Lecture 3

Question 1

What is the function of the nucleus?

Answer 1

Largest organelle of eukaryotic cells.
Absent in red blood cells
* Houses the nuclear DNA, with the
instructions for protein synthesis
* Controls all the cellular activities.
▪ the “brain” of the cell.
* Site of DNA replication and the synthesis of
different RNAs (rRNA, mRNA, tRNAs etc)

Question 2

What is the structure of the nucleus?

Answer 2

Nuclear envelope(s): he nucleus double membrane, composed of:
▪ outer nuclear membrane - continuous with the
endoplasmic reticulum

• Both membranes fuse at nuclear pores
  ▪ ringlike channels made by proteins that regulate the
  exchange of molecules in/out the nucleus
  ▪ allowing selective molecules transport

Question 3

What are three structures inside the nuclear envelope?

Answer 3

Nucleoplasm, Nuclear lamina, Nucleolus

Question 4

Structure of Nucleoplasm?

Answer 4

Nucleoplasm the viscous fluid within the nucleus
▪ Includes different molecules including the nuclear DNA

Question 5

Structure of Nuclear Lamina?

Answer 5

a network of intermediate filaments
that is associated to membrane proteins of the inner
nucleus envelope that extend within the nucleus
▪ It provides mechanical support
▪ It regulates DNA replication and cell division

Question 6

Structure of Nucleolus?

Answer 6

Nucleolus is a distinct sub-region of the nucleus, not surrounded by a membrane
▪ the site of ribosomal RNA (rRNA) synthesis
▪ rRNA assembly with ribosomal proteins into ribosome subunits

Question 7

What’s the genome arrangement In the nucleus like?

Answer 7

Nuclear DNA
▪ Multiple linear DNAs (chromosomes) that
are condensed and wrapped around
histones to form chromatin → lec. 3
▪ In mitosis (lec. 8), chromatin is further
condensed into X-shaped chromosomes
▪ DNA is in the nucleoplasm (outside nucleolus)

Question 8

What is the endomembrane system?

Answer 8

Nucleus is connected to a group of interconnected organelles by a system of
continuous membranes and vesicles → Endomembrane system
▪ System where organelles work together for synthesis, modification, and transport of
proteins & lipids – a secretory pathway for proteins (insulin, antibodies) secreted outside

Question 9

What is the Endoplasmic reticulum?

Answer 9

ER is a network of tubes and flattened sacs
(made of membranes) called cisternae running
throughout the cytoplasm

Question 10

What two functional components make up the ER?

Answer 10

Two functional components:
➢ rough ER
▪ with associated ribosomes
➢ smooth ER
▪ without ribosomes

Question 11

What are the functions of the smooth end reticulum?

Answer 11

Functions:
➢Lipid synthesis (fatty acids, phospholipids, steroid hormones)
➢Calcium storage (which regulates many cell activities)
▪ E.g.: muscle contraction & cell signalling pathways (Lec. 7)
➢Detoxification of drugs and alcohol (in liver cells) → drug metabolism

Question 12

What are the functions of the Rough ends reticulum?

Answer 12

Functions:
➢ Protein synthesis (due to ribosomes on the ER)
➢ Protein modifications & folding
▪ glycosylation (addition of carbohydrates),
▪ Oligomerisation (assembly of multiple protein subunits)
▪ Disulphide bond formation (structural stabilisation)
➢ Protein sorting/trafficking (signal sequence)

Question 13

What are transport vesicles?

Answer 13

Enclosed membranous compartments (tiny sacs) to
transport molecules (proteins, lipids) between organelles

Question 14

How do transport vesicles work?

Answer 14

The lipid bilayer nature of membranes allows transport
vesicles to bud off from organelles and fuse with
lipidic target membranes

Question 15

What are the cell transport mechanism for proteins and other molecules?

Answer 15

from rough ER to Golgi
➢ from Golgi to the cell membrane
➢ from Golgi to lysosomes

Question 16

What is the Golgi body?

Answer 16

Stacks of flattened, membranous sacs (cisternae)

Question 17

What is the function of the Golgi body?

Answer 17

Protein modification into mature/stable proteins
▪ Glycosylation (addition/removal of carbohydrates)
▪ Phosphorylation (addition of phosphate groups)
▪ Proteolysis (Protein cleavage for activation)
* Lipid modification
* Protein/Lipid sorting to their final destination:
➢ Lysosome
➢ Plasma membrane by secretory vesicles (exocytosis- Lec.7)
➢ Outside the cell via exocytosis (e.g. hormones)

Question 18

What is the structure of a lysosome?

Answer 18

Lipid membrane – protecting the cytosol from its digestive enzymes (protection)

Internal lumen – Includes many different acid hydrolyses ( ̃50-60 types):E.g. Proteases → proteins and peptides, Lipases → lipids, Nucleases → nucleic acids,Internal acidic pH of 4–5 is maintained for enzymatic activity efficacy
➢ Acid enzymes have no activity at neutral pH of the cytosol (protection in case of leaking)

Question 19

What are the functions of lysosomes?

Answer 19

Main digestive system of the cell (“cell’s waste bin”):
➢ Degrade and recycle damaged organelles (autophagy)
➢ break down cellular macromolecules & recycle monomers
➢ Digest bacteria → phagocytosis in some immune cells

Question 20

What are peroxisomes?

Answer 20

Oxidative organelles contain:
➢ Lipid membrane → compartmentalisation
➢ Core with oxidative enzymes (eg catalase, urate oxidase)

Question 21

What are the functions of peroxisomes?

Answer 21

Oxidation reactions to break down long fatty acid chains and amino acids,
▪ Sometimes, generating hydrogen peroxide (H2O2), highly toxic
* The enzyme catalase neutralises harmful substances (eg alcohol, formaldehyde)
▪ Catalase uses H2O2 to oxidise substrates, neutralising it to H2O + O2

Question 22

Where are mitochondria and how does this differ?

Answer 22

Present in all eukaryotic cells (Absent in red blood cells)
▪ Numbers increase in cells with high energy demand

Question 23

What are the functions of mitochondria?

Answer 23

ENERGY GENERATION/CONVERSION
▪ Site of metabolic reactions (cellular respiration)
that in aerobic conditions (with O2), convert
chemical energy from organic molecules into
energy usable by the cells (ATP)
Induction of programmed death cell (apoptosis) – Lec. 9
* Heat production (in brown adipose tissue)
* Calcium homeostasis

Question 24

What four parts make up the mitochondrial structure?

Answer 24

➢ The outer membrane
➢ The intermembrane space
➢ The inner membrane folded into cristae
➢ The matrix

Question 25

Describe the structure and features of the outer membrane

Answer 25

simple lipid membrane. High permeability
▪ It contains proteins (porins), which allow
molecules to move from/to the cytosol

Question 26

Describe the structure and features of the inter membrane space

Answer 26

Between the outer and inner membranes
▪ Similar composition of the cytosol
▪ Contains cytochrome c (inducing apoptosis)

Question 27

Describe the structure and features of the inner membrane

Answer 27

Almost impermeable to ions and small molecules.
* It contains specific transporters.
* It is folded into cristae to increase surface area

Question 28

Describe the structure and features of the matrix

Answer 28

The gel-like fluid enclosed by the inner membrane
* Has different enzymes responsible for the ATP production
* Has ribosomes & mitochondrial DNA (small circular DNA independent to the nuclear DNA)
▪ Synthesis of some mitochondrial proteins

Question 29

What evidence in mitochondrial structure is there to suggest it originated from bacteria?

Answer 29

Own Circular DNA (no histones) as prokaryotes
* Double membrane– as a cell engulfed
* Smaller ribosomes (70s like those of prokaryotic)
* Division by binary fission (like bacteria – TB2)

Question 30

What are cilia and flagella?

Answer 30

Rare hair-like extensions of the plasma
membrane (only in some human cells)

They both contain a bundle of
microtubules that gives them shape and
the association with motor proteins
allows them to beat rhythmically

Question 31

Where are flagellum found?

Answer 31

Present in spermatozoa (enabling to swim)
▪ Undulating fashion movement

Question 32

Where are cilia found?

Answer 32

• in Fallopian tubes (to push egg cells
  to the uterus through the oviduct)
• in the epithelial cells of the bronchi
  to sweep mucus and dirt out
  ▪ Beating motion like oars