2.4 Eukaryotic Cell Structure

Question 1

What is a eukaryote?

Answer 1

Any organism consisting of one or more cells that contain DNA in a membrane-bound nucleus, separate from the cytoplasm.

Question 2

Examples of Eukaryotes

Answer 2

Animals, plants, fungi and a diverse group known as the protists (or protoctists)

Question 3

What are membranes?

Answer 3

Membranes cover the surface of every cell, and also surround most organelles within cells. (plasma or cell surface membranes).

Question 4

Functions of membranes

Answer 4

Keeping all cellular components inside the cell
Allowing selected molecules to move in and out of the cell.
Isolating organelles from the rest of the cytoplasm, allowing cellular processes to occur separately.
Important in cell signalling.
Allows a cell to change shape.

Question 5

What organelles are involved in protein synthesis?

Answer 5

The nucleus, ribosomes, endoplasmic reticulum (ER), Golgi apparatus (GA)

Question 6

Describe the nucleus

Answer 6

Consists of genetic material, chromatin, bound in a nuclear membrane.
Contains one or more denser areas called nucleoli.

Question 7

Describe ribosomes

Answer 7

Ribosomal RNA (rRNA) is transcribed in the nucleolus. This does not form a template for a protein, but fold up into sub-units that pair up to make ribosomes.

Question 8

Describe translation in protein synthesis

Answer 8

Most ribosomes attach to the rough endoplasmic reticulum (ER), where they translate mRNA into proteins. These are then transported by the flattened sacs or cisternae, of the ER.

Question 9

Describe Smooth ER in protein synthesis

Answer 9

Smooth ER has no ribosomes, but is involved in the transport of proteins
Important role in the production and storage of carbohydrates lipids and other molecules.

Question 10

Describe Transport Vesicle

Answer 10

The membrane of the ER continually buds off to form vesicles. These are packages of proteins and other molecules formed on the ER, for transport to the Golgi apparatus

Question 11

Describe Golgi apparatus

Answer 11

The Golgi apparatus modifies molecules and packages them for specific destinations inside or outside the cell.
Vesicles fuse with the cisternae at one end, and new ones bud off at the other.

Question 11

Describe mitochondria

Answer 11

It is an energy-generating organelle.
It is surrounded by two membranes. The inner layer folds inwards to form the cristae. The cristae project into a liquid called the matrix.
The inner membrane is coated in enzymes, which catalyse the reactions of aerobic respiration to produce ATP.

Question 12

Describe Golgi vesicles

Answer 12

Some Golgi vesicles are lysosomes , containing enzymes that break down old organelles or infectious bacteria.
Other transport proteins to elsewhere in the cell, or eject them by exocytosis.

Question 13

What are microtubules

Answer 13

Main component of a cell’s cytoskeleton.
They connect to cell’s organelles to each other to keep them in place (almost like a train track)
They can also alter their length to affect the shape of the cell or cause it to move.

Question 14

What are centrioles?

Answer 14

Co-ordinate the nucleation and growth of microtubules in all eukaryotes except the higher plants.
An example of a microtubule organising centre (MTOC).

Question 15

What are actin filaments?

Answer 15

A secondary element of the cytoskeleton is a network.
These are not made of microtubules, but work with them to maintain or change the cell’s shape.

Question 16

What is cilia

Answer 16

They are short (5-10um) hair-like overgrowths on the surface of the cell.
They beat to power movement (e.g. white blood cells) or move fluid across the cell’s surface (e.g. in respiratory epithelium).

Question 17

What is flagellum?

Answer 17

Flagella on eukaryotic cells are like cilia but longer, they stick out from the cell surface and are surrounded by the plasma membrane.
Inside they are like cilia too - two microtubules in the centre and nine pairs around the edge. The microtubules contract to move the flagellum