type 2 diabetes?
Exercise triggers the recruitment of GLUT4 transporters, improving glucose uptake into fat and muscle cells, which can help in type 2 diabetes.
What is the resting membrane potential?
The resting membrane potential is the state where there is no net ion flow across the membrane, with the inside of the cell being more negative than the outside.
What is an action potential?
An action potential is a wave of electrical excitation that travels along the neuron’s membrane, causing rapid changes in membrane potential.
How does neurotransmitter binding trigger an action potential?
Binding of a neurotransmitter opens ligand-gated ion channels, causing depolarization. If the threshold is reached, voltage-gated sodium channels open, generating an action potential.
How is the resting membrane potential restored?
After depolarization, voltage-gated potassium channels open to restore the resting membrane potential, and the sodium-potassium pump restores ion gradients.
What is the role of the sodium-potassium pump in restoring membrane potential?
The sodium-potassium pump restores sodium and potassium ions to their resting concentrations after an action potential, maintaining the electrochemical gradients.
What is the function of the retina in the eye?
The retina detects light and contains two types of photoreceptor cells: rods (for dim light) and cones (for color vision).
How do rods and cones differ?
Rods function in dim light and do not detect color, while cones are responsible for color vision and function in bright light.
What is rhodopsin?
Rhodopsin is the retinal-opsin complex in rod cells that absorbs light and initiates a signaling cascade.
How does photoexcited rhodopsin activate G-proteins?
Photoexcited rhodopsin activates transducin, a G-protein, which activates the enzyme phosphodiesterase (PDE), leading to a decrease in cGMP levels.
What does the reduction in cGMP do in rod cells?
The reduction in cGMP causes the closure of ion channels, triggering nerve impulses in neurons in the retina.
How does rod cell signaling achieve amplification?
A single photoexcited rhodopsin activates hundreds of G-proteins, amplifying the response to low light intensities.
How do cone cells detect different wavelengths of light?
In cone cells, different forms of opsin combine with retinal, each sensitive to specific wavelengths (e.g., red, green, blue, or UV light).
