2.4 Eukaryotic cell structure

Question 1

What is a lysosomes and why is the membrane that surrounds it so important?

Answer 1

Lysosomes are specialised vesicles (1)
that contain hydrolytic enzymes (1)
for breaking down waste material.
The membrane that forms lysosomes has an important role in compartmentalising these enzymes away from cell structures that could be damaged by activity of the enzyme (1).

Question 2

Explain why cells need to be compartmentalised, and describe three examples of compartmentalisation within an animal cell

Answer 2

Incompatible reactions / catabolic and anabolic reactions require different conditions / damage due to hydrolytic enzymes (3)

three named examples (e.g. nucleus, vesicle, lysosome, mitochondrion, Golgi body, endoplasmic reticulum, chloroplast) (1).

Question 3

Compare the structure and function of the rough and smooth endoplasmic reticulum

Answer 3

Rough ER has ribosomes attached and smooth ER does not have ribosomes attached (1);
rough ER protein synthesis (and modification) (1);
smooth ER lipid synthesis (1).

Question 4

Describe the structure and function of the cytoskeleton

Answer 4

The cytoskeleton has three components: microfilaments (1)
are contractile fibres made of actin that bring about cell contraction during cytokinesis (1);

microtubules (1)
are formed from the cylindrical protein tubulin and form scaffold like structures used both in the movement of organelles and vesicles and as spindle fibres in the segregation of chromosomes/chromatids in cell division (1);

intermediate fibres give mechanical strength to cells (1).

Question 5

Discuss how the structure of microfilament and microtubules means these components of the cytoskeleton are involved in the movement of cells but the intermediate fibres are not.

Answer 5

microfilaments composed of actin (1) /
(actin is) contractile (1) /
microtubules composed of tubulin (1) /
(tubulin) polymerises (1) /
(contraction and polymerisation lead to) change in length of filaments (1) /
change in length (of filaments) results in movement of cell (1) /
intermediate fibres have fixed length (1) / for stability (1)

Question 6

Protein synthesis
level 3 answer

Answer 6

Firstly, mRNA is produced in the nucleus which carries the code for the protein, and it leaves the nucleus through the nuclear pores.​

Once it reaches the ribosomes, the proteins will be synthesized and then processed by the rough endoplasmic reticulum.​

From the rough ER, the proteins will be packaged into transport vesicles and travel to the golgi apparatus, using microtubules as tracks for movement.​

The Golgi apparatus will then modify and package the proteins into secretory vesicles which will move to the cell surface membrane using the cytoskeleton.​

The secretory vesicles will fuse with the cell surface membrane and release the protein out of the cell by exocytosis.

Question 7

protein synthesis
steps

Answer 7

MRNA leaves nucleus through nuclear envelope.​
Protein synthesis occurs in ribosome.​
Proteins are packaged into transport vesicles.​
Travel to Golgi apparatus​
Using microtubules are tracks.​
Protein are modified are packaged into secretory vesicles.​
Secretory vesicles move through the cytoskeleton to cell surface membrane.​
Fuse to cell surface membrane and proteins are released by exocytosis.

Question 8

Protein synthesis
detailed

Answer 8

MRNA produced in nucleus​
Carries the code for protein ​
Leaves nucleus through nuclear pores​

When reaches ribosomes​
Proteins will be synthesized​
And then processed by the RER​

From RER​
Proteins packaged into transport vesicles​
Travel to Golgi apparatus​
Using microtubules as tracks for movement.​

Golgi apparatus​
Modify and package proteins​
Into secretory vesicles​

Move to the cell surface membrane​
Using the cytoskeleton​

Secretory vesicles​
Fuse with ​
Cell surface membrane​

Release protein ​
Out of the cell by exocytosis.

Question 9

Nucleus

Answer 9

Controls activities of cells and contains DNA.

Question 10

Chromatin

Answer 10

Consist of DNA wrapped around histone proteins.

Question 11

Nucleolus

Answer 11

Makes RNA and ribosomes.

Question 12

Nuclear envelope

Answer 12

Contains pores that control what enters and leaves the nucleus.
E.g RNA and ribosomes

Question 13

Mitochondria

Answer 13

Site of aerobic respiration which produces ATP.

Double membrane
Inner membrane is folded to form a structure called cristae.
The fluid inferior is called the matrix,

Membrane forming the cristae contains enzymes used in aerobic respiration.

Question 14

Vesicles

Answer 14

Membrane bound sacs for transport and storage.

Question 15

Lysosomes

Answer 15

Specialised vesicles.
Spherical sacs surrounded by a single membrane.
Contains powerful digestive enzymes.
Role is to break down materials.

Question 16

Ribosomes

Answer 16

Site of protein synthesis.

Each ribosome consists of two subunits.
Not membrane bound organelles (prokaryote + eukaryotes)

Can be free floating in the cytoplasm or attached to the RER.
Constructed of RNA molecules made in the nucleus.

Question 17

Endoplasmic reticulum

Answer 17

Consists of a series of flattened membrane bound sacs called cisternae.

RER:
Studded with ribosomes
Processes proteins
SER
No ribosomes
Synthesis and process of lipids and carbohydrates.

Question 18

Golgi apparatus

Answer 18

Stack of membrane bounded flattened sacs.

Packages (into vesicles) and modifies proteins.
Production of lysosomes.

Question 19

centrioles

Answer 19

Self replicating organelles made up of 9 bundles of microtubules.
Help in organising cell division.
Only found in animal cells.

Question 20

Flagella and cilia

Answer 20

Flagella and cilia

Both are extensions that protrude from some cell types.
Flagella are longer.
Cilia are usually present in greater numbers.

Use to move fluids along membrane.

Flagella
Stick out from teh cell surface.
Surrounded by the plasma membrane.

9+2 formation.

Microtubules contract to make the flagellum move.
Used to propel cells forward (e.g. sperm)

Cillia
Small, hair like structures found on the surface membrane of some animal cells.

9+2 formation (ring of 9 protein microtubules inside, 2 in the middle)

Microtubules allow the cillia to move substances along the cell surface.

Question 21

The cytoskeleton

Answer 21

(Function: support structure and movement)

microfialment
microtubules
intermeddiate fibres

Question 22

Microfilaments

Answer 22

Contractile fibres formed from the protein actin.
Responsible for cell movement and also cell contraction during cytokinesis.

Question 23

Microtubules

Answer 23

Globular tubulin proteins polymerise
To from tubes that are used to form scaffold-like structure
That determines the shape of the cell.

Also acts as tracks for the movement of organelles.

Spindle fibres, which separate chromosomes in cell division, are composed of microtubules.

Question 24

Intermediate fibres

Answer 24

Give mechanical strength to cells
Help maintain their integrity.

Question 25

end of 2.4