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Phase 1 - Week 1 > Cells And Organelles > Flashcards

Cells And Organelles Flashcards

1
Q

List the major organelles/sub cellular structures of a typical human cell.

A
  • plasma membrane
  • nucleus
  • cytoskeleton
  • mitochondria
  • free ribosomes
  • Golgi apparatus
  • endoplasmic reticulum
  • rough endoplasmic reticulum
  • lysosomes
  • peroxisomes
  • endosomes
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2
Q

Describe the structure of the plasma membrane of a typical human cell.

A
  • phospholipid bilayer
  • proteins dotted throughout (transmembranous and peripheral)
  • cholesterol molecules
  • carbohydrates
  • amphipathic
  • semi-permeable
  • fluid mosaic model
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3
Q

What are the functions of the plasma membrane of a typical human cell?

A
  • regulate entry and exit from the cell
  • cell signalling
  • support (attachment to ECM or cytoskeleton)
  • site for enzyme activity
  • form membrane for sub-cellular organelles
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4
Q

How does the plasma membrane interact with the extracellular environment?

A
  1. Through integral plasma membrane proteins:
    • allow transfer of small molecules across the membrane
    • through pumps, carriers, channels
  2. Through plasma membrane receptors:
    • interact with a specific ligand
    • initiate a cascade of chemical signals in the cell
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5
Q

Discuss the composition and function of the nucleus.

A

Composition:

  • bound by a double membrane/nuclear envelope
  • DNA packaged as chromatin
  • nuclear pore facilitates entry and exit to nucleus
  • membrane supported by nuclear lamina
  • nucleolus

Function:

  • nucleolus synthesises rRNA and ribosomes
  • DNA replication (mRNA)
  • gene expression (transcription/post-transcriptional modification)
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6
Q

Why is it important that the cell compartmentalises into different organelles?

A
  • to provide a permissive environment for a set of biochemical functions
  • to protect the cell by segregating destructive enzymes and chemicals
  • to localise cellular processes for efficient functioning
  • to separate molecules required for specific functions
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7
Q

Describe the structure of mitochondria.

A

Outer membrane:
- contains portions? (Proteins which allow movements of ions in and out of mitochondrion)
- also contains enzymes involved in elongation of fatty acids and oxidation of adrenaline
Inner membrane:
- folded into cristae to increase SA available for ATP production
- contains enzyme ATP synthase which generates ATP in matrix
- contains transport proteins that regulate movement of metabolites into and out of matrix
Inter membrane space:
- space between outer/inner membrane
Matrix:
- space within the inner membrane
- contains enzymes of Krebs and fatty acid cycles
- contains DNA, RNA, ribosomes and calcium granules

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8
Q

Discuss the function of mitochondria.

A
  • ATP production
  • store capsases which are responsible for triggering apoptosis (cytochrome C)
  • transiently store calcium to contribute to calcium homeostasis
  • abundant in the ovum for development and possibly in sperm for motility
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9
Q

Describe the structure and function of the endoplasmic reticulum.

A 
Structure: 
	- continuous with nuclear membrane 
	- system of flattened sacs (cisternae)
Function: 
	- synthesis
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10
Q

Describe the structure and function of rough endoplasmic reticulum.

A

Structure:
- ribosomes attached to cytoplasmic surface
Function:
- takes developing proteins from cytosol and continues their development
- post-translational modifications
- proteins destined for ECM e.g. mucous and enzymes
- proteins associated with the cell membrane e.g. receptors and channels
- proteins for membrane bound vesicles e.g. enzymes of lysosomes
- protein folding
- abundant in plasma cells for production of immunoglobulins

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11
Q

Describe the structure and function of smooth endoplasmic reticulum.

A

Structure:
- does not contain ribosomes
- usually less extensive than rER except in some specialised tissues
- contains cytochrome P450 enzymes which are important in the metabolism of certain drugs and toxins e.g. alcohol an barbiturates
Function:
- synthesis of lipids, phospholipids and steroids
- calcium storage
- abundant in hepatocytes for lipid synthesis and Leydig cells for steroid hormone biosynthesis

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12
Q

What is the difference between rER and sER?

A
  • rER has ribosomes attached, sER does not
  • rER plays role in synthesis and folding of proteins
  • sER synthesises lipids, phospholipids and steroids
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13
Q

Describe the structure and function of the Golgi apparatus

A

Structure:
- 5-8 folds called cisternae
- Cis-Golgi network faces the nucleus, forms a connection with ER and is the entry point to the Golgi
- cis/medial/trans-Golgi are the major processing areas that allow biochemical modifications
- trans-Golgi network is the exit point for vesicles budding off from Golgi surface (packaging and sorting)
Function:
- modifies proteins and lipids that it receives from ER

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14
Q

What is the address label for proteins bound for the lysosome?

A

Mannose-6-phosphate

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15
Q

What are lysosomes?

A
  • vesicles containing hydrolytic enzymes
  • have a low pH
  • degrade defective/old organelles, macromolecules and particles taken in from outside the cell
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16
Q

What are endosomes?

A
  • Hint - endo meaning in*

- vesicles involved in transport of molecules from plasma membrane to lysosome

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17
Q

What are peroxisomes?

A
  • a compartment for enzymes involved in oxidative reactions

- also involved in the the biosynthesis of bile acids, fatty acid metabolism and detoxification

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18
Q

Discuss Tay-Sach’s disease.

A
  • build of lipid in neuronal bodies and processes
  • because of failure to degrade lipids
  • causes neurological regression, seizures and blindness
  • rare and usually fatal
  • genetic
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19
Q

What are the functions of the cytoskeleton?

A
  • to organise cell structure and maintain the correct shape of the cell
  • to support fragile plasma membrane
  • provide mechanical linkages to allow cell/tissue to bear stress
  • allows cell to adopt specific behaviours (e.g. growth, division, migration, motility)
20
Q

What types of filament are found in the cytoskeleton?

A 
Microtubules:
	- composed of tubulin monomers
Microfilaments: 
	- composed of actin
Intermediate filaments: 
	- can be made up of keratin, vimentin, desmin and lamins
21
Q

What are the motor proteins for Microtubules and microfilaments?

A

Microtubules - powered by dynein and kinesin

Microfilaments/action - powered by myosin

22
Q

What forms the basis of cell projections? Give examples.

A

Actin Microfilaments
E.g. microvilli which increase SA for absorption in the gut
E.g. stereocilia that detect sound in the inner ear

23
Q

Which filament forms a cortical network in the cytoplasm? What does it facilitate?

A
  • actin
  • cell contraction
  • shape change
24
Q

What filaments help to produce membrane extensions such as lamellipodia and filopodia?

A
  • actin

- helps with cell motility

25
Q

What role do actin filaments play in cytokinesis?

A

Contractile ring formed at the cleavage furrow to separate dividing cells

26
Q

Where are intermediate filaments likely to be found?

A

In cells that require strength e.g. epithelial cells:

- keratin in keratinocytes of epidermis
- vimentin in fibroblasts of the dermis
- lamins in the nuclear lamina
27
Q

Discuss the structure and function of microtubules.

A

Structure:
- highly dynamic
- cylindrical tubes
- continually grow and shrink so push and pull associated structures
- organising centre is the centrosome which initiates microtubule growth towards periphery
Functions:
- mitotic/meiotic chromosomal movement
- intracellular vesicle/organelle transport
- ciliary and flagellar motility

28
Q

Describe the movements of kinesins and dyneins.

A

Kinesins move cargo AWAY from the centrosome.

Dyneins move cargo TOWARDS the centrosome.

29
Q

What is an axoneme?

A
  • Cytoskeleton component of cilia and flagella

- A structure composed of microtubules and dynein that allows for bending (role in movement)

30
Q

Where are cilia found?

A
  • In the respiratory tract where they help to move mucus and entrapped dust and microbes away from the lungs
  • Fallopian tubes where they assist the movement of the ovum towards the uterus
31
Q

What type of cell uses a flagella for propulsion?

A

Sperm cell

32
Q

Discuss Kartagener’s syndrome.

A
  • associated with defects in cilia and flagella
  • due to mutations in dynein protein
  • can cause recurrent respiratory infections as cilia cannot sweep mucus away from lungs
  • can cause infertility in males as sperm are immotile
33
Q

What type of filaments are found in the mitotic spindle?

A

Microtubules

34
Q

What are cellular junctions?

A
  • transmembrane protein complexes
  • connect the plasma membrane to adjacent cells, basement membrane and cytoskeleton
  • three types: anchoring, occluding/tight, communication/GAP
35
Q

Discuss the function and types of anchoring junctions.

A 
Function: 
	- provide mechanical stability to groups of epithelial cells so they can function cooperatively 
Types: 
	- adherens
	- desmosomes
	- focal adhesions 
	- hemidesmosomes
36
Q

What junctions do the actin filaments of the cytoskeleton interact with?

A
  • adherens (cell-cell)

- focal adhesions (cell-ECM)

37
Q

What junctions do intermediate filaments interact with?

A
  • desmosomes (cell-cell)

- hemidesmosomes (cell-ECM)

38
Q

Discuss epidermolysis bullosa simplex.

A
  • occurs due to defective intermediate filaments (hemidesmosomes)
  • disrupts dermal-epidermal later to result in severe blistering
39
Q

Discuss the structure and function of tight junctions.

A

Function:
1. Create a seal to prevent diffusion of molecules between adjacent cells
2. Create a barrier within epithelial cell membranes to prevent mixing of membrane proteins, creating apical and basolateral membranes e.g. blood brain barrier, blood-retinal barrier
Structure:
- cell-cell contact
- connects to actin cytoskeleton

40
Q

Discuss the structure and function of GAP junctions.

A

Structure:
- cell-cell
- composed of hexameters of connexins
Function:
- present in most cells
- intercellular channels which connect the cytoplasms of adjacent cells
- permit passage of inorganic ions and other small molecules
- found in large numbers during embryogenesis
- also important in cardiac and smooth muscle where they pass signals involved in contraction

41
Q

What condition can arise from a mutation in connexin-26?

A
  • inherited human deafness
  • Vohwinkel’s syndrome
    • disorder of the skin resulting in thick, honeycomb like callouses and a build up of abnormal fibrous tissue
42
Q

Discuss the important of cell junctions in the skin.

A

Adherens junctions: hold epithelial cells together
Desmosomes: provide strength for epidermal keratinocytes (integrity of epidermis)
Tight junctions: provide a seal in stratum granulosum, prevent fluid from passing across an epithelial sheet
Hemidesmosomes: hold dermis to epidermis at dermo-epidermal junction
Gap junctions: allow for passage of small molecules between cells

43
Q

What type of immune cell has an extensive rER and why?

A

Plasma cells, because they produce immunoglobulins (antibodies) which are made up of proteins.

44
Q

Describe the structure and function of free ribosomes.

A

Structure:
- made from rRNA
Function:
- mostly produce proteins for use within the cell

45
Q

List some consequences of defective organelles/structures within a cell.

A

Mitochondria: mitochondrial cytopathies (defects in oxidative phosphorylation)
Lysosomes: Tay-Sach’s disease
Microtubules: Kartagener’s syndrome
Gap junctions: Cx26 mutation causes deafness and Vohwinkels syndrome
Hemidesmosomes (intermediate filaments): epidermolysis bullosa simplex

Phase 1 - Week 1 (8 decks)

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