Chapter 4 Flashcards
What is the importance of selectively permeable membranes?
They separate internal and external contents while allowing specific exchange of molecules/ions.
What are the qualities required for a barrier in cellular membranes?
- Impermeable to most molecules and ions
- Ability to exchange specific molecules/ions
- Insoluble in water
- Permeable to water
What are the main components of a cellular membrane?
- Phospholipids
- Glycolipids
- Sterols (cholesterol, ergosterols, phytosterols)
- Membrane proteins
What types of membrane proteins exist?
- Integral proteins (transmembrane)
- Peripheral membrane proteins
What is the Fluid Mosaic Model of membranes?
It describes membranes as fluid lipid bilayers with embedded proteins that float freely.
True or False: Membranes are rigid structures.
False
What does polarity in water molecules refer to?
Uneven distribution of charge due to electronegative oxygen and electropositive hydrogen.
What does hydrophilic mean?
Water-loving substances that can form hydrogen/ionic bonds with water.
What does hydrophobic mean?
Water-fearing substances that do not dissolve in water.
What is a solvent?
A fluid in which another substance (solute) can be dissolved.
What is the significance of hydrophobic interactions?
They drive the folding of molecules, assembly of structures, and membrane organization.
What are phospholipids characterized by?
They are amphipathic with a hydrophilic head and two hydrophobic tails.
How does temperature affect membrane fluidity?
- Low temperature: membrane becomes viscous
- High temperature: membrane becomes too fluid
What role do desaturases play in membrane fluidity?
They produce unsaturated fatty acids, allowing regulation of membrane fluidity.
What do sterols do in membranes at high temperatures?
They restrain movement of lipids, preventing excessive fluidity.
What do sterols do in membranes at low temperatures?
They disrupt fatty acid associations, slowing the transition to a semisolid state.
What can organisms change to optimize membrane fluidity?
- Fatty acid desaturation
- Cholesterol content
What are integral membrane proteins?
Proteins embedded in the phospholipid bilayer, often coiled into alpha helices.
What are peripheral membrane proteins?
Proteins located on the membrane surface, held by noncovalent bonds.
What is passive transport?
Movement of molecules across a membrane without using chemical energy.
What drives passive transport?
Diffusion, the net movement from higher to lower concentration.
What is simple diffusion?
Passive transport of small uncharged molecules without a transporter.
What factors impede the crossing of membranes for larger or charged molecules?
Their size and charge may strongly hinder their movement.
What are the two types of passive transport?
- Simple diffusion
- Facilitated diffusion
Define simple diffusion.
Movement of molecules across a membrane without involvement of a transporter.
What factors influence simple diffusion?
- Molecular size
- Lipid solubility
Which types of molecules move rapidly through simple diffusion?
Small uncharged molecules.
What is facilitated diffusion?
Diffusion of molecules across a membrane with the help of a transporter.
What is osmosis?
Passive diffusion of water molecules across a selectively permeable membrane.
In osmosis, water moves from a _______ solution to a _______ solution.
hypotonic; hypertonic
What occurs when solutions on each side of a membrane are isotonic?
No osmotic movement of water in either direction.
What is active transport?
Transport of molecules across a membrane against a concentration gradient.
What is required for active transport?
A direct or indirect input of energy derived from ATP hydrolysis or concentration gradients.
What are the two kinds of active transport?
- Primary active transport
- Secondary active transport
Define primary active transport.
The same protein that transports the molecules also hydrolyzes ATP to directly power the transport.
What is the function of the Na+/K+ pump?
Moves 3 Na+ out and 2 K+ in for every pump cycle, creating a negative membrane potential.
What is secondary active transport?
Transport that is indirectly driven by ATP hydrolysis using a favorable concentration gradient of ions.
What are the two mechanisms of secondary active transport?
- Symport
- Antiport
What is exocytosis?
Process where a secretory vesicle carries materials through the cytoplasm and fuses with the plasma membrane to release contents.
What is endocytosis?
Process where materials outside the cell are enclosed in the plasma membrane, forming an endocytic vesicle.
Define pinocytosis.
Endocytosis of solute and water molecules; also known as ‘cell drinking’.
What is receptor-mediated endocytosis?
Process where molecules bind to receptor proteins, forming a coated pit that pinches off to form an endocytic vesicle.
Define phagocytosis.
Endocytosis of large aggregates of molecules or whole cells; also known as ‘cell eating’.
What are the essential elements for cell signaling?
- Signal
- Receptor
- Signal Transduction
- Response
- Termination
What is signal transduction?
The process of transferring the presence of a signal through the cell to elicit a response.
What happens during the termination phase of cell signaling?
The cell turns off the response once the signal is gone.
What are the three stages of signal transduction?
- Reception
- Transduction
- Response
True or False: Only cells with a receptor for a specific signal can respond to that signal.
True
What type of receptors are involved in responses to steroid hormones?
Intracellular receptors.
What are the three common stages of signal transduction?
Reception, transduction, and response
What happens during the receptor activation stage in cell signaling?
The signal binds to a receptor, activating it
What is the purpose of signal transduction in cell signaling?
To transmit the signal to the interior of the cell
What occurs during the response stage of signal transduction?
The cell activates an enzyme or turns on gene transcription
What is the termination stage in signal transduction?
The response is terminated to allow for new signals
Fill in the blank: The binding of a signal molecule to a plasma membrane receptor activates a _______.
signalling cascade
True or False: The signal molecule enters the cell during signal transduction.
False
What role do protein kinases play in signal transduction?
They transfer a phosphate group from ATP to target proteins
What is the function of added phosphate groups on target proteins?
They stimulate or inhibit the activities of target proteins
What do protein phosphatases do in the signal transduction process?
They remove phosphate groups from target proteins
Fill in the blank: Some signalling cascades involve the production of _______ messengers.
second
What is a phosphorylation cascade?
A series of phosphorylation reactions catalyzed by protein kinases
How does amplification occur in signal transduction pathways?
Each activated enzyme can activate hundreds of proteins in the next step
What is the effect of just a few extracellular signal molecules in a signal transduction pathway?
They can produce a full internal response
What is the first messenger in the example of glycogen breakdown stimulation?
Epinephrine
How does epinephrine affect blood glucose levels?
It leads to an increase in blood glucose
What physiological responses are included in the ‘fight or flight’ response?
Burst of energy, increased heart rate, dilated pupils
How does one signal lead to multiple responses?
Through the activation of different pathways or target proteins
