Week 1: Different cell types, their structure and function

Question 1

What is a cell?

Answer 1

The fundamental unit of life, capable of carrying out independent processes on its own. Cells are the building blocks of all living organisms.

Question 2

What are the 2 types of cells?

Answer 2

• Eukaryotes - complex and compartmentalised. Found in animals, plants, fungi, algae.
• Prokaryotes - simple structure with no defined nucleus. Found in bacteria and archaea.

Question 3

What are the major common features of both prokaryotic and eukaryotic cells?

Answer 3

• Enveloped by a plasma membrane of similar construction.
• Contain DNA using identical genetic code.
• Use similar transcription and translation processes involving ribosomes of similar structure.

Question 4

What is an organelle, and its function?

Answer 4

Organelles are several specialised compartments within a cell. Each individual organelle carries out specific functions for the cell and they all work together to maintain the life of the cell.

Question 5

What are the major differences between eukaryotic and prokaryotic cells?

Answer 5

• Prokaryotic cells:
  
  • DNA is stored in nucleiods that are not separated from cytoplasm.
  • Very few cytoplasmic organelles.
  • Not all can perform aerobic respiration.
• Eukaryotic cells:
  
  • DNA is housed in a membrane-bound nucleus.
  • Cytoplasm contains complex organelles.
  • Contains mitochondria for aerobic respiration.

Question 6

What are 5 key components below the level of the membrane in a generalised eukaryotic cell?

Answer 6

• Cytoplasm
• Mitochondria
• Golgi complex
• Endoplasmic reticulum with ribosomes
• Nucleus

Question 7

What is cytoplasm?

Answer 7

All the cellular contents between the plasma membrane and the neucleus.

It is comprised of the cytosol (intercellular fluid that surrounds organelles) and various organelles.

Question 8

What is the cytoskeleton?

Answer 8

A network of protein filaments that extend through the cytosol, creating a structural framework for the cell and aids in movement of organelles within the cell.

Question 9

What are ribosomes?

Answer 9

Organelles that are sites of protein synthesis. They contain rRNA (ribosomal RNA), a type of ribonucleic acid.
They are made up of a large and small subunit. These subunits are synthesised separately in the nucleolus (spherical body inside the nucleus) and assemble in the cytoplasm once exiting the nucelolus.

Question 10

What is the endoplasmic reticulum?

Answer 10

The endoplasmic reticulum (ER) is an organelle made up of a network of rough and smooth membranes. It extends from the nuclear envelope (membrane around the nucleus).
* Rough ER extends from the nuclear envelope and folded into a series of flattened sacs. The outer surface is studded with ribosomes. Its purpose is to synthesise glycoproteins and phospholipids.
* Smooth ER extends from the rough ER, it does not have ribosomes attached but does contain unique enzymes. It synthesises fatty acids and steriods.

Question 11

What is the golgi complex?

Answer 11

The golgi complex is an organelle made up of cisternae (small flattened membranous sacs with bulging edges).
It modifes, sorts, packages and transports proteins produced by the rough endoplasmic reticulum. All protiens exported from the cell are processed in the golgi complex.

Question 12

What are mitochondria?

Answer 12

Mitochondria are organelles which generate adenosine triphosphate (ATP), the body’s primary energy source. This is achieved through cellular aerobic respiration.

Mitochondria also play an early role in apoptosis (programmed cell death).

Question 13

Which type of cell contains the highest concentration of mitochondria?

Answer 13

Muscle cells

Question 14

What is the nucelus?

Answer 14

The nucleus is separated from the cytoplasm by the nuclear envelope. Inside the nulceus is the nucleolus The nucleus contains most of a cell’s DNA (deoxyribonucleic acid), controls cellular structure, directs cellular activies, and produces ribosomes via the nucleolus.

Question 15

What are lysomes?

Answer 15

Lysomes are organelles which contain digestive enzymes.
Functions:
* Digest substances that enter the cell via endocytosis.
* Carry out autophagy - digestion of worn out organelles.
* Implement autolysis - digestion of an entire cell.
* Perform extracellular digestion.

Question 16

Name the indicated components of the cell in the picture

Answer 16

Question 17

What is the plasma membrane (cell membrane)?

Answer 17

A flexible structure that envelops every living cell.
Functions:
* Barrier separating inside and outside of the cell.
* Controls the flow of substances into and out of the cell.
* Helps identify the cell to other cells.
* Participates in intercellular signalling.

Question 18

What is main component of the plasma membrane, and what is it made of?

Answer 18

The main component is the lipid bilayer.
This is made of 2 back-to-back layers of 3 different lipid molecules - phospholipids (75%), cholesterol (20%), and glycolipids (5%).

The lipids are amphipathic, with polar hydrophillic heads and non-polar hydrophobic tails.

Question 19

What are the components of the plasma membrane, excepting the phospholipid bilayer?

Answer 19

• Peripheral proteins - attached to polar lipid heads and identify cells.
• Integral (transmembrane) proteins - extend through the lipid bilayer and have varied functions including channels for ions, molecules, and other substances; hormone receptors; carriers; and linkers.
• Cholesterol - prevents fatty acid chains of phospholipid bilayer from packing too closely together.
• Glycolipids - only on the extracellular side of the membrane. perform intercellular interactions.

Question 20

What is membrane fluidity?

Answer 20

Most of the membrane lipids and many of the membrane proteins rotate and move within their own half of the bilayer.

Question 21

What is the selective permeability of the plasma membrane?

Answer 21

The permeability of the plasma membrane varies for different substances.
This is due to the hydrophobic, non-polar interior of the lipid bilayer. This means that the more hydrophobic or lipid-soluble a substance is, the greater the membrane permeability to that substance.
The lipid bilayer is:
* Highly permeable to non-polar molecules (O2, CO2, steriods)
* Moderately permeable to small uncharged polar molecules (water, urea)
* Impermeable to ions and large, uncharged polar moleculees (glucose)

Question 22

How do transmembrane proteins affect the membrane permeability?

Answer 22

Transmembrane proteins act as channels and carriers to increase the plasma membrane’s permeability to a variety of ions and uncharged polar molecules that cannot cross the lipid bilayer unassisted.

Question 23

What is a concentration gradient, in relation to the plasma membrane?

Answer 23

The concentration gradient is the difference in concentration of a chemical from the inside to the outside of the plasma membrane.

Eg. O2 and Na+ ions are more concentrated in extracellular fluid, and CO2 and K+ ions are more concentrated in the cytosol.

Question 24

What is membrane potential?

Answer 24

The difference in electrical charges (electrical gradient) between the inner and outer surface of the plasma membrane.

Question 25

What is an electrochemical gradient?

Answer 25

The combined influence of the concentration gradient and electrical gradient on ion movement.

Question 26

In which direction do substances move due to the concentration gradient?

Answer 26

Substances always move from a more concentrated area to a less concentrated area to reach equilibrium.

Question 27

What are the 2 types of processes that move substances across the cell membrane and what energy is used for these processes?

Answer 27

• Active processes - Cellular energy is used to drive the substance against its electrical/concentration gradient. Usually ATP.
• Passive processes - The substance moves down it’s own electrical/concentration gradient using only its own kinetic energy.

Question 28

How does diffusion affect solutes and solvents?

Answer 28

If a particular solute or solvent is present in a high concentration in one area of the solution, and in low concentration in another area, the molecules will diffuse toward the area of lower concentration until they are evenly distributed within the solution.

Question 29

What is simple diffusion?

Answer 29

Simple diffusion is the passive process in which substances move freely through the lipid bilayer of cells without the help of membrane transport proteins.

Non-polar, hydrophobic molecules use this process. These include fat-soluble vitamins, O2, CO2, nitrogen gasses, fatty acids, steroids.

Question 30

What is facilitated diffusion?

Answer 30

An integral membrane protein (either a carrier or membrane channel) assists a substance across the membrane which is too polar or too highly charged.

Question 31

What are gated membrane channels?

Answer 31

Gated channels are when a portion of the channel protien opens or closes to act as a gate for the passage of ions.

Question 32

What are channel protiens?

Answer 32

Integral membrane proteins that allow specific, small, inorganic ions to pass across the membrane by facilitated diffusion.

Question 33

What is carrier-mediated facilitated diffusion?

Answer 33

A carrier moves a solute down its concentration gradient across the plasma mebrane.

Substances that use carrier-mediated facilitated diffusion include glucose, fructose, galactose, and some vitamins.

Question 34

What is the transport maximum?

Answer 34

The upper limit on the rate at which facilitated diffusion can occur. This is determined by the number of carriers available in a plasma membrane.

Question 35

What is osmosis?

Answer 35

Osmosis is a type of passive diffusion by which there is a net movement of water across plasma membranes from an area of higher water concentration to lower water concentration.

The plasma membrane must be only permanent to water but not to certain solutes.

Question 36

What are the 2 ways water molecules pass through plasma membranes?

Answer 36

• Simple diffusion through the lipid bilayer
• Through aquaporins, integral membrane proteins that function as water channels.

Question 37

What is hydrostatic pressure?

Answer 37

Hydrostatic pressure is the pressure exerted on one side of a membrane which is caused by osmosis creating an increased volume of water on that same side of the membrane.

Question 38

When is equilibrium reached in osmosis?

Answer 38

When the same amount of water molecules move each way across the membrane through osmosis. No further net shift.

Question 39

What is osmotic pressure?

Answer 39

Osmotic pressure is the force exerted by the solution on one side of a semi-permeable membrane that contains a higher concentration of solute. It is the pressure that stops the water molecules from crossing the membrane completely.

Osmotic pressure of a solution is proportional to the concentration of the solute particles on that side of the solution.

Question 40

What is a solution’s tonicity?

Answer 40

A solution’s tonicity is a measure of the solution’s ability to change the volume of cells by altering their water content.

Question 41

What is an isotonic solution?

Answer 41

An isotonic solution is any solution in which the concentration of solutes are the same as those of the intracellular fluid.

Cells in this environment have no change in size or fluid volume.

Question 42

What is a hypotonic solution?

Answer 42

A hypotonic solution is a solution which has a lower concentration of solutes than that of the intracellular fluid.

Cells in this environment absorb fluid and swell.

Question 43

What is a hypertonic solution?

Answer 43

A hypertonic solution is a solution which has a higher concentration of solutes than that of intracellular fluid.

Cells in this environment loose fluid and shrink.

Question 44

What is the active transport process?

Answer 44

Active transport is when energy is required for carrier proteins to move solutes across the membrane against a concentration gradient.

Question 45

What are the 2 types of active transport?

Answer 45

• Primary active transport: powered by energy obtained from hydrolysis of ATP.
• Secondary active transport: powered by energy stored in an ionic concentration gradient.

Question 46

What is vesicular transport?

Answer 46

Vesicles (small, spherical sacs), import materials from and release materials into extracellular fluid. This is an active process that uses ATP.

The 2 types of vesicle transport are:
* Endocytosis: materials move into a cell in a vesicle formed by the plasma membrane.
* Exocytosis: materials move out of a cell by the fusion of vesicles formed inside the cell with the plasma membrane.

Question 47

What are the sizes of the smallest and largest cells in the body?

Answer 47

• Smallest cell: Sperm cell - 4um
• Largest cell: single oocyte - 140um