Cell Ultrastructure

Question 1

Why are electron microscopes capable of a higher limit of resolution than light microscopes?

Answer 1

Electron microscopes use the wavelength of electrons (0.004nm) which is much smaller than the wavelength of visible light used by light microscopes (0.7μm)

Question 2

What is the average size of an animal cell?

Answer 2

10-20μm

Question 3

What structure within the cell has the largest membrane area?

Answer 3

(Rough) endoplasmic reticulum

Question 4

What composes the majority of the cell volume?

Answer 4

Cytosol

Question 5

What is the cytoskeleton?

Answer 5

Complex network of interlinking fibres that extend throughout the cytoplasm

Question 6

What is meant by the phospholipids within the plasma membrane being ‘amphipathic’?

Answer 6

Have both polar (hydrophilic) and non polar (hydrophobic) regions

Question 7

What are the functions of the plasma membrane?

Answer 7

• Selective permeability
• Transport of materials along cell surface
• Endo/exocytosis
• Intercellular adhesion and recognition
• Cell signalling

Question 8

What is the role of the smooth endoplasmic reticulum?

Answer 8

Lipid biosynthesis and steroidogenesis

Question 9

Where would you find cells that contain smooth ER?

Answer 9

• Liver
• Mammary gland
• Adrenal glands
• Ovaries/testes

Question 10

What is the role of the RER?

Answer 10

Protein synthesis and modification

Question 11

Describe the structure of the Golgi apparatus

Answer 11

• Stacks of flattened membrane with surrounding vesicles
• cis and trans ends (cis end receives vesicles from the RER and trans end secretes vesicles either to plasma membrane, RER or lysosomes)

Question 12

What is the role of the Golgi apparatus?

Answer 12

Modification, sorting, processing and packaging of proteins synthesised in RER

Question 13

How do lysosomes appear when stained?

Answer 13

• Dark staining

- Contain many hydrolytic/digestive enzymes

Question 14

What is a secondary lysosome?

Answer 14

Phagosome fused with a lysosome to form a PHAGOLYSOSOME

Question 15

What is the main role of peroxisomes?

Answer 15

DETOXIFICATION of molecules such as alcohol, phenols, forming acid and formaldehyde

Question 16

Where are peroxisomes found?

Answer 16

Cells of LIVER and KIDNEYS

Question 17

What are cristae?

Answer 17

Folds in the inner mitochondrial membrane which increase surface area for electron transporter proteins

Question 18

Which of the mitochondrial membranes are impermeable to small ions?

Answer 18

Inner mitochondrial membrane

Question 19

Where does the intermembrane space lie?

Answer 19

Between the outer and inner mitochondrial membranes of mitochondria

Question 20

Where does the mitochondrial DNA genome lie?

Answer 20

Within the mitochondrial matrix

Question 21

What is unusual about mitochondrial inheritance?

Answer 21

Maternal lineage only

Question 22

How is genetic information passed on through mitochondria?

Answer 22

Mitochondria contain their own genetic information within the matrix and can divide in a similar way to bacteria

Question 23

Why do mitochondria possess their own set of DNA?

Answer 23

Descendant from prokaryotes that invaded ancestral eukaryotes so contain their own DNA

Question 24

Describe the distribution of actin filaments within an animal cell

Answer 24

Arranged around the edge of the cell underlying the plasma membrane

Question 25

What is the role of intermediate filaments and where are they found?

Answer 25

• Form a tough supporting mesh work

- Found in cytoplasm and beneath the nuclear membrane forming the NUCLEAR LAMINA

Question 26

What are microtubules and where are they found?

Answer 26

• Long hollow cylinders made from TUBULIN protein

- Found at sites where structures are MOVED e.g. Cilia, flagella, mitotic spindle

Question 27

How are microtubules arranged in cilia?

Answer 27

9+2 arrangement

Question 28

Define ‘limit of resolution’

Answer 28

The minimum distance at which two objects can be distinguished