Introduction: the cell (Dr. Boucrot)

Question 1

What is a cell ?

Answer 1

In biology, the cell is the basic unit of life.

Question 2

What is an organism ?

Answer 2

An organism is a collection of specialized cells.

Question 3

How many cells does the human body contain ?

Answer 3

Between 70 and 100 trillion cells (1 trillion = 10E12).

Question 4

How many new cells are made every day in the human body ?

Answer 4

Around 300 billion.

Question 5

What are the main differences between prokaryotic and eukaryotic cells ?

Answer 5

Prokaryotic cells have a 1-2 micron diameter, no nucleus, circular DNA (so one chromosome), divide by binary fission, rarely possess internal membranes, have 70S (50S+30S) ribosomes, no cytoskeleton, move via a rotary motor that drives bacterial flagellum, first appeared 3.5 billion years ago.
Eukaryotic cells have a 5-100 microns diameter, have a nuclear, linear DNA with multiple chromosomes and proteins, go through mitosis (to produce daughter cells) and meiosis (to produce gametes), possess lots of internal membranes (organelles), have 80s (60s+40S) ribosomes), cytoskeleton made of microtobules, move via dynein (that drives eukaryotic flagellum cilia), kinesin and myosin, first appeared 1.5 billion years ago.

Question 6

What do we call the classification of organisms ?

Answer 6

Taxonomie.

Question 7

What are the distinct growth and division stages of cells ?

Answer 7

G1 (RNA and protein synthesis), S (DNA replication), G2 (RNA and protein synthesis), M (cell division or mitosis) and cytokinesis (cytoplasm of mother cell split in two, giving two daughter cells. G1+S+G2 = interphase.
There is also G0, a resting state where the cell is actively preparing to divide and just performing its function (post-mitotic) e.g. neurons, certain liver cells storing carbohydrates.

Question 8

What is mitosis ?

Answer 8

Mitosis is the cell division that produces two daughter cells form one mother cell, each daughter cell have the same number and kind of chromosomes as the mother cell. It occurs in four stages: prophase, metaphase, anaphase, telophase (and usually finishes with cytokinesis).

Question 9

What is meiosis ?

Answer 9

Meiosis is a cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.

Question 10

How many chromosomes does the human genome contain ?

Answer 10

23 pairs of chromosomes (46 total).

Question 11

How many basepairs does the human genome contain ?

Answer 11

Around 3.10E9 unique basepairs.

Question 12

What is ploidy ?

Answer 12

Ploidy is the number of sets of chromosomes in a cell. (n=haploid, 2n=diploid, 3n=triploid, 4n=tetraploid…)

Question 13

What is euploidy ?

Answer 13

Euploidy is having an integral set of chromosomes.

Question 14

What is aneuploidy ?

Answer 14

Aneuploidy is not having ploidy (an integral set of chromosomes).

Question 15

What does polarity mean in cells ?

Answer 15

Polarity in cells can mean a difference in electrical charge between two sides of the cell but it can also mean that one side of the cell is functionally different from the other.

Question 16

How are differentiated cells produced and what are the parent cells called ?

Answer 16

Differentiated cells are produced by asymmetric division and the parent cells are called “stem cells”.

Question 17

What is the ultimate stem cell (a totipotent stem cell) ?

Answer 17

The fertilized egg is the ultimate stem cell, capable of producing a human containing about 10E14 cells.

Question 18

What is cellular differentiation ?

Answer 18

Cellular differentiation is the changing of a cell as it acquires new properties as a result of an extracellular signal. Differentiated cells show different patterns of gene expression.

Question 19

From what stem cells do red blood cells (erythrocytes) develop from ?

Answer 19

Erythrocytes develop from multipotent hematopoietic stem cells in the bone marrow. These also give rise to granulocytes (phagocytic immune cells), monocytes (macrophage precursors), eosinophils (cells active in allergic regions, fighting parasites), megakaryocytes (latest-forming cells, and T and B cells of the immune system.

Question 20

What is an organelle ?

Answer 20

An organelle is any of a number of organized or specialized structures within a living cell.

Question 21

What is the plasma membrane’s function ?

Answer 21

The plasma membrane controls the movement of molecules in and out the cell, cell adhesion and cell signaling.

Question 22

What is the mitochondria’s function ?

Answer 22

The mitochondria is the “power plant” of the cell: it has it’s own double membrane and genome, it is the principal site of ATP synthesis (where the citric acid cycle takes place).

Question 23

What is the lysosome’s function ?

Answer 23

Lysosomes are acidic and contain enzymes that degrade obsolete cellular components.

Question 24

What is the nuclear envelope ?

Answer 24

The nuclear envelope, nucleolemma or karyotheca, is the phospho lipid bilayer which surrounds the genetic material and nucleolus in eukaryotic cells. The nuclear membrane consists of two lipid bilayers—the inner nuclear membrane, and the outer nuclear membrane.

Question 25

What is the nucleolus ?

Answer 25

The nucleolus is a small dense spherical structure in the nucleus of a cell during interphase.

Question 26

What is the nucleus ?

Answer 26

The nucleas is a double-membrane bound organelle containing most of the cell’s genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The synthesis of mRNA and tRNA occurs in the nucleus.

Question 27

What is the Smooth Endoplasmic Reticulum or SERs function ?

Answer 27

The SER is responsible for the synthesis of fatty acids and phosphilipids, and the storage of calcium ions.

Question 28

What is the Rough Endoplasmic Reticulum of RER’s function ?

Answer 28

The RER (rough because of the ribosomes on it) is the site of protein synthesis, protein glycolysation and protein folding.

Question 29

What is the Golgi complex’s function ?

Answer 29

The golgi complex is responsible for protein sorting, protein modification and protein transport in vesicles.

Question 30

What are the functions of the secretory vesicles ?

Answer 30

Secretory vesicles store proteins and small molecules until they are signaled to release them as part of the regulated secretory pathway (e.g. vesicles in synaptic terminals of neurons). While some fuse with the cell’s plasma membrane, others do not.

Question 31

What is the peroxisome’s function ?

Answer 31

The peroxisome convert hydrogen peroxide (H2O2) into water (H2O).

Question 32

What are the roles of cytoskeletal fibers ?

Answer 32

Cytoskeletal fibers form networks via microtubules, microfilaments and intermediary filaments. They support membrane, organize organelles and are important for cell cell movement.

Question 33

What is the plasma membrane’s composition ?

Answer 33

The plasma membrane is made of a phospholipid bilayer with hydrophobic fatty acyl side chains faced towards each other and hydrophilic phospholipid head groups facing the aqueous cytosol and ectoplasm. The membrane contains a vast array of associated proteins (pumps, carriers, channels…).

Question 34

What are the major lipid component of biological membrane ?

Answer 34

The major lipid components of biomembranes are phosphatidylethanolamine + phosphatidylserine (PE+PS), situated on the cytosolic side, phosphatidylcholine (PC), situated on the exoplasmic side, sphingomyelin (SM) situated on the exoplasmic side, and cholesterol situated on both.

Question 35

What properties does cholesterol give tophosphatidylcholine (PC) ?

Answer 35

Cholesterol can bind to PC molecules and allow them to elongated by 0.5nm.

Question 36

What properties can phosphatidylethanolamine (PE) confer to the lipid bilayer ?

Answer 36

Phosphatidylethanolamine (PE) regulates membrane curvature.

Question 37

To what is the phospholipid bilayer permeable ?

Answer 37

The membrane bilayer is permeable to small gases (CO2, N2, O2), small unchared polar molecule (ethanol), it is slightly permeable to water and urea. It is unpeermeable to large uncharged polar molecules (glucose, fructose), ions (K+, Cl-, Mg2+) and charged polar molecules (amino acids, ATP, proteins, nucleic acids)

Question 38

Cellular functions require energy. Where does this energy come from ?

Answer 38

This energy comes from the hydrolysis of ATP to ADP or AMP. ATP possess two “high energy” phosphoanhydride bonds (link between phosphorous atom of one phosphate group and the oxygen atom of another phosphate group) between the alpha and beta phosphate and between the beta and gamma phosphate. The braking of these bonds releases a large amount of energy.

Question 39

How do the properties of the phospholipid bilayer vary with temperature ?

Answer 39

At physiological temperate, the membrane bilayer has a gel-like consistency. When we add heat to the system, it acquires a fluid like consistency.

Question 40

What is a monomer ?

Answer 40

A monomer is a molecule that can be bonded to other identical molecules to form a polymer.