eukaryotic cell part I

Question 1

what are sphingolipids

Answer 1

a constituent of the plasma membrane which contain
1) sphingomyelins which contain a phosphocholine head group
2) glucosylcerebroside= a sphingolipid with a glucose

Question 2

what are the cellular components of the cell responsible for

Answer 2

the coordinated and efficient function of the cell including providing shape and support, locomotion and reproduction

Question 3

how can cellular components be classified

Answer 3

1) double membrane bound organelles
2) Single membrane bound organelles
3) cellular components without membrane

Question 4

define organelle

Answer 4

membrane bound compartments or structures in a cell that perform a special function
the name means ‘little organ’

Question 5

what are some double membrane bound organelles

Answer 5

1) nucleus
2) mitochondria
3) chloroplasts

Question 6

what are some single membrane bound organelles

Answer 6

1) vacuole
2) lysosome
3) golgi apparatus
4) ER
5) peroxiomes
6) vesicles

Question 7

what are some cellular compartments without a membrane

Answer 7

1) cell wall
2) ribosomes
3) cytoskeleton

Question 8

what does the nucleus consist of

Answer 8

1) nuclear envelope
2) nucleoplasm
3) nuclear lamina
4) chromosomes and chromatin
5) nucleolus

Question 9

what is the structure of the nuclear envelope

Answer 9

two membranes of phospholipid bilayers with idfferent proteins
the inner membrane defines the nucleus whilst the outer is continous with the RER
the nuclear pores is where the two membranes fuse

Question 10

outline the nuclear pore

Answer 10

• ring like complexes composed of specific membrane proteins where material moves
• made up of multiple copies of different proteins called nucleoproteins which help cargo proteins through the pore

Question 11

outline how larger proteins transverse through the nuclear pore

Answer 11

ribonucleoprotein and large proteins need the assistance of soluable transporter proteins

Question 12

what is the nucleoplasm

Answer 12

suspends structures within the nucleus which are not membrane bound e.g. chromosomes
it is referred to as the karyoplasm or nuclear sap and contains many proteins

Question 13

how does the nuceloplasm maintain the shape of the nucleus

Answer 13

protein fibres form a crisscross matrix within the nucleus

Question 14

what is the nuclear lamina

Answer 14

• a protein mesh associated with the inner face of the inner membrane which provides mechanical support
• proteins called lamins form a 2D netowrk allong the inner surface of the membrane giving it its shape

Question 15

what are chromosomes and chromatin

Answer 15

chromosomes conatin the genetic material where DNA is wrapped around histones into the nucleosomes
nucleosomes fold up to form chromatin fibre which is packed into chromosomes

Question 16

what does chromatin divide into

Answer 16

1) euchromatin
2) heterochromatin
these represent two different degrees of DNA condensation (the least condensed sate appears loosley distributed in the nucleus)

Question 17

what are the two forms of heterochromatin

Answer 17

1) constitutive= always remains heterochromatic
2) faculative= regions of euchromatin are converted to the heterochromatic state and silenced by deacetylation

Question 18

what is the nucleolus

Answer 18

nucleus site of DNA replication and RNA transcription and processing
the sit ribosomal RNA synthesis and ribosome biogenesis

Question 19

how are proteins transported in the nucleus

Answer 19

1) all proteins synthesised in the cytoplasm are imported into the nucleus by the nuclear pore complexes
2) these proteins contain nuclear localisation signals which direct their transport into the nucleus

Question 20

what is the role of GTPase Ran in the transport of proteins

Answer 20

regulates interaction of transport receptors with cellular cargo proteins

Question 21

what is the tole of Ran in the transport fo proteins

Answer 21

a monomeric G protein which acts as a molecular switch existing in two conformations
1) Ran+GDP
2)Ran+GTP

Question 22

outline the process of nuclear import

Answer 22

1) importin binds to cargo protein
2) cargo complex diffuses through the nuclear pore
3) RanGTP interacts with importin causing conformational change which decreases affinity for cargo protein releasing it
4) importin RanFTP bind forming a complexand is exported back into the cytoplam
5) RanFTP is hydrolysed to RanGDP causing dissociation of importin
6) RanGDP is returned to nuceloplams by nuclear transport factor 2
7) guanin nucleotide exchange factor releases GDP and rebinding of GTP

Question 23

outline the process of nuclear export

Answer 23

1) exportin 1 binds to the NES of the cargo protein to be transported with Ran-GTP
2) cargo complez diffuses thorugh NPC
3) GTPas activating protein converts RanGTP to Ran GDP
4) conformational change in Ran leads to dissociation of cargo complex
5) NES containing cargo protein relased into cytosol and exportin1 and RAnGDP go back to nucleus
6) GEF cuases felease and binding of GDP to GTP

Question 24

what does NES and NLS stand for

Answer 24

NES= nuclear exporting signal
NLS= nuclear localisation siganl

Question 25

what is needed for nuclear export

Answer 25

protiens need both NES and NLS signals

Question 26

outline the process of nuclear export

Answer 26

1) exportin 1 binds to the NES of the cargo protein as well as the Ran-GTP forming a cargo complex
2) the cargo complex diffuses through the Nuclear pore complex
3) GTPase-activating protein converts Ran-GTP to GDP
4) this conformational change leads to dissociation of cargo complex
5) NES cargo protein is released into cystol and exportin and RanGDP are transported back to nucleus by NTF2
6) GEF cuases release of GDP and rebinding of GTP

Question 27

what molecules hydrolyses Ran-GTP to GDP

Answer 27

GTPase-activating protein (GAP)

Question 28

what causes the rebinding of Ran-GDP to GTP

Answer 28

guanine nucleotide exchange factor (GEF)

Question 29

outline the process of the export of mRNA out the nucleus

Answer 29

1) mRNA remains associated with the specific heterogenic nuclear ribonucleoproteins in the messenger ribonuclear protein complex
2) an mRNA- exporter binds to the protein complex and diffuses through the nuclear pore