Eukaryotic Cell Ultrastructure

Question 1

What are the 3 structural components of the cytoskeleton?

Answer 1

• Microfilaments
• Microtubules
• Intermediate Fibres

Question 2

What are the functions of the Cytoskeleton?

Answer 2

• Supporting / stabilising the whole cell
• Maintains cell shape
• Allows movement of cilia / flagella
• Allows for cell shape to change (e.g. cytokinesis, phagocytosis)
• Movement of chromosomes
• Movement of vesicles along microtubules

Question 3

What are microfilaments and what is their function?

Answer 3

Microfilaments are fibres made from the protein Actin. They are responsible for moving the cell & cytoplasm in cytokinesis.

Question 4

What are microtubules and what is their function?

Answer 4

They are formed of the globular protein Tubulin and polymerise to from tubes that determine the cell’s shape. They also act as tracks for organelles moving around the cell.

Question 5

What are intermediate fibres and what is their function?

Answer 5

They are fibres which give strength to cells and helps maintain their integrity.

Question 6

What are the components of the Nucleus?

Answer 6

• Nuclear Envelope (a double membrane)
• Nuclear pores
• Nucleolus
• Chromatin

Question 7

What is the double Nuclear envelope?

Answer 7

A double membrane which encompasses the nucleus and prevents damage. It protects the DNA.

Question 8

What is the function of nuclear pores?

Answer 8

They allow for small molecules to enter and leave the nucleus (e.g. nucleotides enter for DNA replication and mRNA leaves).

Question 9

What is the function of the nucleolus?

Answer 9

The nucleolus is composed of RNA and proteins and is the site of ribosome production.

Question 10

What is the Chromatin?

Answer 10

A complex composed of DNA and associated histone proteins. Chromatin coils and condenses to form chromosomes. Chromatin contains the genetic code and controls the activity of the cell.

Question 11

What is the function of the nucleus?

Answer 11

• Controls all cell activity
• Where genetic code is stored, replicated and transcribed into RNA.
• The nucleus is attached to the Rough ER so that the mRNA can easily access ribosomes.

Question 12

What is the structure of the Rough Endoplasmic Reticulum?

Answer 12

Rough ER consists of stacks of membrane bound (fluid filled) sacs which form sheets called cisternae.

It is attached to the Nucleus and is covered by ribosomes. It consists of an interconnected system of flattened sacs.

Question 13

What is the function of the Rough ER?

Answer 13

It is the site of protein synthesis and transport. Some proteins will leave the cell and others will be placed on the surface of the cell membrane.

Question 14

What is the structure of the Smooth Endoplasmic Reticulum?

Answer 14

Smooth ER is a system of interconnected tubules similar to the Rough ER but without ribosomes.

Question 15

What is the function of the Smooth ER?

Answer 15

Responsible for lipid, carbohydrate and steroid synthesis and storage.

Question 16

What is the structure of ribosomes?

Answer 16

• 2 subunit organelle
• Made from RNA and protein
• Not membrane bound
• Around 22nm in diameter
• Found floating free in cytoplasm / attached to Rough ER

Question 17

What is the function of ribosomes?

Answer 17

They synthesise proteins by assembling amino acids into proteins in chains using mRNA.

Question 18

What is the structure of a mitochondrion?

Answer 18

• Oval shaped
• Surrounded by a double membrane
• Inner membrane forms structure known as Cristae - increases surface area
• Solution inside is called a matrix which contains enzymes for respiration
• Contains mitochondrial DNA, which allows mitochondrion to reproduce and create enzymes

Question 19

What do mitochondrion release?

Answer 19

ATP as a result of aerobic respiration.

Question 20

What is the structure of the Golgi Apparatus?

Answer 20

Composed of cisternae - they are continuously formed from the ER at one end and bud off into Golgi vesicles at the other end.

Question 21

What is the function of the Golgi Apparatus?

Answer 21

1. Receives proteins from the Rough ER
2. Modifies the protein by adding sugars / carbohydrate chains and folds the protein into a specific shape
3. Repackages the modified protein into a vesicle
4. Makes lysosomes
5. Synthesises lipids

Question 22

What are lysosomes?

Answer 22

Spherical sacs surrounded by a single membrane which contain hydrolytic digestive enzymes known as lysozymes.

Question 23

What is the function of lysosomes?

Answer 23

Their hydrolytic enzymes use water to break down worn out components of the cell and digest invading cells.

Question 24

What are centrioles?

Answer 24

A component of the cytoskeleton composed of many microtubules. They are small hollow tubes that appear next to the nucleus of animal cells ONLY.

Each centriole contains a ring of 9 triplet microtubules.

Question 25

What is the function of centrioles?

Answer 25

They make a copy of themselves during cell division and help form the spindle fibre.

Question 26

What are cilia?

Answer 26

‘Hair like’ extensions that protrude from some types of animal cells. They consist of an outer membrane and a 9+2 arrangement.

Question 27

What is meant by a 9+2 arrangement?

Answer 27

A ring of 9 pairs of protein microtubules with 2 microtubules in the middle.

Question 28

What is the function of cilia?

Answer 28

Locomotion. They beat to create a current which wafts fluid / mucous / objects.

Question 29

What is the structure of the flagella?

Answer 29

Similar to cilia but longer - they too have a 9+2 arrangement. They protrude from the cell and are surrounded by the plasma membrane.

Question 30

What is the function of the flagella?

Answer 30

Their whip-like shape enables a cell’s mobility to propel cells (e.g. sperm cells) forward. The microtubules contract to make the flagellum move.

Question 31

What is the plasma membrane?

Answer 31

The membrane found on the surface of animal cells and inside the cell wall of plant and prokaryotic cells.

Question 32

What is the structure of a plasma membrane?

Answer 32

A phospholipid bilayer composed of lipids and proteins.

Question 33

What is the function of the plasma membrane?

Answer 33

Regulates the movement of substances into and out of the cell.

It contains receptor molecules which allow it to respond to chemicals such as hormones.

Question 34

Describe the process by which proteins are produced and secreted (part 1).

Answer 34

• DNA in the nucleus contains the genetic code / gene needed to make proteins.
• The gene is copied by mRNA which takes it from the nucleus to the Rough ER’s ribosomes via the nuclear pores.
• The protein is synthesised on the ribosome by assembling amino acids into chains.
• The protein is passed into the Rough ER’s cisternae and packaged into a vesicle.

Question 35

Describe the process by which proteins are produced and secreted (part 2).

Answer 35

• The vesicle travels to the golgi apparatus via the microtubules and fuses with it.
• The golgi apparatus processes and structurally modifies the protein (e.g. by adding carbohydrate chains to form glycoproteins).
• The golgi repackages the protein into a secretory vesicle.
• Secretory vesicles travel along the microtubules and fuse to the cell surface membrane. The contents of the vesicle are then released by exocytosis.

Question 36

What is mRNA?

Answer 36

Messenger RNA. RNA (ribonucleic acid) is a single strand of DNA.