Cells

Question 1

What does the fluid mosaic model of membrane structure depict?

Answer 1

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.

Question 2

What is the thickness range of the plasma membrane?

Answer 2

7-10 nm

This measurement indicates the exceedingly thin nature of the plasma membrane.

Question 3

What primarily composes the lipid bilayer of the plasma membrane?

Answer 3

Phospholipids, with smaller amounts of cholesterol

The lipid bilayer forms the basic ‘fabric’ of the membrane.

Question 4

What is the orientation of the hydrophilic heads of phospholipids in the membrane?

Answer 4

They lie on both the inner and outer surfaces of the membrane

This orientation is due to their attraction to water.

Question 5

What do the nonpolar tails of phospholipids do in the membrane?

Answer 5

They line up in the center of the membrane, avoiding water

This creates a sandwich-like structure in biological membranes.

Question 6

What is the general structure of all biological membranes?

Answer 6

Two parallel sheets of phospholipid molecules lying tail to tail

The polar heads are bathed in water on either side.

Question 7

What property of phospholipids encourages biological membranes to self-assemble?

Answer 7

Their self-orienting property

This property helps membranes to reseal themselves when torn.

Question 8

How does the plasma membrane’s consistency compare to everyday substances?

Answer 8

It is similar to olive oil

This indicates the dynamic fluid nature of the plasma membrane.

Question 9

How do phospholipids move within the plasma membrane?

Answer 9

They move freely from side to side, parallel to the membrane surface

They rarely flip-flop or move between the bilayer halves.

Question 10

What percentage of membrane lipid is cholesterol?

Answer 10

20%

Cholesterol plays a role in stiffening the membrane.

Question 11

What are the two distinct populations of proteins found in the plasma membrane?

Answer 11

Integral and peripheral proteins

Integral proteins are embedded in the membrane, while peripheral proteins are attached to the surface.

Question 12

What role do proteins play in the plasma membrane?

Answer 12

They allow the cell to communicate with its environment

Proteins are responsible for most specialized membrane functions.

Question 13

True or False: Proteins make up about half of the plasma membrane by mass.

Answer 13

True

This highlights the significant role of proteins in membrane structure.

Question 14

Fill in the blank: The polar heads of phospholipids are attracted to _______.

Answer 14

water

This attraction is due to the hydrophilic nature of the heads.

Question 15

What happens to the inward-facing and outward-facing surfaces of the plasma membrane?

Answer 15

They differ in the kinds and amounts of lipids they contain

These variations help determine local membrane structure and function.

Question 16

What are integral proteins?

Answer 16

Integral proteins are firmly inserted into the lipid bilayer

Question 17

What type of proteins span the entire membrane and protrude on both sides?

Answer 17

Transmembrane proteins

Question 18

What regions do all integral proteins have?

Answer 18

Both hydrophobic and hydrophilic regions

Question 19

What is the function of transmembrane proteins involved in transport?

Answer 19

They form channels or pores for small, water-soluble molecules or ions to move through

Question 20

Some transmembrane proteins act as what type of molecules?

Answer 20

Enzymes or receptors for hormones

Question 21

What is signal transduction?

Answer 21

The process by which receptors relay messages to the cell interior

Question 22

How do peripheral proteins differ from integral proteins?

Answer 22

Peripheral proteins are not embedded in the lipid bilayer

Question 23

How do peripheral proteins attach to the membrane?

Answer 23

They attach loosely to integral proteins or have a hydrophobic region that anchors them

Question 24

What role do peripheral proteins play in the cell?

Answer 24

They help support the membrane and can act as enzymes or motor proteins

Question 25

What are glycolipids?

Answer 25

Lipids with sugars attached

Question 26

What replaces the phosphate head group in glycolipids?

Answer 26

A carbohydrate

Question 27

What is the glycocalyx?

Answer 27

The fuzzy, sticky, carbohydrate-rich area at the cell surface

Question 28

What is the function of the glycocalyx?

Answer 28

It provides identity molecules for cell recognition

Question 29

True or False: Glycoproteins are proteins with sugars attached.

Answer 29

True

Question 30

What are glycoproteins secreted by the cell used for?

Answer 30

They enrich the glycocalyx

Question 31

Fill in the blank: The extracellular surface of the membrane is decorated with short branching _______.

Answer 31

carbohydrates

Question 32

What helps change cell shape during cell division and muscle cell contraction?

Answer 32

Motor proteins

Question 33

What are cell junctions?

Answer 33

Specialised structures that allow neighbouring cells to adhere to and communicate with each other.

Question 34

What are the three types of cell junctions?

Answer 34

* Tight junctions * Desmosomes * Gap junctions

Question 35

What is the primary function of tight junctions?

Answer 35

To form an impermeable junction that prevents molecules from passing through the extracellular space between adjacent cells.

Question 36

How do tight junctions resemble a Ziploc bag?

Answer 36

They consist of a series of integral protein molecules that fuse together, forming a seal around the cell.

Question 37

What is an example of where tight junctions are important?

Answer 37

In epithelial cells lining the digestive tract to keep digestive enzymes and microorganisms in the intestine.

Question 38

True or False: All tight junctions are impermeable.

Answer 38

False

Question 39

What are desmosomes often referred to as?

Answer 39

"Binding bodies"

Question 40

What is the role of desmosomes?

Answer 40

To serve as anchoring junctions that prevent the separation of adjacent cells.

Question 41

What are the structures that connect adjacent cells in desmosomes?

Answer 41

Thin linker protein filaments called cadherins.

Question 42

What do desmosomes contribute to within tissues?

Answer 42

A continuous internal network of strong fibers that distribute tension throughout a cellular sheet.

Question 43

In which types of tissues are desmosomes abundant?

Answer 43

Tissues subjected to great mechanical stress, such as skin and heart muscle.

Question 44

What is a gap junction?

Answer 44

A communicating junction between adjacent cells.

Question 45

What connects cells at gap junctions?

Answer 45

Hollow cylinders called connexons composed of transmembrane proteins.

Question 46

What types of molecules can pass through gap junctions?

Answer 46

* Ions * Simple sugars * Other small molecules

Question 47

Where are gap junctions particularly important?

Answer 47

In electrically excitable tissues, such as the heart and smooth muscle.

Question 48

What is the significance of ion passage through gap junctions?

Answer 48

It helps synchronize electrical activity and contraction in muscle tissues.