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Cells > Mod1 - Cells and their Components > Flashcards

Mod1 - Cells and their Components Flashcards

1
Q

What three things does Cell Theory state?

A
  1. Cells are the fundamental units of life
  2. All organisms are composed of cells
  3. All cells come from pre-existing cells
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2
Q

Three key differences between prokaryotes and eukaryotes

A
  1. Prokaryotes have no nucleus (DNA floats freely in the cell)
  2. Prokaryotes have no (or rudimentary) internal membranes
  3. Prokaryotes have very basic cytoskeleton, while eukaryotes have extensive cytoskeleton
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3
Q

What does the Endoplasmic reticulum make?

A

Secretory and membrane proteins; lipids

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4
Q

Describe the structure of the Endoplasmic Reticulum

A

A network of interconnected spaces enclosed by a single membrane that is continuous with the nuclear envelope

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5
Q

In what parts of the body is Smooth ER abundant?

A

Cells active in lipid metabolism, and in the liver (detoxification of lipid-soluble compounds)

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6
Q

What is the sacroplasmic reticulum?

A

An ER-derived calcium store in muscle cells (important role during muscle contraction)

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7
Q

What are the roles of the Golgi apparatus?

A

Modification of cargo (e.g. glycosylation) and Sorting of Cargo to the correct location

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8
Q

What 3 functions (mentioned in the lecture) occur in the Cytosol?

A
  1. Protein synthesis and degradation
  2. Intermediary metabolism (e.g., glycolysis)
  3. Location of the Cytoskeleton
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9
Q

What is the main model organism for prokaryotes?

A

E. coli

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10
Q

What are the main model organisms for lower eukaryotes?

A

S. cerevisae (budding yeast) and S. pombe (fission yeast)

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11
Q

What is the model cell system for higher eukaryotes?

A

Vertebrate cells in culture

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12
Q

What is the model organism for vertebrate development?

A

Zebrafish

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13
Q

What is the model organism for classical genetics and development?

A

Drosophila melanogaster

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14
Q

What is the model organism for genome sequencing and programmed cell death?

A

Caenorhabditis elegans (nematode)

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15
Q

What is the model organism for plant molecular biology and development?

A

Arabidopsis thaliana

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16
Q

Where specifically can a disulphide bond form?

A

Between two cysteine side chains in a protein

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17
Q

What type of post-translational modifications can occur on Uncharged Polar side chains?

A

N-glycosylation, O-glycosylation, Phosphorylation

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18
Q

What are the functions of fast vs slow hydrolysis of nucleotides in controlling protein shape/activity?

A

Fast hydrolysis of ATP drives movement
Slower hydrolysis of ATP or GTP gives a switch activity

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19
Q

What can phosphorylation do to protein activity?

A

Turn it on OR off

20
Q

Transmitted light microscopy can magnify cells up to how many times? (And what resolution)?

A

1000X, 0.2 micrometres

21
Q

What is a disadvantage of using Antibody-coupled dyes to detect specific proteins in cells?

A

This technique can only be used with chemically fixed (DEAD) cells

22
Q

What type of light microscopy allows imaging of 3D samples and “super-resolution”

A

Advanced fluorescence light microscopy

23
Q

Which protein can be attached to a specific protein as a tag for fluorescence microscopy

A

Green Fluorescent Protein (GFP)

24
Q

What are the four “fractions” obtained through differential centrifugation of a eukaryotic cell

A

Pellet 1 = nuclei (heaviest)
Pellet 2 = mitochondria
Pellet 3 = ER and Golgi
Supernatant = Cytosol

25
Q

What is the “default” destination for proteins without signal sequences (and how many proteins end up there)?

A

Cytosol (70%)

26
Q

What are the 5 general ‘rules’ for protein targeting?

A
  1. Signal (to target the protein to the correct subcellular destination)
  2. Receptor(s) that recognise these signals
  3. Protein unfolded/loosely folded to cross the membrane
  4. Translocation machinery allowing proteins to cross the membrane or be inserted into it
  5. Energy (e.g. ATP/GTP)
27
Q

Which types of amino acids are commonly found in Nuclear Location Signals (and two examples)

A

Positively charged (basic) amino acids - e.g. Arg/Lys

28
Q

Are signal sequences removed from proteins once they reach their destination?

A

Some can be, but NOT the Nuclear Location Signal

29
Q

How are proteins imported into the nucleus? (Steps)

A
  1. Nuclear Import Receptor binds to NLS-containing proteins in the cytosol
  2. Fibrils direct receptor to pore
  3. Receptors bind pore proteins
  4. Cargo proteins moved into nucleus
30
Q

Which small GTPase drives nuclear import?

A

Ran

31
Q

What role do the two regulatory proteins play in altering Ran conformation?

A

Reg Protein 1 (GAP) triggers GTP hydrolysis
Reg Protein 2 (GEF) promotes exchange of GDP for GTP

32
Q

What role does Ran play in nuclear import of proteins?

A

Inside the nucleus, Ran-GTP binds to the receptor, displacing the cargo protein

33
Q

What is one example of a transcription factor family whose nuclear import/export is regulated by Calcium?

A

Nuclear Factor of Activated T-Cells (NFAT)

34
Q

What types of amino acids are commonly found in an ER SIGNAL SEQUENCE? (And 3 examples)

A

8+ hydrophobic amino acids (e.g., leucine, isoleucine, valine)
Note: usually near the N-terminus

35
Q

What are the names of the particle and translocator involved in ER Targeting?

A

Signal Recognition Particle (SRP) and Sec61 Translocator

36
Q

What is the most extensive membrane system in eukaryotic cells?

A

The Endoplasmic Reticulum

37
Q

Describe the process of co-translational translocation of secretory proteins into the ER Lumen

A

As the protein is produced by a ribosome, the N-terminal signal sequence binds the Se61 translocator, opening the channel

Protein is threaded through the channel as a loop while translation is occuring

A signal peptidase cleaves the signal, leaving it as a stub in the cytoplasm and releasing the protein in ER

38
Q

What is the initial step that occurs for all membrane proteins except mitochondrial ones (i.e. lysosomal, endosomal, Golgi and plasma)?

A

They are inserted into the ER membrane, with part of the protein in the lumen and part in the cytosol

39
Q

Why/how do lysosomal/endosomal/Golgi/plasma membrane proteins get embedded in the ER membrane, instead of passing through like ER-destined proteins do?

A

In addition to the signal sequence which binds Sec61, these proteins have a hydrophobic Stop Transfer Sequence - this stops translocation when it reaches Sec61, and acts as a transmembrane domain to anchor the protein in the bilayer

40
Q

How are multi-pass membrane proteins formed?

A

Alternation of internal Start Transfer sequences (which remain in the membrane, unlike N-terminal ones), and Stop Transfer sequences

41
Q

What are the common key defining features of ALL ER Signal Sequences?

A

ALL ARE HYDROPHOBIC, ALL BIND SEC61 TRANSLOCATOR

42
Q

Describe the nature of Mitochondrial Signal Sequences

A
  1. Normally a high content of Arg, and Ser/Thr
  2. 20-80 amino acids long, at N terminus
  3. Usually cleaved after import into matrix
43
Q

Describe the secondary structure of Mitochondrial Signal Sequences

A

They form an amphipathic alpha helix (positively charged residues on one side, non-polar ones on the other)

44
Q

Summarise the steps involved in transporting a Mitochondrial protein into the matrix

A
  1. Signal Sequence recognised by receptor in the OMM
  2. Translocator channel moves protein into IMS
  3. Signal binds a SECOND translocator in IMM
    (Note: protein must unfold so it can pass through both membranes at the same time)
45
Q

Describe the role of chaperone proteins in Mitochondrial Protein import

A

Hsp70s (chaperones) pull protein into the matrix and help to refold it - driven by ATP hydrolysis (very different system from Ran in nucleus)

46
Q

Describe the nature of chloroplast signal sequences

A

N-terminal, rich in Ser/Thr and small hydrophobic amino acids; usually cleaved after import into stroma

47
Q

What can “cut and paste” experiments reveal about signal sequences?

A

If they are Necessary, and if they are Sufficient:

If removing a signal sequence causes a protein to be mislocalised, the sequence is Necessary

If adding the signal to a cytosolic protein causes it to be localised, the sequence is Sufficient

Cells (8 decks)

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