Bevington 2 organelles

Question 1

Extracellular:

Answer 1

outside the cell

Question 2

Intracellular:

Answer 2

inside the cell

Question 3

Intercellular

Answer 3

(spanning or moving) between two cells

Question 4

Differences between lipid composition in membranes of Eukaryotes, Bacteria and Archaea

Answer 4

• Eukaryotes = cholesterol
• Bacteria = phosphatidylethanolamine
• Archaea= phos

Question 5

PLASMA MEMBRANE : STRUCTURE

Answer 5

	Variable thickness
	Patchy
	High level of proteins
	May not be very ‘fluid’
	Stiff regions => lipid rafts

Question 6

PLASMA MEMBRANE :

FUNCTION

Answer 6

• Impermeable to water & water-soluble molecules = sugars amino a. & ions
• Self healing = cannot tear, rapidly re-seals
• Signalling & transport - embedded proteins (receptors, ion-channels) = intergral proteins
• Cell recognition - cell surface molecules = about environment => cell surface/extracellular materials

Question 7

EXTRACELLULAR STURCTURE

EUKARYOTES

Answer 7

• Protein uses energy of absorbed light to pump H+ ions out of cell through a trans-membrane channel lined w/ helical segments of polypeptide chain

Question 8

BACTERIAL CELL MEMBRANES & WALLS

Answer 8

+/ve covalently attach to amino modified sugars

-/ve small peptidoglycan

Question 9

Gram negative bacterial cell wall

e.g

Answer 9

e.g. Escherichia coli (E. coli)

A double lipid bilayer

Question 10

Lipopolysaccharide:

Answer 10

recognised by immunisystem triggering a potent inflammatory response.

Question 11

CAPSULE:

Answer 11

An additional thick polysaccharide layer secreted by some bacteria as an additional defensive layer
are resistant to phagocytosis by monocytes & macrophages

Question 12

PLANT CELL WALL: STRUCTURE

Answer 12

• Primary cell wall: parallel aligned fibres (flexible = deposited during growth)
• Secondary cell wall: Non-aligned fibres (rigid = deposited once growth has stopped)
• Middle lamellae: Sticky layer of polysaccharides (pectins) hold adjacent cells together.

Question 13

PLANT CELL WALL:

FUNCTION

Answer 13

• Inert: barrier, regulates entry/exit of substances
• Rigid (non-aligned fibres): Maintains shape despite movement of water
• Flexible (parallel aligned fibres of the primary cell wall): allow growth

Question 14

PLANTS
EXTRACELLULAR MATRIX (ECM)
STRUCTURE

Answer 14

Made up of glycoproteins of different classes
• Fibronectin (binds to integrin proteins in membrane)
• Collagen (binds to fibronectin)
• Proteoglycans (bind to fibronectin)

Question 15

PLANTS
EXTRACELLULAR MATRIX (ECM)
FUNCTION

Answer 15

• Forms gel :=mechanical protection in tissues
• Flexible: allows changes in shape & size.
• Communication: Integrins can transmit signals between ECM and the inside of the cell
• Signalling can influence gene expression = Affects cell function & differentiation (see Lecture 6).

Question 16

RIBOSOMES

FUNCTION

Answer 16

in cytosol / Rough Endoplasmic Reticulum
- Molecular machine (a complex of proteins & ribosomal RNAs (rRNAs)) translates a messenger RNA (mRNA) nucleotide sequence into a protein amino acid sequence

Question 17

Prokaryotes

Ribosome structure

Answer 17

70S Ribosomes (so do mitochondria and chloroplasts, consistent with the hypothesis that they evolved from bacteria that colonised primordial eukaryotes).

Question 18

Eukaryotes

Ribosome structure

Answer 18

80S ribosomes (as do archaebacteria, suggesting they are more closely related to each other than to prokaryotes).

Question 19

NUCLEUS STRUCTURE

Answer 19

• Nuclear envelope: Evolved from involution of plasma membrane
• Double lipid bilayer separated by 20-40nm space
• Many Pore complexes made from proteins embedded in membrane
• Inner membrane lined by nuclear lamina
• Intermediate filaments

Question 20

NUCLEUS FUNCTION

Answer 20

• Contains most genes in the eukaryotic cell.
• Mitochondria & chloroplasts have own DNA
• Chromosomes: single molecule of DNA
• Pore complex: controls entry & exit of proteins, RNA &macromolecules
• Nuclear lamina: maintains shape of nucleus
• Nucleolus: synthesis of rRNA & assembly into ribosomal subunits

Question 21

CHLOROPLASTS STRUCTURE

Answer 21

• hypothetical endocytosis of photosynthetic bacteria (early in the evolution of plant cells) may explain why choroplasts (like mitochondria) have 2 lipid bilayers surrounding them.
• Photosynthetic prokaryotes have invaginations of their plasma membranes called thylakoids that form a large surface area for photosynthesis.

Question 22

CHLOROPLASTS FUNCTION

Answer 22

•	3 lipid bilayer membranes:
o	Outer membrane
o	Inner membrane
o	Thylakoid membrane
•	3 regions divided by membranes:
o	Inter membrane space: Regulation of protein transport to/from organelle by protein complexes in membrane
o	Stroma: Light independent reactions
o	Thylakoid space: Chlorophyll