Topic 2.1 - Structure of eukaryote and prokaryote cells

Question 1

List three ways eukaryotic cells differ from prokaryotic cells.

Answer 1

membrane bound organelles

DNA is enclosed in a nucleus

Have larger ribosomes (80S) than prokaryotic cells

Has a murein cell wall, a capsule and plasmid

Question 2

Function of nucleus

Answer 2

containing chromosomes, consisting of protein-bound(histones) , linear DNA within the nucleoplasm.

Question 3

Function of nuclear envelope

Answer 3

Double membrane surrounding the nucleus with nuclear pores to let molecules in and out

Question 4

Plasma

Membrane

Answer 4

Involved in the transport of substances via diffusion or facilitated diffusion, active transport

Question 5

Cytoplasm

Answer 5

Where chemical reactions take place

Question 6

Ribosome

Answer 6

Where amino acids are joined together to make proteins (i.e. protein synthesis)

Question 7

Mitochondria

Answer 7

Site of AEROBIC respiration

Produces ATP (releases energy)

Contains short, circular DNA (not associated with proteins)

Has a double membrane. The inner membrane is folded forming cristae.

Contains smaller (70S) ribosomes

Question 8

Rough Endoplasmic Reticulum (RER)

Answer 8

Has ribosomes on their surface which are involved in protein synthesis

Proteins are also folded up inside the RER

Question 9

Smooth endoplasmic reticulum

Answer 9

Synthesis and storage of molecules such as lipids, steroids and sterols

Question 10

Golgi Apparatus and golgi vesicles

Answer 10

Modifies proteins (e.g. by adding carbohydrate groups to form a glycoprotein or lipid groups to make a lipoprotein)

Stores proteins

Packages proteins into vesicles

Transport vesicles to cell surface

Question 11

Lysosomes

Answer 11

A vesicle that contains hydrolytic enzymes (lysozymes) which are used to digest molecules

Question 12

Chloroplast

Answer 12

Chlorophyll absorb light for photosynthesis to produce carbohydrates

Has a double membrane. Inside there are thylakoid membranes which can form a stack called a granum (pl. grana). The grana are linked by lamellae.

Contain starch grains

Question 13

Define resolution

Answer 13

Resolution is the minimum distance apart that the two objects can be in order for them to appear as separate items.

Question 14

Describe the procedure to prepare a slide

Answer 14

Add a drop of water to the slide

Remove a thin section of tissue and place it onto the slide (flat as possible)

Add 1 drop of iodine dissolved in potassium iodide to stain the sample (This is only correct if it is plant tissue)

Lower a coverslip on top using a mounting needle

Question 15

Explain why it was important that the sections of tissue were thin

Answer 15

A thin section allows more light through;

allows a single layer of cells to be viewed.

Question 16

Why are electron microscopes used to view cells?

Answer 16

They have a HIGH resolution

because electrons have a shorter wavelength than light.

This allows you to view internal structures/organelles of a cell.

(Remember using this – Light microscope = Low resolution = Longer wavelength)

Question 17

Name two structures in a eukaryotic cell that cannot be identified using an optical microscope.

Answer 17

Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface membrane

Question 18

Describe the limitations of using a transmission electron microscope to investigate cell structure.

Answer 18

Cannot look at living material / Must be in a vacuum;

 Specimen must be (very) thin;

Artefacts present;

Complex staining method / complex / long preparation time;

 Image not in 3D / only 2D images produced.

Question 19

Write an equation to calculate magnification

Answer 19

Magnification = Image length / Actual Length

Question 20

What is meant by ‘cell fractionation

Answer 20

Separating out the contents of a cell into the different ‘fractions’ (i.e. different parts).

This usually means separating out the different organelles by DENSITY.

This is useful for scientists because it allows them to study individual organelles

Question 21

What is homogenisation?

Answer 21

Using a blender (or a homogenizer) to break open the cell membrane to release all of the organelles inside

Question 22

Why is the solution filtered?

Answer 22

To remove any whole cells or large cell debris

Question 23

Why is it cold?

Answer 23

To reduce enzyme activity TO prevent digestion of organelles

Question 24

Why is it isotonic?

Answer 24

To prevent osmosis, SO that the ORGANELLES do not shrivel or burst/ lysis

Question 25

Why is it buffered?

Answer 25

So that the pH is kept constant, SO that proteins/ enzymes are not denatured

Question 26

What does ultracentrifugation mean?

Answer 26

Ultracentrifugation is used to separate very small things – such as different lengths of DNA/RNA

The sample is put into a tube

It is spun at a low speed (low Revolutions Per Minute = RPM)

The most dense organelle forms a sediment/pellet at the bottom of the test tube

The other organelles remain suspended in the supernatant

The supernatant is removed and put into a clean test tube and spun at higher speed

The second most dense organelle forms a sediment at the bottom etc