Eukaryotic cells

Question 1

How big are eukaryotic cells?

Answer 1

larger cells around >10um

Question 2

What are eukaryotic cells?

Answer 2

multicellular organisms

Question 3

Do eukaryotic cells have a nucleus and organelles

Answer 3

They have a nucleus and other membrane bound organelles

Question 4

What is the DNA like in eukaryotic cells?

Answer 4

DNA is linear and associated with proteins to form chromatin

Question 5

How big are the ribosomes in eukaryotic cells?

Answer 5

large (80S)

Question 6

Do eukaryotic cells have a cytoskeleton?

Answer 6

They always have a cytoskeleton.

Question 7

How do eukaryotic cells get their motility?

Answer 7

Motility by flexible waving cilia or flagellae (made of tubulin).

Question 8

How does cell division occur in eukaryotic cells?

Answer 8

By mitosis or meiosis

Question 9

In eukaryotic cells, is reproduction sexual or asexual?

Answer 9

It is sexual or asexual

Question 10

What metabolic pathways do eukaryotic cells have?

Answer 10

They have the common metabolic pathways.

Question 11

What is the cell membrane (plasma membrane), what is it made of and what does it do?

Answer 11

Thin flexible layer around the outside of all cells.

Made of phospholipids and proteins.

Separates the contents of the cell from the outside environment, controls what materials enter and exit the cell.

Question 12

What is the cytoplasm (cytosol), what does it contain and what happens here?

Answer 12

The solution within the cell membrane.

Contains enzymes for glycolysis (the first stage of respiration and other metabolic reactions as well as; sugars, salts, amino acids, nucleotides and everything else needed for the cell to function.

It is where the first stage of respiration (glycolysis) takes place.

Question 13

What is the nucleus?

Answer 13

The largest organelle.

Question 14

Describe the structure of the nucleus:

Answer 14

Surrounded by a nuclear envelope, has an interior called the nucleoplasm which is full of chromatin. The dark region of the nucleus is the nucleolus.

Question 15

What does the nucleus do?

Answer 15

It is involved in making ribosomes and ‘processing’ m-RNA (i.e. removing introns) (the non-coding sections of RNA transcript).

Question 16

What is the nuclear envelope?

Answer 16

A double membrane with nuclear pores - large holes containing proteins that control the exit of substances such as mRNA and ribosomes from the nucleus.

Question 17

What is chromatin?

Answer 17

A DNA/protein complex containing the genes.

Question 18

What happens to the chromatin during cell division?

Answer 18

It becomes condensed into discrete observable chromosomes.

Question 19

What are the 80S ribosomes, what are they made of and where are they?

Answer 19

Smallest, most numerous of the cell organelles and the sites of protein synthesis. All eukaryotic ribosomes are the larger 80S type.

Made of protein and RNA and manufactured in the nucleolus of the nucleus.

Can be free in the cytoplasm or (more commonly) attached to the rough endoplasmic reticulum. Often found in groups called polysomes.

Question 20

What is the endoplasmic reticulum (ER), what does it do, where is it and what 2 forms does it come in?

Answer 20

Collection of membrane channels

Form an important transport ‘highway’ within the cell allowing molecules to move from one place to another. Plays an important role in protein synthesis.

Attached to and formed from the outer membrane of the nucleus.

Comes in smooth and rough forms.

Question 21

What is the rough endoplasmic reticulum (RER) ‘made of’ and what do these do?

Answer 21

Studded with numerous 80S ribosomes giving it its rough appearance.

The ribosomes synthesise proteins processed in the SER by modifying the polypeptide chain or adding carbohydrates before being exported from the cell via the golgi body.

Question 22

What is the smooth endoplasmic reticulum (SER) ‘made of’ and what do these do?

Answer 22

Similar to the RER but without the ribosomes.

Series of membrane channels involved in the synthesis and transport of materials, mainly lipids and glycoproteins, needed by the cell.

Question 23

What is the Golgi body (or apparatus), what is its job and what happens here?

Answer 23

A series of flattened membrane vesicles formed from the endoplasmic reticulum.

Its job is to transport proteins from the RER to the cell membrane for export.

Parts of the SER containing proteins fuse with one side of the Golgi body membranes, while at the other side small vesicle bud off and move towards the cell membrane, where they fuse, releasing their contents by exocytosis.

Question 24

What are vacuoles and what do they do?

Answer 24

Membrane-bound sacs containing a dilute solution. Most cells have small vacuoles that are formed as required, but plant cells usually have one very large permanent vacuole that fills most of the cell, so that the cytoplasm (and everything else) forms a thin layer round the outside. Plant cell vacuoles are filled with cell sap, and are very important in keeping the cell turgid. Some unicellular protoctists have feeding vacuoles for digesting food, or contractile vacuoles for expelling water (osmoregulation).

Question 25

What are lysosomes and what do they do?

Answer 25

Small membrane bound vesicles containing digestive enzymes.

They are used to break down unwanted chemicals, toxins, organelles or even whole cells, so that the materials may be recycled. They can also fuse with a feeding vacuole to digest its contents. Responsible for cell death - autolysis.

Question 26

What is the cytoskeleton, where is it and what does it do?

Answer 26

A network of protein fibres extending throughout all eukaryotic cells, used for support, transport and motility. It is attached to the cell membrane and gives the cell its shape, as well as holding all the organelles in position.

There are 2 types of protein fibres (microfilaments and microtubules); each has a corresponding protein that can carry a cargo such as an organelle, chromosome or other cytoskeleton fibres along the fibre. They are responsible for chromosome movement in mitosis and the subsequent division of the cell, cytoplasmic streaming or cyclosis (in plants only), cilia and flagella movements, and muscle contraction.

Question 27

What is the centriole and what does it do?

Answer 27

A set of short microtubules (‘9+2’) involved in cell division. Before each division the centriole replicates itself and the two centrioles move to opposite ends of the cell, forming the spindle that organises and separates the chromosomes.

Question 28

What are cilia and flagellae (or undulipodia) and what do they do?

Answer 28

Long flexible ‘tails’ present in some cells and used for movement. They are surrounded by the cell membrane and are full of microtubules and motor proteins, so they are capable of complex swimming movements.

There are two types:
Flagellae - (no relation to the bacterial flagellum), are longer than the cell and there are usually one or two of them.
Cilia - though identical in structure, are much smaller and there are usually many of them.

Question 29

What are microvilli and what do they do?

Answer 29

Small finger-like extensions of the cell membrane found in some animal cells (e.g. the epithelial cells of the gut and kidney), where they increase the surface area for absorption. They are just visible under the light microscope as the brush border.

Question 30

What is the cell wall and what does it do?

Answer 30

A thick layer outside the cell membrane used to give a cell strength and rigidity. They consist of a network of fibres, which give strength but are freely permeable to solutes (unlike membranes).

Plant cell walls are made mainly of cellulose, but also contain pectin, lignin and other polysaccharides. It is built up in layers with the middle lamella separating the cell wall of adjacent cells. There are often channels through plant cell walls called plasmodesmata, which link the cytoplasm of adjacent cells.

Fungal cell walls are made of chitin.
Animal cells do not have a cell wall.

Question 31

What are semi-autonomous organelles?

Answer 31

Organelles that contain their own DNA (coding for about 50% of the organelle) and reproduce independently of the nucleus.

Question 32

What are the 2 semi-autonomous organelles?

Answer 32

Mitochondria and chloroplasts.

Question 33

What is special about mitochondrial DNA?

Answer 33

Mitochondrial DNA mutates at a known, constant rate and is only inherited from the mother, so it can be used to track purely female genetic lines. In the same way, the Y chromosome is only passed on from father to son and so can be used to track the purely male genetic line.

Question 34

What are mitochondria and what do they do?

Answer 34

Sausage shape organelles (2-5um long), where aerobic respiration takes place in eukaryotic cells. They are surrounded by a double membrane, the outer membrane is quite permeable but the inner membrane is highly folded into cristae, which give it a large surface area.

It is studded with ATPase, the enzyme which is the main site of ATP synthesis. This is where the last stage of respiration - the ETC takes place.

The space enclosed by the inner membrane is called the mitochondrial matrix and contains small circular strands Of DNA and 70S ribosomes. This is the site of the TCA or Kreb’s cycle stage of respiration.

Question 35

What are chloroplasts and what do they do?

Answer 35

They are bigger and fatter than mitochondria (so settle first when cells are homogenised and centrifuged), chloroplasts are the site of photosynthesis, so are only found in the photosynthetic cells (plants and algae).

Like mitochondria a double membrane encloses them, but they also contain membranes arranged in disks called thylakoids which contain chlorophyll and other photosynthetic pigments and carry out the light reactions of photosynthesis. The thylakoids are then stacked into piles called grana.

The space between the inner membrane and the thylakoid is called the stroma - the site of the light-independent (or ‘carbon-fixing’) stage of photosynthesis. Chloroplasts also contain starch grains, 70S ribosomes and circular DNA.