Eukaryotic Cell Structure (Tutorial #6)

Question 1

What are the four general functions of cell membranes?

Answer 1

1. semi-permeable barrier for the cell
2. semi-permeable barrier for organelles
3. regulate the transport of molecules
4. receives signals

Question 2

Explain the fluid-mosaic model of membrane structure.

Answer 2

membranes are organized as a lipid bilayer with embedded proteins

Question 3

What is the most common type of lipid in cell membrane?

Answer 3

phospholipid

Question 4

Define amphipathic.

Answer 4

has both hydrophilic and hydrophobic characteristics

Question 5

What components of a cell membrane are amphipathic?

Answer 5

• phospholipids (hydrophobic tails at the interior of the membrane and hydrophilic heads that face outward towards the inter and extracellular environments)
• trans-membrane proteins

Question 6

Define selective permeability.

Answer 6

Some substances can readily pass through the phospholipid bilayer (non-polar molecules, small molecules, and lipids) while others cannot readily pass through the bilayer and must cross through a transport protein (polar, large, and charged molecules)

Question 7

What do aquaporins do?

Answer 7

Facilitate the transport of water molecules across the cell membrane.

Question 8

Define active transport.

Answer 8

A type of transport that requires some type of input of metabolic energy.

Question 9

Define passive transport.

Answer 9

A type of transport that does not require any energy.

Question 10

What are the different types of passive transport?

Answer 10

Simple diffusion, ion channel, and facilitated diffusion.

Question 11

What is the general function of the nucleus?

Answer 11

• store the main genetic material within the cell
• site of all gene expression

Question 12

Describe the general structure of the nucleus.

Answer 12

• surrounded by a double membrane called the nuclear envelope
• has nuclear pores for mRNA to exit the nucleus
• houses the nucleolus, which contains a very active group of genes that encode and transcribe rRNA

Question 13

What are ribosomes?

Answer 13

Structures made of rRNA molecules and proteins that are the sites of protein synthesis in cells.

Question 14

Are ribosomes considered an organelle?

Answer 14

No because they are not enclosed by a membrane.

Question 15

What is the function of a free ribosome?

Answer 15

To make proteins that are used within the cell.

Question 16

What is the function of a bound ribosome?

Answer 16

To make proteins that are either excreted from the cell, used in the cell membrane, or used in a membrane-bound organelle.

Question 17

Where does protein production take place?

Answer 17

In a netwoek of membrane-bound chambers called the endomembrane system.

Question 18

What are the components of the endomembrane system?

Answer 18

• Smooth ER
• Rough ER
• Golgi apparatus

Question 19

What does the smooth ER do?

Answer 19

Plays a major role in:
- synthesizing lipids
- storing calcium ions
- degrading toxins

Question 20

What does the rough ER do?

Answer 20

• synthesizes proteins that are targeted for export outside the cell

Question 21

What structurally distinguishes the rough ER from the smooth ER?

Answer 21

The rough ER has ribosomes bound to its surface while the smooth ER is smooth.

Question 22

What does the Golgi apparatus do?

Answer 22

• processes proteins
• glycosylation (carbohydrates are added to proteins)

Question 23

What do lysosomes do?

Answer 23

They break down materials in the cell using special hydrolytic enzymes. They can break down old cell parts or destroy invading bacteria.

Question 24

What are the three major components of the cytoskeleton?

Answer 24

Microfilaments, intermediate filaments, and microtubules.

Question 25

Microfilamnets

Answer 25

• smallest
• made of actin protein
• facilitate cell movement

Question 26

Intermediate filaments

Answer 26

• made of fibrous proteins wrapped around one another to form a thick, cable-like structure
• they support cell structures and anchor organelles in the correct positions within a cell.

Question 27

Microtubules

Answer 27

• largest element within the cytoskeleton
• hollow tubes consisting of rows of paired tubulin molecules
• used in cell division, for structural support, and for cell mobility (cilia and flagella)

Question 28

What do mitochondria do?

Answer 28

They convey the energy in food into the form of ATP, which provides energy for many cellular reactions.

Question 29

Describe the basic structure of mitochondria.

Answer 29

• double membrane consisting of a smooth outer membrane and an inner membrane that is contorted into a complex of inter-foldings called cristae.
• the space within the cristae is called the mitochondrial matrix
• the space outside of the cristae but still inside of the outer membrane is the intermembrane space.

Question 30

What form is the genetic material which mitochondria posess?

Answer 30

They possess genetic material in the form of circular DNA.

Question 31

How is mitochondrial genetic material inherited?

Answer 31

Maternally in sexually reproducing organisms.

Question 32

What are chloroplasts?

Answer 32

Double membrane-bound organelles found in plants that are the sites of photosynthesis.

Question 33

What causes the green color of chloroplasts?

Answer 33

Chlorophyll.

Question 34

What form is the genetic material which chloroplasts possess?

Answer 34

They possess genetic material in the form of circular DNA.

Question 35

Explain the endosymbiont theory of eukaryotic evolution.

Answer 35

Mitochondria and chloroplasts have evolved from prokaryotes that inhabited the cells of larger prokaryotes. This was a result of the larger organism engulfing the smaller organism.

Question 36

What evidence do mitochondria present for the endosymbiont theory?

Answer 36

• double membrane
• inner membrane resembles prokaryotic membrane
• circular DNA
• smaller size
• replication similar to binary fission
• able to produce their own protein