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Eukaryotic Cell Ultrastructure Flashcards

1
Q

Define Eukaryotic Organism

A

Single/multicellular organism that possesses a nucleus and membrane-bound organelles.

These are animals, protoctists, fungi, plants.

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2
Q

Define Nucleus

A

A double membrane-bound organelle found in eukaryotic cells that stores the genetic information of the cell as chromosomes (hereditary material) and controls/regulates the activities of the cell.

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3
Q

Describe the appearance of the nucleus

A

10-20 micrometers in diameter. Has nucleolus, chromatin, nucleoplasm, nuclear pore, nuclear envelope. Surrounded by the RER. Outer membrane is continuous with the RER so it often has ribosomes on its surface.

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4
Q

What is chromatin?

A

The material from which chromosomes are made. A complex of DNA and histone proteins. Condense into visible chromosomes during prophase.

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5
Q

What does the nucleolus do?

A

Manufactures rRNA and assembles ribosomes.

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6
Q

What is the nucleoplasm?

A

Granular, jelly-like substance that makes up the bulk of the nucleus. Essentially the cytoplasm of the nucleus.

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7
Q

What is the nuclear envelope?

A

The double membrane that controls what enters/leaves the nucleus.

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8
Q

What is a nuclear pore? How many are there in a nucleus? How big are they?

A

Hole in the nuclear envelope that allows large molecules eg mRNA to enter/leave the nucleus. 40-100 nm in diameter. Around 3000 in a nucleus.

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9
Q

Function of the nucleus

A

Control centre of a cell through the production of mRNA and tRNA and hence it regulates protein synthesis. Retains the genetic material of the cell in the form of chromosomes. Manufactures rRNA and assembles ribosomes.

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10
Q

Define ribosome

A

A ribonucleoprotein (equal amount of rRNA and proteins) found either free in the cytoplasm or associated with the RER that is the site of protein synthesis (specifically translation).

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11
Q

Size of the 80s ribosome

A

25 nm but makes up ~25% of the cells dry mass because there are so many of them.

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12
Q

What does S mean?

A

Svedberg units. This is how fast molecules move in a centrifuge.

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13
Q

Difference between 80S and a 70S ribosome

A

80S is bigger, found in eukaryotic cells and has a 60S (L) and 40S (S) subunit. 70S is smaller, found in prokaryotes and mitochondria/chloroplasts and has a 50S (L) and 30S (S) subunit.

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14
Q

Role of the small subunit

A

Binds to mRNA and decodes the genetic information.

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15
Q

Role of the large subunit

A

Site of translation. rRNA and proteins hold the amino acid-carrying tRNA molecules in place. The condensation enzymes linked to rRNA catalyse the formation of peptide bonds between amino acids, creating a polypeptide chain.

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16
Q

How does the ribosome as a whole create a polypeptide chain?

A

mRNA sits between the 2 subunits. The ribosome moves along the mRNA and translates it into a polypeptide.

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17
Q

Define mitochondrion

A

Double membrane-bound organelle found in eukaryotic cells that is the site of aerobic respiration.

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18
Q

Is the ribosome also the site of anaerobic respiration?

A

No.

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19
Q

Shape, length and role of the mitochondrion

A

Rod shaped, 1-10 micrometers in length. Responsible for the production of ATP from the energy released in the breakdown of glucose (or other suitable respiratory substrates).

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20
Q

Which cells will have bigger mitochondria/more of them and why?

A

Cells that carry out active transport eg root hair cells. Metabolically active cells eg muscle and epithelial cells. A plentiful supply of ATP is needed. These mitochondria will also have more cristae.

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21
Q

Describe the structure of the mitochondrion

A

Outer membrane, intermembrane space, inner membrane (folds to form cristae), matrix.

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22
Q

Why does the inner membrane fold to form cristae?

A

To increase the surface area for the attachment of enzymes/other proteins involved in AeR.

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23
Q

What is contained within the matrix?

A

All the lipids, proteins and enzymes needed for AeR. A circular loop of DNA and 70S ribosomes so the mitochondrion can produce some of its own proteins needed for AeR.

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24
Q

Define Chloroplast

A

Double membrane-bound organelle found in plants and algae that is the site of photosynthesis.

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25
Describe the structure of a chloroplast
Chloroplast envelope, stroma, thylakoids, granum, intergranal lamellae, starch granule, loop of DNA, 70S ribosomes, drop of lipids.
26
Thylakoid membrane structure and function
First stage of PS (light absorption) happens here. They are membrane bound. Contain chlorophyll or carotene (if autumn leaves). Organised into Grana (stacks of thylakoids – up to 100 in each stack). These increase the SA of the thylakoids for the attachment of membrane-bound chlorophyll, electron carriers and photosynthesis enzymes.
27
Intergranal lamellae function
Thin and flat thylakoid membranes that facilitate molecular trafficking and minimise packing density.
28
Stroma definition
Fluid-filled matrix where the second stage of PS (sugar synthesis) takes place.
29
What is contained within the stroma?
All the enzymes needed for sugar synthesis. Drops of lipids (a store of lipids). Starch granules (store of carbohydrates in plants). Loop of DNA and 70S ribosomes.
30
Chloroplast envelope definition
Double membrane around the chloroplast. Very selective in what it lets in and out.
31
Endoplasmic Reticulum
Series of elaborate, 3D, membrane-bound flattened sacs formed from continuous folds of membrane. Spreads through the cell’s cytoplasm. Continuous with the outer nuclear membrane.
32
What does the RER do to proteins?
Folds and processes them after they are made by the ribosomes (post-translational modifications). Checks their quality – incorrectly folded ones are rejected. Sorts the properly functioning ones for their final destinations. Adds carbs to form glycoproteins
33
How is the RER suited for its function?
Large SA so lots of ribosomes can be on the surface and so lots of proteins can be made. Outer surface is fully covered in ribosomes.
34
Smooth ER Structure and Function
Also a series of membrane-bound flattened sacs. No ribosomes on outer surface (they are not needed). More tubular appearance than the RER. Synthesises, stores and modifies lipids and carbs.
35
Golgi Apparatus Structure
Fluid-filled membrane bound flattened sac. Stack of membranes that make up the flattened sacs (cisternae). Surrounded by vesicles (small, round, hollow structures).
36
Golgi Apparatus function
Modifies and packages proteins and lipids into Golgi vesicles. Produces lysosomes.
37
Lysosome function
Function - released hydrolytic enzymes BREAKS THINGS DOWN: - Completely breaks down the contents of a cell after it has died (autolysis) - Break down worn out organelles to reuse the useful biological molecules it is made from - Release hydrolytic enzymes from the cell by exocytosis to break down matter outside of the cell
38
Give a type of cell with more prominent lysosomes and why is this the case?
- Phagocytes - to hydrolyse what is trapped in the phagosome —> phagolysosome
39
What is a Golgi vesicle?
- Membrane bound sac organelle that buds off from the Golgi apparatus - Transports packaged proteins/lipids to their final destinations, also used for storage
40
Which cells would have a more defined Golgi apparatus?
- Any secretory cells - B plasma cells - Pancreatic cells - Salivary gland cells - Goblet cells - Breast cells
41
How are proteins made in cells? Give all the organelles involved
- DNA in the nucleus is the genetic code for the protein - Mitochondria provide energy/ATP for protein synthesis - Ribosomes translate genetic code into a polypeptide - RER folds it/post-translational modifications/checks its quality/adds carbs - Golgi apparatus modifies it and packages it into a vesicle - Vesicle transports it to the CSM and fuses with it - Exocytosis at the CSM
42
How are microtubules formed?
- alpha tubulin and beta tubulin (globular proteins) join together to form a dimer - dimers (reversibly) attach head to tail to form a protofilament - 13 protofilaments join together to form a hollow, microscopic tube - this is the microtubule - it is about 25 nm in diameter
43
4 organelles where microtubules are present
Centrioles, cilia, flagella, cytoskeleton
44
Name the 2 parts of the cytoplasm
Cytoskeleton, Cytosol
45
What is the cytosol
- fluid part of the cytoplasm - semiliquid complex of water, dissolved minerals and proteins - medium for chemical reactions to occur
46
Cytoskeleton structure and function
- consists of microfilaments and microtubules - enables the cell to move - supports organelles and keeps them in position - enables transport of molecules within the cell - strengthens the cell and maintains its shape
47
What do microfilaments consist of
Thin, double stranded, intertwined strands of actin monomers twisted into a double helix
48
Microvilli structure and function
Projections off the CSM that increase the surface area of absorption cells (eg epithelial cells in the ileum)
49
Centriole structure
- Small hollow cylinder made of microtubule triplets, sits in the cells cytoplasm - Found in all animals cells and some plant cells (not fungi or flowering plants as the rigid cell wall can organise the microtubules that form spindle fibres during cell division) - 2 at right angles to each other = centrosome
50
Centriole function
- Facilitates the separation of chromosomes during cell division - Help produce cilia in non-dividing cells - Organise microtubules in the cytoplasm
51
Cilia structure
- Small hair like structures found on the CSM of animal cells ONLY - Surrounded by an outer membrane - 9 pairs of microtubules on the outside and 1 pair in the middle
52
Cilia function
- Microtubules contract, allowing the cilia to move - This movement moves substances over the outer cell surface (eg cells in the trachea)
53
Flagella structure
- Same as cilia, but much longer microtubules.
54
Flagella function
- Microtubules contract, enabling the flagella to move - This moves the whole cell (sperm cells and some bacteria cells)
55
Cell wall structure and function
- Formed outside of the CSM - Provide structural support to the cell - Peptidoglycan in bacteria, cellulose in plants and chitin in fungi - Freely permeable so doesn’t disrupt the function of the CSM
56
Large permanent vacuole structure and function
- Only found in plant cells - Surrounded by an outer membrane (Tonoplast) - Contains cell sap
57
How are cell vacuoles different in animal and plant cells?
- Animal ones are not permeable and are much smaller
58
What is the composition of the cell sap? What does it do?
- Water, mineral ions, enzymes, sugars, amino acids waste products - Pushes against the cell wall to create turgor pressure - Regulates the water potential of the cytoplasm - Collects waste products so they don’t accumulate in the cytoplasm and damage the cell
59
Why is a cell wall not needed in animal cells?
- The water potential of the liquid surrounding animal cells is tightly controlled - So animal cells are less prone to large changes in water potential - Therefore they are less likely to burst but they still will if WP gets too high - Plant cells need a CW to withstand turgor pressure
60
What are plasmodesmata?
- Microscopic channels that connect plant cells - Facilitate transport and connection between them - Consist of cytoplasm surrounded by a membrane and a central rod of endoplasmic reticulum for structural support

Biology AS (13 decks)

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