B2.2 Organelles and Compartmentalisation

Question 1

What are organelles?

Answer 1

Discrete structures within a cell and perform a specific function

Examples include the nucleus, Golgi apparatus, mitochondria, lysosomes, chloroplasts, rough endoplasmic reticulum (RER), and smooth endoplasmic reticulum (SER)

Question 2

What is compartmentalisation in cells?

Answer 2

The use of membranes to isolate certain parts of the cell to form separate organelles. This allows reactions to occur without interference from other cellular processes.

Internal conditions (E.g. pH) can be differentiated in the cell to maintain optimum conditions for different enzymes;

Question 3

What is the function of the nucleus?

Answer 3

Houses nearly all the cell’s genetic material and makes ribosomes

The nucleus contains chromatin, which consists of DNA and proteins. Also contains nucleolus and the nuclear envelope

Question 4

What is the role of the nucleolus?

Answer 4

Part of Nucleus. Produces RNA, which is made into ribosomes

Ribosomes move out of the nucleus to the rough endoplasmic reticulum to produce proteins.

Question 5

What is the structure of the Nuclear envelope?

Answer 5

A dense, spherical structure which surrounds the nucleolus, and is made up of an inner and outer membrane, separated by a fluid.

It is marked with pores which allow for exchange of relatively large molecules.

Question 6

What is the function of the Cell membrane?

Answer 6

Semi-permeable layer that controls movement in and out of the cell.

Question 7

What is the function of the Golgi apparatus?

Answer 7

Processes and packages proteins, which are released in Golgi vesicles

The Golgi apparatus modifies proteins received from the rough endoplasmic reticulum.

Question 8

What are lysosomes and their function?

Answer 8

Contain hydrolytic enzymes for the destruction of microbes engulfed by white blood cells, and old organelles

Lysosomes are not present in plant cells.

Question 9

What is the advantage of compartmentalisation in cells?

Answer 9

Allows for optimal internal conditions, isolation of toxic substances, and flexibility in organelle positioning

Example: Phagocytic vacuoles isolate ingested materials.

Question 10

What is the structure of mitochondria?

Answer 10

Contains an inner and outer membrane, with the inner membrane folded into cristae

This structure increases surface area for ATP production.

Question 11

What is the role of vesicles in cells?

Answer 11

Transport and release substances produced by the cell by fusing with the cell membrane.

Vesicles can include transport vesicles, secretory vesicles, lysosomes, and peroxisomes.

Question 12

What does the chloroplast do?

Answer 12

Responsible for photosynthesis and contains pigments such as chlorophyll. Double-membrane bound organelle.

Chloroplasts are not present in animal cells.

Question 13

What is the function of clathrin?

Answer 13

Plays a role in the formation of vesicles in cells

Clathrin stabilizes membrane invaginations during processes like endocytosis and phagocytosis.

Question 14

What are the membranes in Chloroplasts?

Answer 14

Outermembrane, innermembrane, thylakoid membrane.

Compartment (space) between innermembrane and thylakoid membrane is called stroma.

Question 15

What is the role and structure of Chloropolasts?

Answer 15

Absorb light to create ATP. Disc-shaped structure increases surface area to hold chlorophyll and other enzymes needed for photosynthesis; this increases rate of photosynthesis.

Stack to form grana.

Question 16

What is the significance of the double membrane around the nucleus?

Answer 16

Acts as a barrier. Protects genetic material, prevents damage to DNA. Regulates the entry and exit of molecules

The nuclear pores allow for the exchange of substances.

Question 17

Describe the function of vacuoles.

Answer 17

Helps in osmotic balance and storage of substances

Vacuoles may also have hydrolytic functions similar to lysosomes.

Question 18

How does compartmentalisation aid in protein synthesis?

Answer 18

Allows mRNA to be modified before binding to ribosomes

This ensures functional proteins are produced.

Question 19

What is the matrix in mitochondria?

Answer 19

The enclosed space between the membranes (inner and outer) contains enzymes and other substances for respiration. Allows for high concentration gradients, which is required for respiration.

High concentration gradients form in the matrix, aiding respiration.

Question 20

What is the main function of the outer membrane of mitochondria?

Answer 20

Permeable to small molecules and ions. Contains transport proteins (porins), to assist transport of larger molecules into the mitochondria.

These transport proteins help larger molecules enter the mitochondria.

Question 21

What does the stroma in chloroplasts contain?

Answer 21

Enzymes and substrates required for the Calvin cycle

Compartmentalisation maximizes the efficiency of chemical reactions.

Question 22

What drives membrane curvature and the budding off of a vesicle?

Answer 22

Clathrin

Clathrin forms a lattice-like structure that is crucial for vesicle formation.

Question 23

What happens to the clathrin coat once the vesicle is internalized?

Answer 23

The clathrin coat disassembles

This allows the vesicle to be transported to its target destination.

Question 24

Through what process are low-density lipoprotein (LDL) particles internalized?

Answer 24

Clathrin-mediated endocytosis

This process provides cholesterol for cellular processes.

Question 25

What role does clathrin play in phagocytosis?

Answer 25

Stabilizes membrane invaginations ## Footnote Clathrin aids in the final stages of vesicle formation during phagocytosis.

Question 26

Which type of cells use clathrin-mediated vesicles to engulf and digest bacteria?

Answer 26

Macrophages ## Footnote Macrophages are immune cells that perform phagocytosis.

Question 27

What is the function of clathrin-coated vesicles in lysosome formation?

Answer 27

Transport enzymes like acid hydrolases ## Footnote This ensures the proper functioning of lysosomes in breaking down macromolecules.

Question 28

What is a key example of an enzyme transported to lysosomes by clathrin-coated vesicles?

Answer 28

Mannose-6-phosphate-tagged enzymes ## Footnote These enzymes are crucial for lysosomal function.

Question 29

What is the significance of compartmentalisation in cells?

Answer 29

Development of specialised cell structures ## Footnote This allows for the concentration of reactants and separation of damaging chemicals.

Question 30

Which structures are not considered organelles?

Answer 30

Cytoskeleton, cell wall, and cytoplasm ## Footnote While they are important for cell function, they do not fit the definition of organelles.

Question 31

Which organelles have highly folded membranes to increase surface area?

Answer 31

Mitochondria and chloroplasts ## Footnote This adaptation allows for more efficient production of ATP and glucose.

Question 32

What is the protective role of the double membrane of the nucleus?

Answer 32

Serves as a barrier for genetic material ## Footnote It regulates the entry and exit of molecules critical for gene expression.

Question 33

What is the function of the rough endoplasmic reticulum (ER)?

Answer 33

Produces proteins for export outside the cell ## Footnote It has attached ribosomes that facilitate this process.

Question 34

What are vesicles?

Answer 34

Small membrane-bound structures that transport and store materials ## Footnote They include proteins, lipids, and RNA.

Question 35

Outline the difference between bound and free ribosomes.

Answer 35

Bound ribosomes produce proteins for export; free ribosomes produce proteins for internal use ## Footnote This distinction is important for understanding protein targeting.

Question 36

List solid organelles (no membrane), single-membrane enclosed organelles and double-membrane enclosed organelles.

Answer 36

Solid: Ribosomes, Centrioles, Nucleolus. Single membrane: ER, Golgi apparatus, Lysosomes, and Vacuoles. Double membrane: Nucleus, mitochondria, cytoplasm.

Question 37

Why are cytoplasm, cel wall and cytoskeleton not considered organelles?

Answer 37

They do not fit the definition of an organelle: do not perform a specific function. Doesn't do anything to aid in carrying out of 7 life functions. ## Footnote Cytoplasm is medium; provides space for organelles to perform functions. Cell wall: provide support and regulate movement of substances in and out.

Question 38

Advantages of Compartmentalization of DNA in nucleus from cytoplasm

Answer 38

Nucleus protects DNA from potential damage from chemical reactions in cytoplasm. Allows for gene transcription and translation to be kept separate.

Question 39

Location and timing of initiation of transcription and translation in Prokaryotic cells.

Answer 39

Location: they both occur simultaneuosly in the cytoplasm. This is because Prokaryotes lack a nucleus and membrane-bound organelles. Timing: both happen in a coupled manner. As soon as the mRNA is transcribed, ribosomes attach to it and begin translating the genetic code into proteins.

Question 40

Location and timing of initiation of transcription and translation in Prokaryotic cells.

Answer 40

Location: Transcription occurs within the nucleus, while translation takes place in the cytoplasm. This separation is due to the presence of a nuclear membrane in eukaryotic cells. Timing: Transcription and translation are separated in time. The mRNA molecule undergoes processing (including capping, splicing, and polyadenylation) within the nucleus before being transported to the cytoplasm for translation.

Question 41

Advantages of Comparmentalization within cells.

Answer 41

Increases efficiency of metabolic processes: compartmentalization allows for the concentration of enzymes and substances in a specific area. Creating optimial conditions in compartments for different reactions (pH, ion and substrate concentration) Protecting cellular components.

Question 42

Structure and function of outer membrane in Mitochondria

Answer 42

Separates contents of Mitochondrion from rest of the cell, allowing different, more ideal conditions for aerobic respiration. Selectively permeable: only allows certain materials in and out.

Question 43

Structure and function of inner membrane in Mitochondria

Answer 43

Inner membrane contains carriers and the transmembrane integral enzyme ATP synthase, enabling ETC and production of ATP via chemiosmosis and oxidative phosphorylation.

Question 44

Structure and function of intermembrane space in Mitochondria

Answer 44

Space and volume between outer and inner membrane: very small and consistent. Allows rapid accumulation of protons and building of a gradient relative to matrix necessary for chemiosmosis.

Question 45

Structure and function of cristae in Mitochondria

Answer 45

Inner membrane highly folded into invaginations called Cristae. Increases membrane surface area: increases rate of ATP production.

Question 46

Structure and function of Matrix in Mitochondria

Answer 46

Fluid inside matrix has different optimal pH and contains a high conc. of enzymes and substrates needed for link reaction and Krebs cycle.

Question 47

Structure and Function of ribosome and mtDNA in Mitochondria

Answer 47

DNA allows it to replicate and make more copies of itself, independent to rest of the cell. DNA transcribed into mRNA and 70s ribosomes allows it to synthesize its own proteins.

Question 48

Structure and function of double membrane in Chloroplasts

Question 49

Structure and function of thylakoid membrane in Chloroplasts

Question 50

Structure and function of photosystems in Chloroplasts

Question 51

Structure and function of compact thylakoid lumen in Chloroplasts

Answer 51

The space and volume within thylakoid is very small. Allows rapid accumulation of protons and building of a gradient relative to matrix necessary for chemiosmosis.

Question 52

Structure and function of stroma in Chloroplasts

Answer 52

Fluid inside stroma has different optimal pH and contains a high concentration of enzymes and substrates needed for light-independent reactions (Calvin cycle)

Question 53

Structure and function of ribosomes and cpDNA in chloroplasts

Answer 53

DNA allows it to replicate and make more copies of itself, independent to rest of the cell. DNA transcribed into mRNA and 70s ribosomes allows it to synthesize its own proteins.

Question 54

How are proteins synthesized and released out of the cell (bound ribosomes).

Answer 54

mRNA copy of the instructions (genes) for (a hormone for example) made in nucleus. mRNA leaves nucleus through a nuclear pore. mRNA attaches to a ribosome attached to the endoplasmic reticulum. Ribosome reads instructions and assembles the protein. Hormone molecules are pinched off in vesicles and travel towards Golgi apparatus. Vesicle fuses with Golgi apparatus. Golgi apparatus processes and packages hormone molecules ready for release. Packaged hormone molecules are pinched off in vesicles from Golgi apparatus and moves towards cell surface membrane. Vesicle fuses with cell surface membrane. Cell surface membrane opens to release hormone molecules out of cell.

Question 55

Structure and Function of Golgi apparatus

Answer 55

A stack of membrane bound sacs organized into cis, medial and trans compartments: - cis: compartment receives newly modified proteins from RER. - medial: compartment where they undergo further modification. - trans: compartment where they get packaged into vesicles for secretion.

Question 56

Describe the role of Clathrins in the formation of vesicles

Answer 56

Clathrins are a protein. Molecules bind to specific receptors embedded on the outside of the plasma membrane. Clathrin binds to these receptors, causing the membrane to invaginate. Many of these Clathrins come to form a cage-like lattice around the invagination, forming a vesicle that buds off. Once the vesicle is budded off, Clathrins and receptors removed.