Lecture VI/VII: The Cell

Question 1

Why are cells so small?

Answer 1

It has to do with the fact that larger objects have a smaller surface area to volume ratio than smaller objects.
Cells must be big enough to fit all the necessary molecules/organelles, but small enough so that the surface area of the cell is sufficient to support the metabolic activities happening inside the cell.

Question 2

What is an example of an adaptation to increase the cell surface to volume ratio?

Answer 2

Cells making up the lining of our small intestines have small extensions on their plasma membranes called microvilli. This increases the cell surface area aiding in their primary function of absorption of digested nutrients.

Question 3

What are the characteristics of Procakyrotic Cells?

Answer 3

Small in size 1 -10 µm

DNA in a circular loop and not enclosed within it’s own membrane, but found in the Nucleoid region of the cytoplasm.

Lack organelles

Ribosomes present

Cytoplasm fills the cell.

Cell wall present exterior to the plasma membrane.

Question 4

What are the characteristics of eukaryotic cells?

Answer 4

Larger in size 10 -100 µm

DNA in linear strands and enclosed within it’s own membrane = nucleus

Contain many membrane bound organelles each with specialized functions.

Cytoplasm fills most of the cell, but is not found within the nucleus.

Ribosomes present

Question 5

What is an Organelle?

Answer 5

A phospholipid membrane bound (enclosed) structure that has a lumen (space) where a specialized function is performed for the cell.

Question 6

What is the difference between Plant and Animal cells? What are the components that are unique to Plant cells?

Answer 6

Plants and animals are structurally very different and acquire their energy and nutrients in significantly different ways.  Certain cellular characteristics have evolved in each group that are not found in the other.
Chloroplasts
Central vacuole
Cell wall
Plasmodesmata

Question 7

What is the plasma Membrane? What are the two main components?

Answer 7

A semi-permeable membrane separating the intracellular environment from the extracellular environment.
Aids in homeostasis by controlling the passage of substances into and out of the cell.
made of Proteins and Phospholipids.

Question 8

What do proteins do in the plasma membrane?

Answer 8

Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachement to the cytoskeleton and extracellular matrix.

Question 9

What is the Nucleus?

Answer 9

Large organelle housing the DNA of the cell (chromatin) enclosed by a double membrane called the nuclear envelope.
The nuclear envelope is studded with nuclear pores for exchange of substances between the nucleus and cytoplasm of the cell.

Question 10

What is the Nucleolus?

Answer 10

The nucleolus is the darker region within the nucleus. It’s function is to make ribosomes. It is not considered an organelle (not enclosed by a membrane).

Question 11

What is the Mitochondria and its roles?

Answer 11

Found in eukaryotic cells, (plants too)
powerhouse of the cell.
Double membrane (smoother outer and convoluted inner membrane)
have their own DNA and ribosomes???
Function: Cellular respiration, they harvest bond energy from glucose and other metabolites and use it to make adenosine triphosphate (ATP) the cellular energy molecule.

Question 12

What are chloroplasts and their roles?

Answer 12

In plant cells and some protist cells only
Double membrane and have their won DNA and ribosome as well?
Contain chlorophyll within the internal structure called thylakoids
function: photosynthesis: transform light energy into bond energy forming glucose molecules.

Question 13

Why do mitochondria and chloroplasts, have their own DNA and ribosomes?

Answer 13

If you remove the itochondriorn or the chloroplast from an eukaryotic cell you would see that they would have many simialrieties with prokaryotic cells inclusding a circular DNA moleculae and thei own ribosomes.
This leads to Endosymbiont Theory

Question 14

What is Endosymbiont Theory

Answer 14

This theory states that an early ancestor of eukaryotic cells engulfed a bacterial cell by phagocytosis. But instead of the bacterium being digested it remained intact within the eukaryotic cell.

There is evidence supporting that this occurred 2 times independently. Once with a bacteria that could perform aerobic cellular respiration (became eukaryotic mitochondria) and then at another time with a bacteria that could perform photosynthesis (became eukaryotic chloroplasts). Over the course of time these bacteria lost their ability to live independently from the eukaryotic cell and became the organelles that we are familiar with.
These additions of prokaryotic DNA, contained within mitochondria and chloroplasts, are considered 2 distinct horizontal gene transfer events in the evolutionary history of living organisms.

Question 15

What is the particularity of the reproduction of mitochondrial DNA?

Answer 15

Only the Mitochondrion DNA is taken from the mother.

Question 16

What is peroxisomes and their role?

Answer 16

Contain enzymes that with the help of oxygen:

Breakdown fatty acids to be used as fuel for cellular respiration.

Breakdown cellular toxins.

Question 17

What is the cytoskeleton and its role? What are the 3 types of protein fibers?

Answer 17

The cytoskeleton is a network of protein fibers that help organize structures within the cell as well as help with movement.
3 different types of protein fibers:

Microtubules, Intermediate filaments, and Microfilaments make up cytoskeleton components in varying quantities.

Scaffolding that supports all organelles within the cell and aids in movement of substances inside the cell.

Make up the Centrosome and spindle fibers involved in cell division.

Cilia and Flagella; specialized cytoskeleton structures which are located on the exterior surface of cells that aid in movement.

Question 18

Movement within cells?

Answer 18

Protein fibers move organelles and vesicles from one place to another within the cell.
(view picture)

Question 19

Movement of cells?

Answer 19

Some cells can move through their environment by cytoplasmic streaming (movement of cytoplasmic contents via cytoskeleton filaments) creating pseudopods that pull them along.

Question 20

What is the Centrosome and its role?

Answer 20

The anchor point for the cytoskeleton.

Made up of a pair of centrioles (concentrations of microtubules).

Help direct the movement of chromosomes during cell division.

Question 21

Movement exterior to the cell? Functions?

Answer 21

Extensions of the cytoskeleton outside of the cell’s surface.

Flagella:
Longer and whip like

Cilia:
Short and thin protrusions of the cytoskeleton.

Functions:
Motility of the cell.
Motility of substances along tissue surfaces.

Question 22

Movement on tissue surfaces? (example)

Answer 22

Movement of the cilia removes mucus and inhaled foreign debris out of our respiratory tract.

Question 23

Extracellular Components and Connections between Cells?

Answer 23

Exterior to the plasma membrane of cells you will find extracellular components that help the cell maintain its shape and provide a method of connecting and communicating with adjacent cells in tissues.

Plant cell walls
Extracellular matrix of animal cells
Cell Junctions
Plasmodesmata (plant cells)
Tight junctions (animal)
Desmosomes (animal)
Gap junctions (animal)

Question 24

Role of Plant cell walls? Made of?

Answer 24

Protect the cell.

Allow plants to grow tall by providing structural support.

Made primarily of cellulose.

Question 25

Extracellular Matrix? What is it? Role? made of?

Answer 25

Animal cells lack a cell wall, but they have an extracellular matrix (ECM) that lends support to the cell.

Made up of fluid or substances as dense as calcium phosphate (bone matrix). Often contains protein fibers of varying thickness (e.g. Collagen) and carbohydrates.

Question 26

Cell Junctions? Example

Answer 26

Cells come together to form different types of tissues within plants (leaves, stems, roots) and animals (muscle, connective, nerve etc….).

These cells need to be connected to support the structure of the tissue and also to allow rapid communication between cells.
Example: Plasmodesmata (plants only): Create channels between cells. Cytoplasm can travel from one cell to another. Passage of nutrients, water and chemical messengers.

Question 27

Animal Cell Junctions? what are the three of them?

Answer 27

Tight Junctions:
Form a tight seal between cells so that there is no leakage from within an organ. E.g. Contents of stomach, blood vessels, urinary bladder etc…

Desmosomes:
Anchor cells together giving strength to tissues. E.g. Hold muscle cells together during contraction.

Gap Junctions:
Like plasmodesmata. Communication channels between animal cells. Allow flow of cytoplasm including water, nutrients and chemical messengers.

Question 28

What are the cell components in eukaryotic cells inside the cytoplasm?

Answer 28

Ribosomes

The Endomembrane System 
  Endoplasmic Reticulum (Rough and 
  Smooth)
  Golgi Apparatus
  Lysosomes 
  Vacuoles

Question 29

Cytoplasm?

Answer 29

The cytoplasm includes the fluid (Cytosol) and all of the organelles that exist outside of the nucleus that are enclosed by the plasma membrane.

Question 30

Ribosomes? Function?

Answer 30

Ribosomes are molecular complexes made up of 2 subunits (look like cream puffs!).

Ribosome subunits are composed of protein and ribosomal RNA (rRNA).

Ribosomes are made in the nucleolus in the nucleus, but proteins are made in the cytoplasm. Each ribosome must make it’s way into the cytoplasm via a nuclear pore.

The function of ribosomes is to aid in the translation of mRNA genetic code into protein amino acid sequence during protein synthesis.

Ribosomes embedded in the rough ER generally make proteins destined to be inserted within the plasma membrane of the cell or to be exported from the cell, for example protein hormones.

Question 31

What are the fucntions of the endomembrane system?

Answer 31

Regulates protein and lipid traffic in the cell.

Performs metabolic functions

Question 32

Transportation within the endomembrane system?

Answer 32

Phospholipid membranes can pinch off from one organelle forming a vesicle and then fuse with another for the transportation of materials from one organelle to another or for release of cell products outside of the cell.

Question 33

Rough Endoplasmic Reticulum (rER)? functions?

Answer 33

Surrounds the nucleus.

Highly folded membranous organelle. Called rough because it’s surface is studded with ribosomes.

Functions:
Makes and processes proteins that will be exported out of the cell.

Makes plasma membrane components (phospholipids and proteins).

Question 34

Smooth Endoplasmic Reticulum (sER)? Functions?

Answer 34

Continues out from the rough ER. It is not studded with ribosomes.

Main Functions:
Synthesize lipids

Detoxification of drugs and poisons

Storage of calcium ions

Question 35

What do the transport vesicles do?

Answer 35

The will transport the vesicles that carry proteins or lipids from the rough or smooth endoplasmic reticulum to the golgi apparatus.

Question 36

What is the golgi apparatus and the role?

Answer 36

Highly folded membranous organelle. Receives proteins and lipids from the ER via transport vesicles.

Main Function:

Modifies and stores proteins and lipids until needed. Sends them out in transport vesicles to be used by the cell or to be exported from the cell.

Question 37

Lysosomes? roles?

Answer 37

Organelles containing digestive enzymes (Hydrolases) for breaking down macromolecules and damaged organelles within cells.

Lysosomes are involved in 2 processes:
Autophagy
Phagocytosis

Question 38

What is autophagy

Answer 38

Destruction of dysfunctional cell components and cell debris. Molecular components released from the process can be reused by the cell to make new structures.

Question 39

What is Phagocytosis?

Answer 39

Cell engulfs a food particle or parasitic cell (in the case of white blood cells in our bodies) forming a vesicle/vacoule.

Vesicle fuses with a lysosome and is digested within the cell.

Question 40

Different types of vacuoles?

Answer 40

Food Vacuoles:
Formed by phagocytosis

Contractile Vacuoles:
Highly specialized to pump out excess water from certain unicellular eukaryotic organisms, e.g. paramecium.

Central Vacuoles:
A common feature of mature plant cells. Holds water and ions. Aids in plant growth by increasing cell size.

Other Plant Vacuoles:
Storage of protein, poisons, or pigments

Question 41

Summary of the Endomembrane System

Answer 41

The nuclear envelope is connected to the rough ER which is continuous with the smooth ER.

Proteins and plasma membrane components produced by the ER travel to the Golgi apparatus in transport vesicles.

In the Golgi apparatus they are processed and stored. Upon demand, products are repackaged into transport vesicles.

Transport vesicles containing digestive enzymes remain in the cytosol and function as lysosomes while others travel to the plasma membrane where contents (proteins or lipids) will be incorporated into the plasma membrane or exported from the cell.