B2.2 Organelles and Compartmentalization

Question 1

define organelle

Answer 1

organelle = a discrete structure within a cell that is adapted to perform a specific function

Question 2

identity organelles in this image

Answer 2

nucleus, Golgi, mitochondria, lysosomes, chloroplast, RER, SER

Question 3

what is compartmentalisation? what does it do?

Answer 3

• compartmentalisation = the organisation of different functions and processes within specific subcellular structures separated by plasma membranes
• it allows for the development of specialised cell structures such as the chloroplasts and mitochondria

Question 4

• Organelles can be found in _____ cells
• However, membrane-bound organelles are only found in ___

Answer 4

• Organelles can be found in both prokaryotic and eukaryotic cells
• However, membrane-bound organelles are only found in eukaryotic cells

Question 5

an example of compartmentalisation in cells?

Answer 5

membrane-bound organelles

Question 6

what is the advantage of compartmentalisation in cells?

Answer 6

main advantage:

• it allows the cell to separate chemical reactions and other cellular processes

–> this allows the cell to increase the rate of chemical reactions

other advantages:

• allows specific reactions to occur in specific places
• enables maintenance of different internal conditions
• allows isolation of toxic or damaging substances
• supports flexibility in organelle number and positioning based on the cell’s current needs

Question 7

List solid organelles (not membrane-bound)

Answer 7

ribosomes

• they are responsible for protein synthesis
• they have a specific function, SO, even though they are not membrane-bound, they are considered organelles

Question 8

List organelles enclosed by a single membrane

Answer 8

1. Lysosomes

• Contain enzymes to break down waste and cellular debris

2. Peroxisomes

• Involved in the breakdown of fatty acids and detoxification of harmful substances

3. Vacuoles

• Storage structures for water, nutrients, and waste

4. Golgi apparatus

• Modifies, sorts, and packages proteins and lipids

5. Endoplasmic reticulum

• includes both rough (with ribosomes for protein synthesis) and smooth (involved in lipid synthesis and detoxification)

Question 9

List organelles enclosed by a double membrane

Answer 9

1. Mitochondria

• produces energy (ATP) through cellular respiration

2. Chloroplasts

• Site of photosynthesis

3. Nucleus

• Contains the cell’s genetic material (DNA) and controls cell activities

Question 10

why is the cell wall not considered to be an organelle?

Answer 10

BECAUSE IT:

• Is not surrounded by a membrane
• Does not participate in metabolic processes

Question 11

why is the cytoskeleton not considered to be an organelle?

Answer 11

BECAUSE IT:

• Is not membrane-bound
• Is not involved in metabolism

Question 12

why is the cytoplasm not considered to be an organelle?

Answer 12

BECAUSE IT:

• Does not have a specific function by itself
• Is not enclosed by a membrane
• Is not a discrete structure

Question 13

what are the benefits of DNA in the nucleus being compartmentalized from the cytoplasm? (4)

Answer 13

• allows for better regulation of gene expression, as transcription can be controlled separately from translation
• enables post-transcriptional modification of mRNA before it is translated into protein
• allows for signals from the cytoplasm to influence gene expression by modifying transcription levels
• protects DNA from potentially damaging metabolic reactions occurring in the cytoplasm

Question 14

Compare the location and timing of initiation of transcription and translation between prokaryotic and eukaryotic cells

Answer 14

In prokaryotic cells:

• Both transcription and translation occur in the cytoplasm
• Translation often begins while transcription is still ongoing (meaning that the protein is produced soon after mRNA is made)

In eukaryotic cells:

• Transcription occurs in the nucleus, and translation occurs in the cytoplasm
• These processes are separated in time and space, allowing for mRNA to be modified before translation begins

Question 15

what is post-transcriptional modification?

Answer 15

post-transcriptional modification = changes to mRNA after transcription that are necessary for a working protein to be produced

Question 16

why is post-transcriptional modification of RNA impossible in prokaryotic cells?

Answer 16

• Prokaryotic cells lack a nucleus, so transcription and translation occur in the same space—the cytoplasm

–> SO, because translation begins almost immediately after transcription, there is no opportunity to modify mRNA

Question 17

Why is it important that lysosomes are compartmentalized in the cell?

Answer 17

• Lysosomes contain powerful digestive enzymes (like proteases and lipases)
• SO, by keeping them enclosed in a membrane (keeping them compartmentalized), the cell prevents these enzymes from digesting important cellular components

–> keeping them compartmentalized prevents damage to the rest of the cell

Question 18

What is a phagocytic vacuole?

Answer 18

A membrane-bound compartment formed when a cell engulfs pathogens or debris during phagocytosis

Question 19

Why must phagocytic vacuoles be compartmentalized? what are the benefits?

Answer 19

To isolate potentially harmful materials like bacteria or toxins from the rest of the cell

–> it helps support immune function by allowing white blood cells to trap and destroy pathogens safely inside the cell without damaging the cytoplasm

Question 20

What happens when a phagocytic vacuole fuses with a lysosome?

Answer 20

The contents are digested by lysosomal enzymes in a safe, enclosed environment