cellular anatomy #2 and viruses M1V3

Question 1

cytoskeleton - what is it?

Answer 1

• network of fibres which give the cell structure and shape, maintains organelle position
• changes constantly, felxible, but still stable

Question 2

what three different fibres does they cytoskeleton consist of

Answer 2

consists of
1. microtubules,

2. intermediate filaments
3. microfilaments

Question 3

microtubules

Answer 3

• coils of tubulin like a spring
• resists compression
• provide motility of whole cell (can form flagallae and cilia) and organelles (ATP motor proteins)

Question 4

how big are microtubles

Answer 4

• 25 nanometres wide (biggest part of cytoskeleton)

Question 5

intermediate filaments

Answer 5

• various protein cables, less dynamic
• maintain shape, anchor organelles
• form nuclear lamina

Question 6

how big are intermediate filaments

Answer 6

8-12 nanometres wide

Question 7

microfilaments

Answer 7

• double chain of protein actin
• resist tension
• network in 3D - makes cytoplasm gel like
• support movement

Question 8

types of cell junctions

Answer 8

1. Tight junction
2. Desmosomes
3. Gap junctions

Question 9

tight junction

Answer 9

prevents fluid movement, sometimes a seal

Question 10

Desmosomes

Answer 10

anchors cells together

Question 11

Gap junctions

Answer 11

where cells cytoplasms touch - things can pass through which allows intercellular communication

Question 12

Extracellular Matrix (ECM)

Answer 12

1. sometimes cells dont contact other cells - lie in ECM (mostly water)
2. Also includes glycoproteins (proteins with carbohydrate)
   - these link together to form a proteoglycan matrix - traps water, resists compression, retains shape

Question 13

what is a main type of protein in ECM

Answer 13

1. glycoproteins (proteins with carbohydrate)

- these link together to form a proteoglycan matrix - traps water, resists compression, retains shape

Question 14

what are other components of ECM

Answer 14

1. collagen
   
   • lack of vitamin c means collagen cant be formed
2. Fibronectins attach cells to ECM physically
3. Integrins allow the ECM and the cytoskeleton to communicate

Question 15

The nucleus

Answer 15

• prominent (5-10 microns)
• storage of cells genetic information and control center
• surrounded by a nuclear envelope

Question 16

nuclear lamina

Answer 16

• lines inner surface of nuclear envelope
• network of intermediate filaments
• helps maintain shape of nucleus and organize DNA

Question 17

what does defective lamina lead to

Answer 17

Hutchinson - Gilford - Progeria Syndrome (accelerated ageing)

Question 18

what are nuclear pores

Answer 18

1. holes in the nuclear envelope which allow transport in and out of the nucleus
2. RNA moves OUT of the nucleus
3. Energy, materials and signals move IN to the nucleus

Question 19

what do nuclear pores contain

Answer 19

1. Filaments on cytoplasm side

2. “basket” on nucleus side

Question 20

DNA

Answer 20

• DNA is a nucleotide polymer
• double helix structure
• humans have a lot - has to be packed efficiently - this is achieved with different levels of structure

Question 21

what is the DNA structure and terms

Answer 21

• DNA + histone proteins (“organisers”) = chromatin fibres
• within the chromtin, Histones 2 and 4 coil DNA into “bead” called nucleosome
• histone 1 causes further coiling of nucleosomes into a thicker fibre
• this fibre loops to form a thick fibre which arranges into chromosomes during cell division

Question 22

sizes of DNA (diameters)

Answer 22

• DNA helix - 2nm
• Nucleosome - 10nm
• H1 coiled fibre - 30nm
• Thick fibre - 300nm

Question 23

chromatin

Answer 23

when the cell isnt dividing some regions of chromatin are packed more tightly

Question 24

2 different types of chromatin

Answer 24

1. Heterochromatin - is more dense/ compact, and not genetically active
2. Euchromatin is less dense/ compact, and more genetically active

Question 25

viruses

Answer 25

• different to cells - not prokaryotes or eukaryotes
• viruses can infect animal, plant or even bacterial cells because they are extreamly small
• all viruses contain a nucleic acid genome, and a protein capsid that encloses it
• Many different viruses which evolve all the time

Question 26

bacteriophages

Answer 26

• viruses that infect bacteria

- most complex, but most common entity on earth

Question 27

what are the 2 different cycles of bacteriophage infection

Answer 27

1. lytic cycle (bacteria lyses/spits)

2. Lysogenic cycle

Question 28

Lytic cycle of infection

Answer 28

1. phage attaches
2. Bacterial DNA is degraded and phage DNA integrates
3. Viral genes and proteins are synthesised
4. Self assembly of parts into full phage
5. Phages release and the bacteria lyses

Question 29

Lysogenic cycle of infection

Answer 29

1. Phage DNA is replicated when bacteria divides, creating many infected bacteria
2. These bacteria contain the phage genome, called the prophage
3. The prophage can remain latent or exit the chromosomes and resume the lytic cycle

Question 30

DNA virus replication

Answer 30

1. Virus enters the cell and uncoats (capsid proteins attach to host)
2. Virus uses the host cells replicating enzymes to replicate its DNA
3. Host cell manufactures the viral proteins
4. New virus self assembles and exits from the cell

Question 31

RNA enveloped virus replication

Answer 31

• same as DNA virus replication, except in order for the RNA to be integrated into the host genome, it has to be converted to DNA by a viral enzyme called reverse transcriptase
• The viral DNA is then converted back into RNA when it replicates

Question 32

viroids and prions

Answer 32

1. Viroids are short circular loops of single stranded RNA - infect plants
2. Prions are mutated proteins that occur spontaneously but can be transmitted to other proteins