Eukaryotic Cells

Question 1

What is the Nucleus? What are the functions?

Answer 1

The nucleus contains the organism’s hereditary material and controls the cell’s activities.

Around 10-20um in diameter.

Question 2

What are the functions of the Mitochondria?

Answer 2

• Site of aerobic stages of respiration
• Production of energy carrier molecule ATP from respiratory substrates such as glucose

Appearance: Mitochondria are usually rod shaped and 1-10um in length.

Question 3

Chromosomes

Answer 3

Consist of protein-bound, linear DNA

Question 4

What is the cell wall? What are the functions?

Answer 4

Cell wall consists of microfibrils of the polysaccharide cellulose, embedded in a matrix. Cellulose microfibrils have considerable strength and so contribute to the overall strength of the cell wall.

Features:

• consist number of polysaccharides, eg cellulose
• There is a thin layer, called the middle lamella, which marks the boundary between adjacent cell walls and cements adjacent cells together.

Question 5

Nucleolus

Answer 5

Small spherical region within the nucleoplasm.

Manufactures rRNA and assembles ribosomes.

There may be more than 1 nucleolus in 1 nucleus.

Question 6

What are lysosomes? How are they formed?

Answer 6

Lysosomes are formed when the vesicles produced by the Golgi apparatus contain enzymes such as proteases and lipases.

They also contain lysozymes, enzymes that hydrolyse the cell walls of certain bacteria.

As many as 50 such enzymes may be contained in a single lysosome.

Up to 1um in diameter, lysosomes isolate these enzymes from the rest of the cell before releasing them, either to the outside or into a phagocytic vesicle within the cell.

Question 7

What are the cell walls of algae and fungi made of?

Answer 7

Algae : made of either cellulose or glycoproteins, or a mixture of both

Fungi: do not contain cellulose but comprise a mixture of a nitrogen containing polysaccharide called chitin, a polysaccharide called glycan and glycoproteins.

Question 8

What is the Golgi apparatus?

Answer 8

Occurs in almost all eukaryotic cells, similar to SER in structure except more compact.

Consists of stack of membranes that make up flattened sacs called cisternae, with small rounded hollow structures called vesicles.

Question 9

Smooth Endoplasmic Reticulum

Answer 9

SER lacks ribosomes on its surface and is often more tubular in appearance.

Functions:

• synthesise, store and transport lipids
• Synthesise, store and transport carbohydrates.

Question 10

What is known as the ultra structure of the cell?

Answer 10

Cells are often adapted to perform a particular function. Depending on that function, each cell type has an internal structure that suits it for its job. This is known as the ultrastructure.

Question 11

What are ribosomes? What are the 2 types?

Answer 11

Ribosomes are small cytoplasmic granules found in all cells. They may occur in the cytoplasm or be associated with the RER.

Two types:

80S - found in eukaryotic cells, around 24nm in diameter

70s - found in prokaryotic cells, mitochondria and chloroplasts, slightly smaller.

Ribosomes have two subunits - one large and one small, each contains rRNA and protein.

Despite their small size, they occur in vast numbers that they can account for up to 25% of the dry mass of a cell. Ribosomes are the site of protein synthesis.

Question 12

What are the functions of the nucleus? (3)

Answer 12

• Act as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis.
• Retain the genetic material of the cell in the form of DNA and chromosomes.
• Manufacture rRNA and ribosomes.

Question 13

What are the functions of the nucleus? (3)

Answer 13

• Act as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis.
• Retain the genetic material of the cell in the form of DNA and chromosomes.
• Manufacture rRNA and ribosomes.

Question 14

What is the Stroma? (Chloroplast)

Answer 14

Stroma is the fluid filled matrix where the second stage of photosynthesis (synthesis of sugars) takes place.

Within the stroma are other structures eg starch grains.

Question 15

What is the chloroplast envelope? (Chloroplasts)

Answer 15

Double plasma membrane that surrounds the organelle.

It’s highly selective in what it allows to enter and leave the chloroplast.

Question 16

What is the Endoplasmic reticulum? What are the two types?

Answer 16

ER is an elaborate, 3D system of sheet like membranes, spreading through the cytoplasm of the cells.

It is continuous with the outer nuclear membrane. The membranes enclose a network of tubules and flattened sacs called cisternae.

• Smooth ER
• Rough ER

Question 17

What are the functions of the Golgi apparatus?

Answer 17

• add carbohydrates to proteins to form glycoproteins
• Produce secretory enzymes eg those secreted by the pancreas
• Secrete carbohydrates eg those used in making cell walls in plants
• Transport, modify and store lipids
• Form lysosomes

The Golgi apparatus is especially well developed in secretory cells, eg epithelial cells.

Question 18

What are the functions of a cellulose cell wall?

Answer 18

Functions of the cellulose cell wall are:

• provide mechanical strength in order to prevent the cell bursting under the pressure created by the osmotic entry of water
• To give mechanical strength to the plant as a whole
• To allow water to pass along it and contribute to the movement of water through the plant

Question 19

What are grana? (Chloroplasts)

Answer 19

Grana are stacks of up to 100 disc-like structures called thylakoids.

Within the layer of thylakoids is the photosynthetic pigment called chlorophyll.

Some thylakoids have tubular extensions that join up with thylakoids in adjacent grana.

The grana are where the first stage of photosynthesis (light absorption) takes place.

Question 20

What does the double membrane of the mitochondria do?

Answer 20

Controls the entry and exit of material. It is around the mitochondria.

The inner of the two membranes is folded to form extensions known as cristae.

Question 21

What is the cristae? (Mitochondria)

Answer 21

Extensions of the inner membrane. In some species this extends across the whole width of the mitochondria.

Cristae provide a large surface areas for the attachment of enzymes and other proteins involved in respiration.

Question 22

What is the cristae? (Mitochondria)

Answer 22

Extensions of the inner membrane. In some species this extends across the whole width of the mitochondria.

Cristae provide a large surface areas for the attachment of enzymes and other proteins involved in respiration.

Question 23

Nucleoplasm

Answer 23

Granular, jelly like material that makes up the bulk of the nucleus.

Question 24

What are chloroplasts?

Answer 24

The organelles that carry out photosynthesis. Vary in shape and size but typically disc-shaped, 2-10um long and 1um in diameter.

Question 25

Rough Endoplasmic Reticulum

Answer 25

RER has ribosomes present on the outer surface of the membranes. Functions: - Provide large SA for the synthesis of proteins and glycoproteins. - Provide a pathway for the transport of materials, especially proteins throughout the cell.

Question 26

What makes eukaryotic cells different from prokaryotic cells?

Answer 26

Eukaryotic cells has a distinct nucleus and possesses membrane bound organelles

Question 27

What are the functions of lysosomes?

Answer 27

- Hydrolyse material ingested by phagocytic cells, such as WBC - release enzymes to the outside of the cell (exocytosis) in order to destroy material around the cell. - Digest worn out organelles so that the useful chemicals they are made of can be re-used - Completely break down cells after they have died (autolysis)

Question 28

Nuclear pores

Answer 28

Allow the passage of large molecules, eg mRNA, out of the nucleus. Typically around 3000 pores in each nucleus. 40-100nm in diameter.

Question 29

How are chloroplasts adapted to their function?

Answer 29

Granal membranes provide a large surface area for the attachment of chlorophyll, electron carriers and enzymes that carry out the first stage of photosynthesis in a very strict order. Fluid of the stroma possesses all the enzymes needed to make sugars in the second stage of photosynthesis. Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for photosynthesis.

Question 30

What are vacuoles?

Answer 30

A fluid filled sac bound by a single membrane. Within mature plant cells there is usually one large central vacuole. The single membrane around it is called the tonoplast. A plant vacuole contains a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments such as anthocyanins. Functions: Support herbaceous plants, and herbaceous parts of woody plants by making cells turgid. Sugars and amino acids may act as a temporary food store. Pigments may colour petals to attract pollinating insects.

Question 31

Nuclear Envelope

Answer 31

A double membrane that surrounds the nucleus. Its outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on the surface. Controls entry and exit of materials in and out of the nucleus. Contains the reactions taking place within it.

Question 32

What does the Golgi apparatus do?

Answer 32

- Proteins and lipids produced by the ER are passed through the GA in a strict sequence. - modifies these proteins often adding non-protein components, such as carbohydrates to them. - labels them allowing to be accurately sorted and sent to their correct destinations. - Once sorted, the modified proteins and lipids are transported in the Golgi vesicles which are regularly pinched off from the the ends of the Golgi cisternae. - These vesicles may move to the cell surface, where they fuse with the membrane and release their contents to the outside.

Question 33

What is the matrix? (Mitochondria)

Answer 33

The matrix makes up the remained of the mitochondrian. Contains proteins, lipids, ribosomes and DNA that allows the mitochondria to control the production of some of their own proteins. Many enzymes involved in respiration are found in the matrix.