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Medicine Year 1 Semester 1 > Cells And Organelles > Flashcards

Cells And Organelles Flashcards

1
Q

What is the average size of a plant/animal cell ?

A

Between 10-100 micrometers, when viewed through a Light Microscope.

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2
Q

Which is bigger plant cell or bacteria ?

A

Plant cell

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3
Q

What do eukaryotic cells lack ?

A

Cell wall

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4
Q

What is an example of a prokaryotic cell ?

A

Bacteria

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5
Q

What do prokaryotic cells lack ?

A

Nucleus, membrane bound organelles (e.g. mitochondria)

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6
Q

How much bigger is a eukaryotic cell compared to a prokaryotic cell ?

A

10 times bigger and more complex

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7
Q

What structures can be found in a eukaryotic cell ?

A

Cell membrane
Cytoplasm
Mitochondria
Ribosomes
Lysosomes
Golgi Apparatus
Endoplasmic Reticulum
Nucleus (with a nucleolus and chromatin)
Vacuoles

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8
Q

Function of the nucleus

A

DNA is packaged in the nucleus
DNA is transcribed to produce mRNA (via transcription)

Nucleus is enclosed by the double membrane, nuclear envelope.

mRNA passes from nucleus to cytoplasm via the nuclear pores.
mRNA is decoded and proteins are made (via translation) on the ribosomes

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9
Q

Chromatin

A

DNA is packaged with proteins called histones, forming a complex called chromatin.

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10
Q

2 types of chromatin

A

Euchromatin
Heterochromatin

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11
Q

Most active form of chromatin

A

Euchromatin

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12
Q

Function of nucleolus

A

Assembles newly made ribosomes

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13
Q

Function of ribosomes

A

Protein making factories of the cell.

Decode mRNA and convert it into proteins in translation.
Note: many ribosomes remain ‘free’ during translation.

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14
Q

Function of endoplasmic reticulum

A

The endoplasmic reticulum forms a network of membrane tubules continuous with the nuclear membrane.

It is the protein manufacturing plant of the cell.

Note : the ‘free’ ribosomes translate proteins destined for the cytosol, nucleus and mitochondria

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15
Q

Function of the Golgi apparatus

A

The Golgi apparatus is a series of flattened membrane proteins.

It is known as the shipping/ sorting centre of the cell.

It sorts and packages ‘cargo‘ into distinct vesicles for export to other organelles.

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16
Q

Function of the lysosomes

A

Lysosomes are membrane bound organelles containing a variety of hydrolases that digest, proteins, lipids, nucleic acid and carbohydrates.

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17
Q

Function of the vesicles

A

They transport materials between membrane compartments.

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18
Q

Function of the mitcohondria

A

The power station of the cell.

They have an outer membrane and an inner membrane.
They contain their own DNA and so replicate by dividing into 2.

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19
Q

Where does protein synthesis start ?

A

The cytosol

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20
Q

Synthesis of proteins

A

Lipids and proteins are synthesised in the endoplasmic reticulum.

Lipids are synthesised in the smooth endoplasmic reticulum and are inserted into its membrane.

The synthesis of all proteins begins in the cytosol.

The synthesis of cytosolic ribosomes is completed here and these proteins remain in the cytosol.

Transmembrane proteins carry a signal sequence which halts translation and directs the ribosomes synthesising the protein to dock with ER, forming RER.

Translation continues after docking and the protein is inserted into the membrane of the ER.

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21
Q

Movement of proteins between membranes

A

Once the proteins are in the ER, they are transported by vesicles that bud off the ER and fuse with the Golgi apparatus.

As the proteins move through the Golgi apparatus, they undergo post-translational modifications.

Vesicles that leave the Golgi apparatus, take proteins to the plasma membrane and lysosomes.

Vesicles move along microtubules to other membranes and fuse with them within the cell.

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22
Q

The secretory pathway

A

Secreted proteins are translated in ribosomes on the ER, and enter its lumen.

These proteins move through the Golgi apparatus and ate then packaged into secretory vesicles.

These vesicles move to and fuse with the plasma membrane, releasing proteins out of the cell.

Many secreted proteins are synthesised into inactive precursors and require proteolytic cleavage to produce active proteins.

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23
Q

How do vesicles move ?

A

The transport vesicles are pulled by various motor proteins (e.g. kinesin and dynein ), along the microtubules.

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24
Q

What is endocytosis ?

A

Involves engulfing extracellular material

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25
3 types of endocytosis
Phagocytosis (large particles) Pinocytosis (small molecules) Receptor mediated endocytosis
26
Phagocytosis
Involves engulfing and destroying pathogens. 1. Binding of pathogen to surface receptors 2. The plasma membrane begins engulfing the pathogen 3. This forms a phagosome 4. The phagosome fuses with the lysosome 5. Forming a phagolysosome 6. Enzymes in lysosomes destroy bacteria 7. Lysosome expels the leftovers out into the extracellular face
27
Pinocytosis
1. Solutes bind to the cell membrane 2. Cell Membrane invaginates (folds inwards) 3. This forms a vesicle (PINOSOME) 4. Motor proteins carry the vesicle using ATP deeper into the cytosol 5. The vesicle releases extracellular fluid and solutes into the cytosol
28
Receptor-mediated endocytosis (Clathrin proteins)
Note : the surface of the cell membrane have pits which are clathrin coated 1. Ligand binds to receptor 2. The edges of the pit start coming together 3. The clathrin proteins ‘link up’ 4. The vesicle pinches off and the clathrin proteins detach and move back to the cell membrane 5. The vesicle merges with an organelle called an endosome 6. The endosome uses ATP to generate a low pH which separates the ligand from the receptor 7. The vesicle splits into 2, one with all the ligands and one with the receptors Note : Vesicle 1 releases the receptors back to the surface of the cell membrane Vesicle 2 goes to the lysosome for digestion
29
Exocytosis
The Golgi apparatus packages proteins, lipids and hormones into vesicles. These vesicles can be zip lined around the cell using the cytoskeleton. The secretory vesicles move these molecules out of the cell, with the hep of motor proteins. The motor proteins pick up the vesicle and carry it towards the cell membrane along the microtubules using ATP as fuel. The vesicle moves towards the cell surface, fuses with the cell membrane and ruptures on its external side, spilling its contents into the extracellular face.
30
What is the cell membrane composed of ?
Phospholipid bilayer Cholesterol Embedded proteins
31
What are the phospholipid heads ?
Hydrophilic (POLAR)
32
What are the phospholipid tails ?
Hydrophobic (NON-POLAR)
33
Function of cholesterol
Maintains fluidity
34
What if the function of the cell membrane’s selective permeability ?
It regulates what comes in and out of the cell. It is semipermeable based on size, polarity and charge.
35
What happens to the cell membrane at LOW temperatures, without cholesterol ?
The phospholipids pack tightly together, making the cell membrane brittle and less fluid.
36
What happens to the cell membrane, at HIGH temperatures, without cholesterol ?
The phospholipids separate from one another, making the cell membrane leaky and weak.
37
What holds cells together ?
Adherens junctions
38
What are the types of cell-cell junctions found in non-mobile cells ?
Tight junctions Adherens junctions Gap Junctions
39
What are the main components of Adherens junctions ?
Actin filaments Protein plaques Cadherins
40
Function of tight junctions
Prevent water, small proteins and bacteria from passing in between
41
Function of Gap Juctions
Allow cells to communicate with each other, by allowing signal molecules to pass through.
42
What is the cytoskeleton ?
A network of proteins within the cell. It gives each cell its shape and anchors the organelles in place.
43
What is the cytoskeleton made up of ?
Actin filaments Microtubules Intermediate filaments
44
Function of Actin filaments
Slide closer together and further apart, allowing the cell to change shape during muscle contraction. Made up of 2 strands of actin in a long twisted chain.
45
Function of myosin
Enables actin to slide further apart and closer together during muscle contraction. They bind to actin filaments.
46
Function of microtubules
Made of alternating alpha and beta tubulins. Help with cell movement.
47
Function of intermediate filaments
Fasten various organelles in place within the cell. Help anchor cells to neighbouring cells through cell-cell junctions
48
Actin vs Intermediate filaments
Intermediate filaments are less dynamic than actin and microtubules, and so degenerate slowly and last longer within the cell.
49
What are prokaryotes ?
Simple, single celled organisms, without a nucleus or membrane bound organelles Spherical rod shaped simple cell division Circular DNA not enclosed by a membrane
50
What are eukaryotes ?
Multicellular organisms Mitosis/ meiosis Linear DNA enclosed by a nuclear envelope
51
Nuclear envelope
Layer of 2 membranes that surrounds the nucleus of a cell
52
Nuclear pores
Selective aqueous channels in the nuclear envelope that allow materials (mRNA) to move between the nucleus and the cytosol.
53
Protein Expression
DNA --- Transcription --- mRNA --- Translation by ribosomes --- protein
54
Which protein packages DNA in eukaryotes ?
Histones form chromatin complexes
55
Nucleolus
Ribosome production
56
Function of RER
Site of membrane synthesis Modifies protein Quality control Signals stress
57
Brief overview of Secretory Pathway
Vesicles carry cargo from RER to Golgi Golgi sorts, modifies and processes packages Some vesicles fuse with PM and release proteins out of cell Some vesicles contain secretory proteins
58
Kinesin
Pushes vesicles away from organelle
59
Dyenin
Pulls vesicles back to organelle
60
What are the 2 great steps in eukaryote cell evolution ?
Compartmentalisation Mitochondria
61
Compartmentalisation
Internal membrane compartments with a range of specialised functions allowing reactions can be SEPARATED, concentrated and optimised.
62
Mitochondria
powerhouse of the cell site of ATP production
63
How did mitochondria evolve ?
Large non-nucleated cell engulfed a bacterium which provides ATP for growth. Cell membrane invaginated and formed internal membranes ER synthesises proteins and coats nucleoid to form nuclear envelope.
64
Cell cycle
Well regulated events resulting in the duplication of DNA and cell division.
65
Mitosis
Cell division of somatic cells produces 2 diploid daughter cells with no genetic variation.
66
Main purpose of mitosis
Proliferation
67
Meiosis
Cell division of germ cells, produces 4 haploid daughter cells with an increased level of genetic variation.
68
Main purpose of meiosis
sexual reproduction
69
5 Stages of Mitosis
Interphase Prophase Metaphase Anaphase Telophase
70
3 causes of familial hypercholesterolemia
1. LDLR is not properly transported from RER to Golgi to be expressed on cell surface. 2. LDLR bound to LDL does not cluster in endocytic vesicles on plasma membranes. 3. LDLR is not recycled back to the cell surface.

Medicine Year 1 Semester 1 (37 decks)

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