Introduction to Cells

Question 1

What is a cell?

Answer 1

A cell is a basic unit of life - a cytoplasm surrounded by a phospholipid bilayer.

Question 2

Size of eukaryotic cells, proteins and membranes

Answer 2

Eukaryotic cells - 25μm
Proteins - measured in nm or Angstroms
Plasma membrane - 7nm

Question 3

What is in a cell?

Answer 3

Cells contain organelles, some of which are membrane bound. They also contain molecules such as soluble proteins, ions, nutrients, amino acids, RNA etcetera.

Question 4

What are the differences between prokaryotic and eukaryotic cells?

Answer 4

Prokaryotes are smaller; no membrane bound organelles; DNA found loose in the cytoplasm; haploid; no well defined cytoskeleton.

Question 5

What are plasma membranes made of?

Answer 5

They are composed mainly of phospholipids which is made of a glycerol with two fatty acid tails and a phosphate head.

Question 6

Explain the formation of a phospholipids bilayer in an aqueous environment.

Answer 6

They are amphipathic. In water, they form a bilayer so that the hydrophobic fatty acid tail faces away from water while hydrophilic phosphate head faces water.

Question 7

Explain the permeability of membrane proteins.

Answer 7

The centre is hydrophobic so water soluble substances such as ions can’t pass through but lipd solubles molecules such as cholesterol can. Small molecules also pass through such as water and oxygen.

Question 8

Explain the types and functions of membrane proteins.

Answer 8

Channel proteins - allow charged particles to pass using passive transport through by forming a channel with hydrophilic amino acids in the centre.
Carrier proteins - allows substances to pass through using active and passive transport.
Specific to certain molecules.

Question 9

What is simple diffusion?

Answer 9

A process where a substance travels down a concentration gradient passively through a membrane without proteins channels (e.g. water or oxygen molecules).

Question 10

What is facilitated diffusion?

Answer 10

The transport of a substance down its concentration gradient passively by means of a carrier molecule through a channel protein (e.g. glucose).

Question 11

What is active transport?

Answer 11

The transport of a molecule across a membrane against its concentration using the hydrolysis of ATP at a carrier protein to provide the energy (e.g. sodium-potassium pump).

Question 12

What is the endosymbiont theory?

Answer 12

The theory that mitochondria and plastids, including chloroplasts, originated as prokaryotic cells engulfed by an ancestral eukaryotic cell. The engulfed cell and its host cell then evolved into a single organism.

Question 13

What is cancer?

Answer 13

It is an uncontrolled cell growth leading to increasing disorganisation of tissues.

Question 14

Define metastasis.

Answer 14

The development of a secondary malignant tumour at a distance from the primary site of cancer.

Question 15

What is a necrotic tumour?

Answer 15

It is the late stage when the cells start to die due to lack of blood supply.

Question 16

What are the mutations which lead to cancer?

Answer 16

1. The divide/don’t divide signal is broken.
2. No limit on cell division.
3. Loss of correction mechanism during DNA copying.
4. Ability to evade the immune system.
5. Ability to recruit blood vessels for the tumour.
6. Ability to migrate into blood stream.

Question 17

What are the main functions of blood?

Answer 17

Transport; heat distribution; immunity; haemostasis; support; maintaining homeostasis.

Question 18

What are the major components of blood?

Answer 18

Blood is made up of erythrocytes, leukocytes and plasma containing various proteins and ions.

Question 19

What are the properties of erythrocytes?

Answer 19

No nucleus or most organelles; mostly filled with haemoglobin to transport oxygen; biconcave shape for flexibility and maximum surface area.

Question 20

What are the properties of haemoglobin?

Answer 20

Quaternary protein made of 2 alpha globin and 2 beta globin chains; haem group in the middle containing iron; binds to and carries oxygen; carries CO2 by breaking it down with carbonic anhydrase.

Question 21

What is anaemia?

Answer 21

Anaemia is the deficiency in the concentration of haemoglobin in erythrocytes. There are three types: microcytic, normocytic and macrocytic.

Question 22

How are erythrocytes produced?

Answer 22

They are produced in the bone marrow when the erythropoietin hormone increases. The process is erythropoiesis.

Question 23

What is a haematocrit?

Answer 23

It is the ratio of the volume of erythrocytes to the total volume of blood.
Normal range check.

Question 24

What is MCV?

Answer 24

MCV = Mean cell volume.

It is the average volume of the erythrocytes.

Question 25

What is microcytic anaemia? What causes it?

Answer 25

A lower than average MCV. It is caused by iron deficiency due to menstruation, GIT lesions or cancers.

Question 26

What is normocytic anaemia? What causes it?

Answer 26

A normal MCV. It is due to blood loss.

Question 27

What is macrocytic anaemia? What causes it?

Answer 27

A larger than average MCV. It can be due to Vitamin B12 deficiency (pernicious anaemia) or folic acid deficiency (usually during pregnancy).

Question 28

Why were Hammerhead Fruit Bats unaffected by Ebola?

Answer 28

Ebola virus entry requires a cholesterol transporter called Niemann-Pick C1. An Npc1 mutation in these bats leads to low grade infection and carrier status.

Question 29

What are the main types of infectious agents for humans?

Answer 29

Viruses, bacteria, fungi, protozoa and helminth parasites.

Question 30

What are the distinguishing features of viruses?

Answer 30

Not cells in their own right (obligate parasites); use host machinery to replicate; show host specificity but infect all life forms; divide by budding.

Question 31

Give an example of a virus and the disease it causes.

Answer 31

Human Immunodeficiency Virus (HIV) is a retrovirus that causes Acquired Immune Deficiency Syndrome (AIDS); transmission through blood due to open wounds or cuts.

Question 32

What are distinguishing features of bacteria?

Answer 32

Prokaryotes (contain DNA in condensations called nucleoids); some are pathogenic; divide by binary fission.

Question 33

Give examples of bacteria and the diseases they cause.

Answer 33

Shigella is a family of bacteria that causes an intestinal infection called shigellosis; faecal-oral transmission.
Neisseria Meningitidis (Meningococcus) causes meningitis as well meningococcemia (a life threatening sepsis); spread by close or lengthy contact (not very contagious).

Question 34

What are the distinguishing features of fungi?

Answer 34

Eukaryotic; occurs as yeast, buds or both; divide in several ways including budding.

Question 35

Give an example of a fungi and the disease it causes.

Answer 35

Candida albicans is a fungi that causes thrush in the mouth and mycoses on the skin; it also causes Invasive Candidiasis when it enters the blood leading to candidemia (a bloodstream infection); part of normal human flora and only a problem if excessive in numbers.

Question 36

What are the distinguishing features of protozoa?

Answer 36

Unicellular eukaryotic organisms; complicated life cycle with two hosts; replicate in host by binary fission.

Question 37

Give an example of a protozoa and the disease it causes.

Answer 37

A genus called Plasmodium causes malaria; spread by mosquitoes (the vector).

Question 38

What are distinguishing features of Helminth parasites?

Answer 38

Multicellular eukaryotes; visible to naked eye; life cycles ranging from simple embryonation to alternation of generation.

Question 39

Give an example of a Helminth parasite and the disease it causes.

Answer 39

Roundworms (Ascaris) causes intestinal infection called Ascariasis; faecal-oral transmission.