Block 2: Lecture 6. cells structure and function

Question 1

What is the main difference between eukaryotic and prokaryotic cells?

Answer 1

Eukaryotic cells have membrane-bound organelles and are much larger
Prokaryote cells lack a membrane-bound nucleus
In prokaryotes DNA is not organised within the membrane to form a nucleus
No internal membranes around organelles

Question 2

Cytoplasm

Answer 2

everything inside the plasma membrane including the organelles,
but not including the nucleus

Question 3

Cytosol

Answer 3

The fluid portion of the cytoplasm
water plus dissolved and suspended substances (eg. ions, ATP, proteins, lipids)
Does not include the organelles

Question 4

major organelles

Answer 4

Nucleus
Endoplasmic Reticulum (smooth and rough)
Golgi apparatus
Lysosomes
Mitochondria (Mitochondria do have a membrane but are not part of the endomembrane system)
Ribosomes(Ribosomes Do not have a membrane)

Question 5

The Endomembrane system

Answer 5

Nuclear envelope
Endoplasmic Reticulum (smooth and rough)
Golgi apparatus 
Lysosomes
vesicles
plasma membrane

Question 6

Plasma membrane structure

Answer 6

double layer of phospholipids with embedded proteins

Phosphoheads face the outside to the intracellular or intercellular liquid and the lipid tales are connected to each other on the inside
Much of our body is hydrophilic or “water loving”
Fats in cell membrane provide a barrier to water

Question 7

Phospholipid

Answer 7

Phospholipids are molecules with hydrophilic phosphate heads and hydrophobic lipid tails. They comprise cellular membranes, regulate certain cellular processes, and possess both stabilizing and dynamic qualities that can aid in drug delivery.
(lysosome consists of phospholipids)

Question 8

amphipathic means

Answer 8

have both hydrophilic and hydrophobic regions.

Question 9

Plasma membrane proteins

Answer 9

Integral proteins(embedded partially or fully into the membrane) eg Transmembrane protein( contact extracellular and cytoplasmic areas)

peripheral membrane proteins( can respond to receptor molecule change)

Question 10

Functions of plasma membrane proteins

Answer 10

(a) Transport(channels, transporters, general or selective, gated/not gated
(b) Enzymes. Carry out chemical reaction, specific shape interaction.

(c)Signal transduction
(Receptors .Signal transduction.
A signaling molecule will bind and will cause a change on the inside if the cell, pass a signal from the outside to the inside. Not moving the molecule, transduction and change in shape of the other side of the protein.)

(d)Cell-to-Cell recognition
Use of glycoproteins (carbohydrate + protein) as molecular signatures of the extracellular side of the cell

(e) Intercellular joining( junctions)
(f) Attachment to the cytoskeleton and ECM. eg. Fibronectin mediates contact between cell surface integrins and ECM(collagen). Inside the cell is linked to the outside of the cell–> enables movement

Question 11

cell specific & cell dynamic

Answer 11

Cell specific:
Not all cells have the same job. Protein are different in different cell types. Eg. Neurotransmitter/transport protein in the brain

Dynamic:
Even within the same time they will be responding to different conditions at that time.(influx of signal–> change in the protein representation on the outside of the cell)

Question 12

Nucleus structure

Answer 12

Enclosed by double lipid bilayer called nuclear envelope, continuous with rough ER

Entry and exit through nuclear pores

Chromatin(DNA and protein)

Question 13

Nucleus function

Answer 13

-rRNA production( assembly of small and large units of ribosomes)( in the NUCLEOLUS)

• protect DNA in eukaryotic cells
• pores regulate movement of substances( eg protein and mRNA)
• molecule segregation to allow temporal and spatial control of cell function

Question 14

How is DNA packed in the Nucleus

Answer 14

DNA wrapped 2x around group of 8 histones, to form nucleosomes collectively known as chromatin
As cell prepares for cell division, chromatin condenses further to chromatin fiber then condenses further into loops then stacks as chromosomes.

Question 15

How is DNA packed in the Nucleus

Answer 15

DNA wrapped 2x around group of 8 histones, to form nucleosomes collectively known as chromatin
As cell prepares for cell division, chromatin condenses further to chromatin fiber then condenses further into loops then stacks as chromosomes.

Question 16

Gene

Answer 16

a DNA segment that contributes to phenotype/function

Question 17

Size of cell and nucleus

Answer 17

cell: 10-20 microns
nucleus: 5-6 microns

Question 18

What stage is the cell in most of the time

Answer 18

interphase

easier for transcription to happen/access to DNA

Question 19

ribosome function

Answer 19

protein production

Where translation occurs( from mRNA)

Question 20

2 sites of ribosomal protein production in the cell

Answer 20

free in the cytoplasm making proteins to be used in cytosol (non-endomembrane destinations)
OR
attached to the RER - making non-cytosolic proteins/endomembrane

Question 21

Ribosome structure

Answer 21

large and small subunit
large-where translation occurs
made out rRNA
subunits are assembled in nucleolus and leave through nuclear pores

Question 22

Endoplasmic reticulum

Answer 22

an extensive network of tubes and tubules, stretching out from the nuclear membrane

Question 23

2 types of endoplasmic reticulum

Answer 23

rough( with ribosomes)
and smooth

lumen inside

Question 24

Rough endoplasmic reticulum

Answer 24

The major function is the production of:
• Secretory proteins
• Membrane proteins
• Organelle proteins

proteins enter the lumen within the rough ER for folding
Rough ER membrane surrounds the protein to form
transport vesicles destined for the Golgi

*most secretory proteins are glycoproteins. The carbohydrates are attached to the proteins in the ER by enzymes built into the ER membrane.

Question 25

Smooth endoplasmic reticulum

Answer 25

extends from rough ER
Lacks ribosomes: doesn’t make proteins

The major function is as a housing unit for proteins and enzymes

Synthesizes lipids, including steroids and phospholipids
Metabolism of carbohydrates

Storage of cell-specific proteins, not all cells make all proteins
(Examples:
Liver: houses enzymes for detoxification(drugs and poisons) and for glucose release Muscle: calcium ions )

Functions are tissue-specific

Question 26

golgi apparatus structure

Answer 26

made up of 3-20 flattened membranous sacs called cisternae, stacked on top of one another (“pita bread”)

trans- “shipping side of Golgi)
cis-“receiving side of Golgi”

*cisternal maturation- the cisternae progress forward from the cis to trans face carrying and modifying the cargo as they move.

Question 27

golgi apparatus function

Answer 27

Functions:
modify, sort, package and transport proteins received from the rough ER using enzymes in each cisternae

Modifications occur within each sac
(formation of glycoproteins, glycolipids and lipoproteins)

Formation of:
• secretory vesicles (proteins for exocytosis)
• membrane vesicles (PM molecules)
• transport vesicles (molecules to lysosome)

Question 28

Lysosomes features and functions

Answer 28

vesicles formed from golgi membrane
membrane proteins pump H+ in to maintain acidic pH inside the lysosome

Main function is digestion of:
• substances that enter a cell
• cell components e.g. organelles - autophagy
• entire cells - autolysis

Question 29

Mitochondria structure

Answer 29

Mitochondria are made up of:
• Outer mitochondrial membrane
• Inner mitochondrial membrane, with folds called cristae
• Fluid filled interior cavity, called the mitochondrial matrix

Have their own ribosomes. Have their own genome where they can encode mitochondrial specific products

Question 30

Mitochondria function

Answer 30

Produce ATP

*The more energy a cell requires, the more ATP it must make, and the greater the number of mitochondria present

Question 31

Cytoskeleton

Answer 31

Fibres or filaments that help to maintain the size, shape and integrity of the cell:
•Act as scaffolding across the cell
•Involved in intracellular transportation and cell movement

Question 32

3 types of fibers in cytoskeleton

Answer 32

Microfilaments
Intermediate filaments
Microtubules
(smallest to largest)

Question 33

Microfilaments(cytoskeleton)

Answer 33

Diameter: 7 nm
Comprised of actin molecules assembled in two long chains, twisted around each other

Found around the periphery and lining the interior of the cell

Function:
Bear tension and weight by anchoring the cytoskeleton to plasma membrane proteins, and promote amoeboid motility if required (eg. macrophage)
Assembled and disassembled as required – they are dynamic(Do not stay the same, the cell will have different amounts of microfilaments)

Cell motility. Especially as a part of the contractile apparatus of muscle cells.(actin thin filaments)

Question 34

Intermediate filaments(cytoskeleton)

Answer 34

Diameter: 8-12 nm.
Comprised of a diverse range of different materials; one example: is keratin Found in the cytoplasm of the cell.

Function:
• bear tension and weight throughout the cell, e.g., during cell anchoring,
• act as a scaffold for cellular organelles, e.g., the nucleus. Keeps organelles in place.

Usually the most permanent of the cytoskeleton -scaffold does not need to change

Question 35

Microtubules( cytoskeleton)

Answer 35

Diameter: tubular structure, 25 nm with the central lumen of 15 nm diameter
Comprised of tubulin dimers (alpha and beta), coiled, to form a tube

Extends from centriole into cytoplasm/nucleus

Functions:
• Support cell shape and size
• Guide for movement of organelles,
e.g., vesicles from Golgi to membrane
• Chromosome organization – cell division
• Support and movement of cilia /flagella
Assembled and disassembled as required - are dynamic

Question 36

nuclear lamina

Answer 36

the netlike lamina lines the inner surface of the nuclear envelope

Question 37

Give an example of cells that would have large number of ribosomes based on the ribosome function

Answer 37

pancreas( production of enzymes–> high production of proteins needed)

Question 38

Proteins made in ribosomes in cytosol vs ER

Answer 38

Most of the proteins made on free ribosomes function within the cytosol, e.g enzymes that catalyze the first steps of sugar breakdown.

Bound ribosomes generally make proteins that are destined for insertion into membranes, for packaging within certain organelles such as lysosomes, or export from the cell(secretion).

Question 39

centrosome

Answer 39

microtubule organizing center. Within the centrosome, there is a pair of centrioles
Before an animal cell divides the centrioles replicate.

Question 40

where are ribosomal subunits synthesized and assembled?

Answer 40

nucleolus