fundamentals of cell biology and cell=cell interactions

Question 1

Where is the Cytoplasm and Cytosol found?

Answer 1

found between the cell membrane and nucleus

Question 2

Describe cytoplasm and cytosol

Answer 2

It is a thick, jelly-like substance in which cellular organelles are suspended.
The liquid portion or matric of the cytoplasm is called cytosol.
This intracellular fluid contains a number of dissolved materials which have nutritive value.
Cytosol is a very thick fluid in which diverse cell structures are suspended.

Question 3

The Nucleus

Answer 3

The nucleus is a membrane-bound organelle that contains the genetic material (DNA) of eukaryotic organisms.

Question 4

Besides housing DNA, therefore making it the command centre of the cell, it also:

Answer 4

Copies DNA and passes it onto daughter cells during cell division.
Produces rRNA and proteins.

Question 5

Structure of the nucleus:

Answer 5

It is enclosed with a double membrane.
This nuclear envelope is punctured randomly forming nuclear pores. These pores make the nucleus more permeable than the cell membrane, i.e. allowing large molecules to pass through it.
Within the nuclear membrane is a jelly-like liquid called nucleoplasm (similar to cytoplasm).
Nucleolus (plural = nucleoli) is the largest structure in the nucleus. It is the site where ribosomal RNA (rRNA) is made. Nucleoli are made up of proteins, DNA and RNA.
DNA is arranged into thread-like strands known as chromatin which can condense or concentrate into rod-like structures known as chromosomes.

Question 6

Ribosomes

Answer 6

These are macromolecular machines that function to synthesise proteins according to the instructions from the nucleus.

Ribosomes are complexes made up of ribosomal ribonucleic acid (rRNA) and proteins.

Ribosomes use instructions sent from the nucleus to carry out protein synthesis.

Question 7

Ribosomes are found at two locations within the cytoplasm

Answer 7

Location 1 – Ribosomes are suspended in the fluid of the cytoplasm (free ribosomes).
Location 2 – Ribosomes attached to the outside of the ER or nuclear envelope (bound ribosomes).
Free and bound ribosomes are structurally identical and can change positions at any time.
Free and bound ribosomes have the same function of protein synthesis.
Free ribosomes generally manufacture proteins that are used within the cell.
Bound ribosomes generally manufacture proteins that are transported out of the cell to be used elsewhere.

Question 8

Endoplasmic Reticulum

Answer 8

The endoplasmic reticulum (ER) is an extensive network of membranes that serves multiple functions.

The ER consists of a network of membranous tubules and sacs called cisternae.

The ER membrane separates the internal compartment of the ER called the ER lumen (cavity) from the cytoplasm.

This large organelle is continuous with the nuclear envelope.

Question 9

There are two distinct regions of the ER:

Answer 9

Smooth ER: The outer surface lacks ribosomes.
Rough ER: The outer surface has ribosomes.

Question 10

Some functions of the Smooth ER

Answer 10

Lipid synthesis, e.g. phospholipids.
Detoxification of drugs and poisons.
Steroid production, e.g. steroids secreted by the adrenal gland.
Sex hormone production, e.g. progesterone, testosterone.
Storage of calcium ions in muscle cells.

Question 11

Some functions of the Rough ER:

Answer 11

Rough ER is covered with ribosomes which are the site for protein synthesis.
It is also responsible for transporting these newly made proteins in vesicles to the Golgi apparatus.
Rough ER also makes its own membrane phospholipids.

Question 12

Golgi Apparatus

Answer 12

Also known as the Golgi body or Golgi complex is a series of flattened sacs = cisternae, that are stacked one on top of another.
The GA is located in the cytoplasm as part of a group of membranes and organelles in eukaryotic cells that works together to modify, package and transport lipids and proteins called the endomembrane system.

Question 13

The two poles of the Golgi stack are referred to as cis face and trans face:

Answer 13

Cis face is the receiving side of the GA. It is situated near the ER. The transport vesicles that formed from the ER, travel to the cis face, fuse with it and empty their contents into the lumen of the GA.
Trans face is situated at the opposite end of the cis face. Here, the GA gives rise to vesicles which pinch off and travel to other sites carrying newly formed proteins.
Proteins are usually modified during their transit from the cis face to the trans face of the GA.

Question 14

Some major functions of the GA include:

Answer 14

Modifying, sorting and packaging proteins and lipids for secretion.
Transporting lipids around the cell.
Synthesising lysosomes.
Manufacturing certain macromolecules such as polysaccharides, e.g. pectin.

Question 15

Mitochondrion

Answer 15

Mitochondria (plural for mitochondrion) are membrane-bound cell organelles that generate most of the chemical energy needed to power the cell’s metabolic reactions.

Mitochondria are unique in that they have their own DNA that allows them to replicate themselves (called mitochondrial DNA). They are, therefore, considered semiautonomous.

Question 16

Structure of the mitochondrion:

Answer 16

Mitochondria are elongated organelles, encased by a double membrane.
The external membrane is smooth and gives the mitochondrion its shape. It controls the entrance and exit of substances into and out of the mitochondrion.
The internal membrane is highly folded into structures called cristae. These folds increase the surface area which increases productivity.
The space between the internal and external membrane is called the inter-membrane space. Ions are stored here.
The inside of the mitochondrion is called the matrix. Enzymes for energy production and molecules such as ribosomes and mitochondrial DNA can be found here.

Question 17

Function of mitochondria:

Answer 17

Mitochondria are the powerhouses of the cell.
Mitochondria take in nutrients, digest them and then create energy-rich molecules called adenosine triphosphate (ATP) which are used by all cells for energy.
Cellular respiration is the process of breaking down sugar for energy production.
Most of the reactions needed to generate ATP occur in the internal membrane.