Eukaryotic Cells

Question 1

What are Eukaryotic cells?

Answer 1

Bigger and more complex than prokaryotes. Very diverse

Question 2

What are the relative sizes of Eukaryotic and Prokaryotic cells?

Answer 2

E = 10 -100 micrometres
P= 1 - 5 micorometres

Question 3

What are some features of eukaryotes?

Answer 3

• Intracellular compartmentalization (organelles)

- Nucleus

Question 4

What makes Red Blood Cells different from other eukaryotes?

Answer 4

• No nucleus
• Must have had one to begin with in order to differentiate and replicate
• Lost in when they became specialised

Question 5

Describe the structure of the nucleus.

Answer 5

• Largest organelle
• Contains most of the genetic material
• Nucleolus
• Nuclear Envelope

Question 6

Describe the function of the nucleus.

Answer 6

• Store genetic material
• DNA strands packaged with histones - condensed
• Transcription

Question 7

How does dividing trnascription and translation allow for regulation?

Answer 7

Transcription - nucleus. Translation - cytoplasm. mRNA needs to be moved. Process regulated.

Question 8

Describe the nuclear envelope

Answer 8

• Selective openings to allow mRNA out

- Some proteins may need to be moved back into the nucleus

Question 9

Describe the structure of ribosomes

Answer 9

• Ribonucleoprotein complexes

- Large and small subunits

Question 10

Describe ribosome assembly

Answer 10

• Transcription → nucleus
• Translation → cytoplasm
• Polypeptide assembled onto nascent rRNA → nucleolus
• Subunits transported to cytoplasm for function

Question 11

Describe the function of the ribosome

Answer 11

• Translate mRNA into proteins

Question 12

What happens in if the protein is destined to remain in the cytosol?

Answer 12

Translated by ribosomes free in the cytosol

Question 13

What happens if the protein is destined to be secreted?

Answer 13

• Translated by proteins on the RER

- Enter the secretory pathway

Question 14

Describe the process of translation for proteins destined to remain in the cytosol

Answer 14

• Polypeptide emerges
• Folds as its emerging from the ribosomal tunnel
• Chain grows more ribosomes attach to create a polysome
• Once a stop codon is reach the polypeptide is released

Question 15

Describe the process of translation for proteins destined to be secreted.

Answer 15

• Short hydrophpbic section emerges first
• Known as a signal peptide
• Recognised by the signal recognition peptide
• Halts translation
• Carries the ribosome to the RER
• Ribosome attaches to the RER
• Polypeptide grows again

Question 16

Outline the secretory pathway

Answer 16

Recognition of signal pathway - Golgi - Secretory Vesicles - Fused with the membrane - Released

Question 17

What is glycosylation?

Answer 17

Form of post translational modification. Addition of carbohydrates. Diverse

Question 18

Describe how post translational modification works

Answer 18

• Different enzymes are housed in different membrane bound compartments (cisternae)
• Proteins travel through in a different and specialised order
• Golgi is like an assembly line
• Cell ensures they move through in a defined order
• Receiving sequential modifications

Question 19

What is the trans golgi network?

Answer 19

• Sorting station
• Part of the endocytic pathway
• Interconnected tubules and vesicles
• Proteins trafficked through the ER are packaged into secretory vesicles that fuse with the plasma membrane to leave the cell

Question 20

What is endocytosis?

Answer 20

Taking in

Question 21

Describe endocytosis

Answer 21

Portion of plasma membranes invaginates and pinches off to form a vesicle called an endosome

Question 22

What does the lysosome do?

Answer 22

Degradative enzyme. Proteases and lipases

Question 23

What does compartmentalisation allow for?

Answer 23

• Coordination/regulation of complex of biochemical reactions
• Sequestrations of components
• Energy generation

Question 24

How do you move molecules between organelles?

Answer 24

• Vesicular transport

- Need a high level of communication

Question 25

What is autoradiography?

Answer 25

- Bio-analytical technique - helps visualise the distribution of molecules labelled with radioisotope - Can localise molecules within tissues etc - Sensitive and quantitative - Works by incorporating radioisotopes into molecuels, energy emitted can be deteced

Question 26

What is Pulse chase labelling?

Answer 26

- Incorporate radioactive isotopes into molecules synthesized during a defined time period - Radio-labelled compound added to system of choice for a brief period of time (the 'pulse') - (the 'chase') is initiated by either washing the sample to remove the isotope and/or adding excess non-labelled compound - Used to follow the dynamic of cellular processes and pathways

Question 27

Describe an a specific pulse chase labeling experiment

Answer 27

- Slices of pancreas in culture synthesisze and secrete enzyme - Add 3Hleucine become incorporated into newly synthesized proteins - After 10' wash the slices and initate 'chase' - Perform audioradiography after 0, 10 and 60 minutes

Question 28

Where do proteins enter the secretory pathway?

Answer 28

RER

Question 29

What was the SNARE hypothesis proposed to explain?

Answer 29

Specificity of vesicular transport

Question 30

What do free cell assays allow scientists to do?

Answer 30

Identify new physiological processes

Question 31

what are the 2 types of SNARe PROTEINS?

Answer 31

1. v-Snare on vesicles | 1. t-SNARE on target membranes

Question 32

describe the process of SNARE proteins.

Answer 32

- on trnasport vesicles - v SNARE recognises its partner t SNARE on appropriate target membrane - binding docks the vesicle onto target membrane and recruit machinery that meidates mebrane fusion

Question 33

what does SNARE stand for>

Answer 33

Soluble NSF attachment receptors

Question 34

outline the SNARE hypothesis

Answer 34

- a family of proteins that localize to different intracellular organelles - Transport vesicles carry specific v-SNAREs (1 mark) that recognize and bind to t-SNAREs - Membrane fusion can only proceed following formation of a functional SNARE complex

Question 35

how is molecular machinery required for membrane traffic evolutionary conserved?

Answer 35

- Sequence analysis of mammalian NSF and yeast Sec18 revealed homology - cDNA encoding NSF - complements the growth phenotype of sec18 mutant yeast

Question 36

evidence that indicates cell to cell signalling

Answer 36

single celled eukaryotes like yeast use secreted cell signals to signal mating-type during sexual reproduction