Cells Flashcards
What does the fluid mosaic model of membrane structure depict?
The plasma membrane as a thin structure composed of a lipid bilayer with proteins dispersed in it
The model is characterized by a constantly changing mosaic pattern formed by proteins.
What is the thickness range of the plasma membrane?
7-10 nm
This measurement indicates the exceedingly thin nature of the plasma membrane.
What primarily composes the lipid bilayer of the plasma membrane?
Phospholipids, with smaller amounts of cholesterol
The lipid bilayer forms the basic ‘fabric’ of the membrane.
What is the orientation of the hydrophilic heads of phospholipids in the membrane?
They lie on both the inner and outer surfaces of the membrane
This orientation is due to their attraction to water.
What do the nonpolar tails of phospholipids do in the membrane?
They line up in the center of the membrane, avoiding water
This creates a sandwich-like structure in biological membranes.
What is the general structure of all biological membranes?
Two parallel sheets of phospholipid molecules lying tail to tail
The polar heads are bathed in water on either side.
What property of phospholipids encourages biological membranes to self-assemble?
Their self-orienting property
This property helps membranes to reseal themselves when torn.
How does the plasma membrane’s consistency compare to everyday substances?
It is similar to olive oil
This indicates the dynamic fluid nature of the plasma membrane.
How do phospholipids move within the plasma membrane?
They move freely from side to side, parallel to the membrane surface
They rarely flip-flop or move between the bilayer halves.
What percentage of membrane lipid is cholesterol?
20%
Cholesterol plays a role in stiffening the membrane.
What are the two distinct populations of proteins found in the plasma membrane?
Integral and peripheral proteins
Integral proteins are embedded in the membrane, while peripheral proteins are attached to the surface.
What role do proteins play in the plasma membrane?
They allow the cell to communicate with its environment
Proteins are responsible for most specialized membrane functions.
True or False: Proteins make up about half of the plasma membrane by mass.
True
This highlights the significant role of proteins in membrane structure.
Fill in the blank: The polar heads of phospholipids are attracted to _______.
water
This attraction is due to the hydrophilic nature of the heads.
What happens to the inward-facing and outward-facing surfaces of the plasma membrane?
They differ in the kinds and amounts of lipids they contain
These variations help determine local membrane structure and function.
What are integral proteins?
Integral proteins are firmly inserted into the lipid bilayer
What type of proteins span the entire membrane and protrude on both sides?
Transmembrane proteins
What regions do all integral proteins have?
Both hydrophobic and hydrophilic regions
What is the function of transmembrane proteins involved in transport?
They form channels or pores for small, water-soluble molecules or ions to move through
Some transmembrane proteins act as what type of molecules?
Enzymes or receptors for hormones
What is signal transduction?
The process by which receptors relay messages to the cell interior
How do peripheral proteins differ from integral proteins?
Peripheral proteins are not embedded in the lipid bilayer
How do peripheral proteins attach to the membrane?
They attach loosely to integral proteins or have a hydrophobic region that anchors them
What role do peripheral proteins play in the cell?
They help support the membrane and can act as enzymes or motor proteins
What are glycolipids?
Lipids with sugars attached
What replaces the phosphate head group in glycolipids?
A carbohydrate
What is the glycocalyx?
The fuzzy, sticky, carbohydrate-rich area at the cell surface
What is the function of the glycocalyx?
It provides identity molecules for cell recognition
True or False: Glycoproteins are proteins with sugars attached.
True
What are glycoproteins secreted by the cell used for?
They enrich the glycocalyx
Fill in the blank: The extracellular surface of the membrane is decorated with short branching _______.
carbohydrates
What helps change cell shape during cell division and muscle cell contraction?
Motor proteins
What are cell junctions?
Specialised structures that allow neighbouring cells to adhere to and communicate with each other.
What are the three types of cell junctions?
- Tight junctions
- Desmosomes
- Gap junctions
What is the primary function of tight junctions?
To form an impermeable junction that prevents molecules from passing through the extracellular space between adjacent cells.
How do tight junctions resemble a Ziploc bag?
They consist of a series of integral protein molecules that fuse together, forming a seal around the cell.
What is an example of where tight junctions are important?
In epithelial cells lining the digestive tract to keep digestive enzymes and microorganisms in the intestine.
True or False: All tight junctions are impermeable.
False
What are desmosomes often referred to as?
“Binding bodies”
What is the role of desmosomes?
To serve as anchoring junctions that prevent the separation of adjacent cells.
What are the structures that connect adjacent cells in desmosomes?
Thin linker protein filaments called cadherins.
What do desmosomes contribute to within tissues?
A continuous internal network of strong fibers that distribute tension throughout a cellular sheet.
In which types of tissues are desmosomes abundant?
Tissues subjected to great mechanical stress, such as skin and heart muscle.
What is a gap junction?
A communicating junction between adjacent cells.
What connects cells at gap junctions?
Hollow cylinders called connexons composed of transmembrane proteins.
What types of molecules can pass through gap junctions?
- Ions
- Simple sugars
- Other small molecules
Where are gap junctions particularly important?
In electrically excitable tissues, such as the heart and smooth muscle.
What is the significance of ion passage through gap junctions?
It helps synchronize electrical activity and contraction in muscle tissues.
