Cell Structure And Organelles

Question 1

Describe the structure and function of nucleus

Answer 1

• nuclear envelope with nuclear pores which allow small molecules like mRNA to leave nucleus and separates the nucleus from cytoplasm to protect DNA from damage
• contains DNA wrapped around histone proteins to form chromatin which hold the genetic information of cell and controls metabolic reactions of cell because many of the proteins it codes for are needed for these reactions.. chromatin then condenses into chromosome during mitosis
• nucleolus synthesises ribosomes with rRNA and proteins
• nucleoplasm contains DNA required for mitosis, semi conservative replication

Question 2

Describe the structure and function of centrosomes

Answer 2

• two centrioles perpendicular to each other form centrosomes
• composed of microtubules
• involved in production of spindle fibres during mitosis

Question 3

Where are centrosomes NOT found?

Answer 3

In flowering plants and fungi

Question 4

Describe the structure and function of mitochondria?

Answer 4

• double membrane structure
• inner membrane greatly folded to from cristae which gives a large surface area for enzymes and proteins for aerobic respiration.. electron transport chain
• fluid composed in mitochondria is called the matrix which contains its own DNA and ribosomes(meaning they can produce their own enzymes and reproduce themselves) and enzymes for aerobic respiration

Question 5

Describe the structure and function of rough ER

Answer 5

• many flattened membranes called cisternae that extend from the nuclear envelope
• contains ribosomes on cisternae which synthesise proteins
• folding and processing of proteins
• stores protein till wanted by Golgi body

Question 6

Describe the structure and function of smooth ER

Answer 6

• lipid synthesis
• carbohydrate synthesis
• storage

Question 7

Describe the structure and function of Golgi body

Answer 7

• composed of flattened membrane stacks called cisternae
• there are usually vesicles beside them
• vesicles enter cis face and leave trans face
• modification of proteins by usually adding a carbohydrate chain
• packages protein in a vesicle
• produces lysosomes
• synthesises glycoproteins

Question 8

Describe the structure and function of lysosomes

Answer 8

• fluid filled membrane surrounded sac
• contains digestive hydrolase enzymes(hydrolytic enzymes) to break down waste material like worn out organelles or invading cells like pathogens that have been ingested by phagocytes
• has H+ pump so acidic environment is maintained
• secretes digestive enzyme via exocytosis
• involved in cell apoptosis

Question 9

Describe the structure and function of ribosomes

Answer 9

• not membrane bound
• small subunit and large subunit
• mRNA attaches to small subunit for protein synthesis
• small subunit contains mRNA binding site
• site of protein synthesis
• made by nucleolus with rRNA and proteins
• contains the enzyme peptidyl transferase which catalyses the formation of peptide bonds between amino acids during translation

Question 10

Describe the structure and function of cell surface membrane

Answer 10

• selectively permeable membrane with phospholipid bilayer, many proteins embedded and also cholesterol
• controls what enters and exists the cell
• for cell signalling because glycoproteins on cell surface membrane act as receptors
• separates cell from aqueous environment

Question 11

Define an organelle

Answer 11

• membrane bound compartment so that it has specific conditions for specific reactions

Question 12

Describe the structure and function of chloroplasts?

Answer 12

• double membrane bound
• membrane bound stacks called thylakoids
• there are many membrane bound thylakoids so greater surface area for more photosynthetic pigments and electron carriers so more light can be absorbed
• many stacks= granum
• grant joined by lamellea
• fluid is called stroma where the light independent reactions happen
• starch grains

Question 13

Describe the structure and function of a vesicle

Answer 13

• one membrane bound sac that is also fluid filled

- transports substances to and from organelles or cells themselves

Question 14

State the three components of the cytoskeleton

Answer 14

• microtubules
• microfilaments
• intermediate fibres

Question 15

What is the function of microtubules?

Answer 15

• globular tubular proteins polymerise to form tubes
• act as tracks for movements of organelles like vesicles around the cell
• determine the shape of the cell
• spindle fibres which have a role in the separation of sister chromatids are composed of microtubules

Question 16

What is the function of microfilaments?

Answer 16

• contractile fibres formed from the protein actin
• responsible for cell movement
• responsible for cell contraction during cytokinesis

Question 17

What is the function of intermediate fibres?

Answer 17

• these fibres give mechanical strength to help the cells maintain their integrity

Question 18

Give an example of a cell where microfilaments are important?

Answer 18

• phagocytes

- the behaviour of the active filaments determine the movement of phagocytes

Question 19

Describe the structure and function on cilia

Answer 19

• small hairlike structures
• help move substances along the cell surface
• cilia can be mobile or stationary
• each cilia contains two microtubules in the middle surrounded by nine pairs of microtubules in the shape of a wheel
• pairs of microtubules slide over each other which causes the cilia to move

Question 20

Mobile vs stationary cilia

Answer 20

• mobile cilia beat in a rhythmic manner causing fluids to move
• stationary cilia are present on the surface of many cells and they have roles in sensory organs such as the nose

Question 21

Why are compartments important in the cell?

Answer 21

• metabolic reactions require both specific enzymes and specific reaction conditions
• having different organelles… these compartments allow for specific conditions so specific cellular reactions can take place
• different sets of reactions take place in different parts of the ultrastructure of the cell