Ch. 2.4 : Eukaryotic Cell Structure

Question 1

What is a prokaryotic cell?

Answer 1

Single - celled organism with a simple structure of just a single undivided internal area called the cytoplasm ( composed of cytosol, which is made of water, salts and organic molecules ).

Question 2

What is a eukaryotic cell?

Answer 2

They have a complicated internal structure, containing a membrane - bound nucleus ( nucleoplasm ) and cytoplasm , which contains many membrane - bound cellular components.

Eukaryotic cells make up multicellular organisms like animals, plants and fungi.

Question 3

What is metabolism?

Answer 3

It involves both the synthesis ( building up) and the breaking down the molecules.

Question 4

Describe what membranes are and what they do.

Answer 4

• selectively permeable
• control the movement of substances into and out of the cell and organelles
• effective barriers in controlling which substances enter and exit cells but are fragile

Question 5

What is the function of the nucleus?

Answer 5

• contains coded genetic information in the form of DNA molecules. DNA directs the synthesis of all protein required by the cell.
• The DNA controls the metabolic activities of the cell, as many of these proteins are the enzymes necessary for metabolism to take place.

Question 6

Describe the function of the nuclear envelope and nuclear pores

Answer 6

DNA is contained within a double membrane called a nuclear envelope to protect it from damage in the cytoplasm.

The nuclear envelope contains nuclear pores that allow molecules to move into and out of the nucleus.

Question 7

How does DNA leave the nucleus?

Answer 7

It is too large to leave the nucleus to the site of protein synthesis in the cell cytoplasm. Instead it is transcribed into smaller RNA molecules , which are exported via the nuclear pores.

Question 8

Describe how histones, chromatin and chromosomes link together

Answer 8

DNA associates with proteins called histones to form a complex called chromatin. Chromatin coils and condenses to form structures known as chromosomes.

Question 9

Describe the nucleolus

Answer 9

• an area within the nucleus which is responsible for producing ribosomes
• composed of proteins and RNA
• RNA is used to produce ribosomal RNA which is then combined with proteins to form the ribosomes necessary for protein synthesis

Question 10

Describe the function of the mitochondrion

Answer 10

Mitochondria are the site of the final stages of cellular respiration, where the energy stored in the bonds of complex, organic molecules is made available for the cell to use by the production of ATP.

They can produce their own enzymes and reproduce themselves.

Question 11

Describe the structure of mitochondria

Answer 11

• They have a double membrane.
• Inner membrane : highly folded to form structures called cristae and the fluid and the fluid interior is called the matrix.
• The membrane forming the Cristal contains the enzymes used in aerobic respiration.
• it also contains a small amount of DNA called mitochondrial (mt) DNA

Question 12

What are vesicles ? Structure and function?

Answer 12

• membranous sacs
• storage and transport roles
• consist simply of a single membrane with fluid inside
• used to transport materials inside the cell

Question 13

What are lysosomes?

Answer 13

• specialised forms of vesicles that have hydrologic enzymes
• break down waste material in cells, including old organelles
• important role in the immune system as they break down pathogens ingested by phagocytise cells
• important role in programmed cell death or apoptosis

Question 14

What is the cytoskeleton ?

Answer 14

A network of fibres necessary for the shape and stability of a cell. Organelles are held in place by its and it controls cell movement and the movement of organelles within cells.

Question 15

What are the three components of the cytoskeleton ?

Answer 15

Microfilaments
Microtubules
Intermediate fibres

Question 16

What do the microfilaments do in the cytoskeleton? What are they?

Answer 16

• contractile fibres formed by the protein actin
  Responsible for :
• cell movement
• cell contraction during cytokinesis
  ( Cytokinesis is when the cytoplasm of a single eukaryotic cell is divided into two daughter cells)

Question 17

What do the microtubules do in the cytoskeleton? What are they?

Answer 17

Globular tubular proteins polymerise to form tubes that are used to form a scaffold - like structure that determines the shape of a cell.

They also act as tracks for the movement of organelles, including vehicles, around the cell. Spindle fibre, which have a role in the physical segregation of chromosomes in cell division, are composed of microtubules.

Question 18

What do intermediate fibres do in the cytoskeleton?

Answer 18

These fibres give mechanical strength to cells and help maintain their integrity

Question 19

Where are centrioles found? What are they made of? What do they do?

Answer 19

In the cytoskeleton of most eukaryotic cells apart from flowering plants and most fungi.

Composed of microtubules.

In organisms with flagella and cilia they are thought to be involved in the positioning of these structures.

Question 20

What are centrosomes? How are they made?

Answer 20

Made from two associated centrioles.

It is involved in the assembly and organisation of spindle fibres during cell division.

Question 21

What is the function of the flagella?

Answer 21

• primarily enables cells motility

- in some cells : sensory organelle , detects chemical changes in cells environment

Question 22

Describe what stationary and mobile cilia do

Answer 22

Stationary :

• present on the surface of many cells
• important in sensory organs e.g. Nose

Mobile :
- beat in a rhythmic manner, creating a current, causing fluids / objects to move e.g. in trachea, move mucus away from lungs

Question 23

How is the cilia able to move?

Answer 23

• contains two central microtubules surrounded by nine pairs of microtubules
• this is called the 9+2 arrangement
• pairs of parallel microtubules slide over each other causing the cilia to move in a beating motion

Question 24

What organelles are involved in protein synthesis and secretion?

Answer 24

Ribosomes
Endoplasmic reticulum
Golgi apparatus
The cytoskeleton

Question 25

Describe the structure of the endoplasmic reticulum. What are the two types? What is the function of each?

Answer 25

It is a network of membranes enclosing flattened sacs called cisternae. It is connected to the outer membrane of the nucleus.

Smooth ER: responsible for lipid and carbohydrate synthesis, and storage

Rough ER : ribosomes bound to the surface. Responsible for synthesis and transport of proteins

Question 26

Ribosomes : where are they found, what is their structure, what is their function?

Answer 26

Found : cytoplasm or attached to ER. Mitochondria and chloroplasts also contain them. Found in prokaryotes too.

Structure : not membrane bound. Constructed of RNA molecules made in the nucleolus of the cell

Function : site of protein synthesis

Question 27

What is the structure of the Golgi apparatus? Role?

Answer 27

• compact structure formed of cisternae. Doesn’t contain ribosomes
• modifies proteins and packages them into vesicles ( secretory vesicles or lysosomes)

Question 28

What is the difference between secretory vesicles and lysosomes ?

Answer 28

Secretory vesicles = leave the cell

Lysosomes = stay in the cell

Question 29

Describe how organelles in a cell help synthesise proteins

Answer 29

1. Proteins are synthesised on the ribosomes bound to the endoplasmic reticulum.
2. They then pass into its cisternae and are packaged into transport vesicles.
3. Vesicles containing the proteins move towards the Golgi apparatus via the transport function of the cytoskeleton.
4. The vesicles fuse with the cis face of the GA and the proteins enter. The proteins are structurally modified before leaving the GA in vesicles from its trans face.
5. Secretory vesicles move towards and fuse with the cell-surface membrane, releasing their contents ( proteins ) by exocytosis. Some vesicles form lysosomes - these contain enzymes to be used in the cell.