Chloroplast, other plastids, and Peroxisomes Unit 6

What are the three membrane systems or compartments that organize a chloroplast

A chloroplast has an outer and inner envelope membrane, plus an internal thylakoid membrane system. Its main compartments are the intermembrane space, stroma, and thylakoid lumen.

What is the function of the thylakoid membrane

The thylakoid membrane contains the photosynthetic electron transport machinery that pumps protons into the thylakoid lumen and helps generate ATP.

What are grana in chloroplasts

Grana are stacks of flattened, disc-shaped thylakoids.

What is the stroma, and what important processes occur there

The stroma is the fluid-filled compartment inside the inner envelope membrane. It contains chloroplast DNA, gene-expression machinery, and enzymes involved in converting CO₂ into carbohydrates.

How is the thylakoid membrane functionally similar to the inner mitochondrial membrane

Both contain electron transport chains that pump protons across the membrane, creating a gradient that drives ATP synthesis.

What is the difference between the chloroplast envelope and the thylakoid membrane in photosynthesis

The thylakoid membrane carries out the light-dependent electron transport and proton pumping, while the stroma contains enzymes that use the resulting energy to help convert CO₂ into carbohydrates.

How do the outer and inner chloroplast envelope membranes differ in permeability

The outer membrane contains porins that allow small molecules to pass, while the inner membrane requires specific transporters for most ions and metabolites.

What are two major similarities between chloroplasts and mitochondria

Both generate metabolic energy, contain their own genomes, and can divide within the cell.

What are two important functions of chloroplasts besides photosynthesis

They synthesize molecules such as amino acids, fatty acids, and membrane lipids, and they help assimilate nitrogen by reducing nitrite to ammonia.

How do chloroplasts generate ATP during photosynthesis

Light-driven electron transport pumps protons into the thylakoid lumen, and protons flowing back into the stroma drive ATP synthesis.

Chloroplast DNA encodes a small subset of chloroplast proteins, while most chloroplast proteins are encoded by nuclear genes and imported into the organelle.

How does the chloroplast genome compare with the mitochondrial genome

Both are separate from the nuclear genome and encode some organelle proteins, rRNAs, and tRNAs. However, chloroplast genomes generally encode more genes than mitochondrial genomes.

Where are most chloroplast proteins synthesized

Most chloroplast proteins are synthesized on free ribosomes in the cytosol before being imported into the chloroplast.

What is a transit peptide, and what is its function

A transit peptide is a targeting sequence on a newly synthesized protein that directs it to the chloroplast for import. It is usually removed after the protein enters the chloroplast.

What are the functions of the TOC and TIC complexes

TOC is the translocon in the outer chloroplast envelope membrane, while TIC is the translocon in the inner envelope membrane. Together, they help transport proteins into the chloroplast.

How does a protein destined for the chloroplast stroma enter the organelle

Its transit peptide directs it to the TOC complex, and the protein passes through TOC and TIC across the two envelope membranes into the stroma. The transit peptide is then typically removed.

How do chloroplast proteins destined for the thylakoid membrane or lumen reach their final destination

After entering the stroma, they use additional targeting signals and specialized transport machinery to reach the thylakoid membrane or cross it into the thylakoid lumen.

What are the three main pathways used to transport proteins across or into the thylakoid membrane

The Sec pathway, Tat pathway, and cpSRP pathway help deliver different proteins to the thylakoid system.

What is the main difference between the Sec and Tat pathways in chloroplasts

The Sec pathway generally transports proteins in an unfolded state, whereas the Tat pathway can transport proteins that have already folded.

What is the role of the chloroplast signal recognition particle, or cpSRP

cpSRP helps target certain proteins, especially light-harvesting proteins, to the thylakoid membrane for insertion.

What are plastids, and how do they differ in function

Plastids are organelles in plant cells that perform specialized functions, including photosynthesis, pigment storage, and nutrient storage.

What is the main function of chromoplasts

Chromoplasts synthesize and store pigments, especially carotenoids, that give flowers and fruits yellow, orange, or red colours.

What are leucoplasts, and what is their main function

Leucoplasts are colourless plastids that specialize in synthesizing or storing substances such as starches, oils, and proteins.

What are amyloplasts, and what do they store

Amyloplasts are plastids specialized in synthesizing and storing starch.

What are elaioplasts, and what do they store

Elaioplasts are plastids specialized in storing oils and other lipids.

How do chloroplasts and chromoplasts differ in function

Chloroplasts carry out photosynthesis using chlorophyll, while chromoplasts mainly produce and store pigments that contribute to yellow, orange, and red colours.

How do leucoplasts differ from chloroplasts in appearance and function

Leucoplasts lack the prominent photosynthetic pigments found in chloroplasts and specialize in storing or synthesizing substances such as starch, oils, and proteins rather than carrying out photosynthesis.

Why can different plastids be considered specialized forms of the same organelle family

They share a common plastid identity but are specialized for different functions, such as photosynthesis, pigment production, or nutrient storage.

How does the function of an amyloplast benefit a plant

It stores starch as an energy reserve that the plant can use when needed.

Why are different types of plastids important to plant cells

They allow plant cells to specialize in different tasks, including capturing light energy, producing pigments, and storing nutrients.

What are the main functions of peroxisomes in animal cells

Peroxisomes contain enzymes that break down fatty acids and detoxify harmful substances, including hydrogen peroxide.

What is the role of catalase in peroxisomes

Catalase converts hydrogen peroxide (H₂O₂), which can damage cells, into water and oxygen.

Why is hydrogen peroxide produced and broken down in peroxisomes

Some peroxisomal oxidative reactions produce hydrogen peroxide as a by-product. Catalase breaks it down to prevent oxidative damage to the cell.

What is the role of peroxisomes in fatty acid oxidation

Peroxisomes break down fatty acids, especially very-long-chain fatty acids, into shorter molecules that can be used in other metabolic pathways.

What are two important functions of peroxisomes in plant cells

They participate in fatty acid breakdown and photorespiration. Specialized peroxisomes also help convert stored fats into sugars during seed germination.

What is the glyoxylate cycle, and why is it important in plants

The glyoxylate cycle allows plants, especially germinating seeds, to convert products of fatty acid breakdown into compounds that can be used to produce carbohydrates.

How are proteins targeted to peroxisomes

Proteins contain specific peroxisomal targeting signals that are recognized by receptor proteins, which direct them to the peroxisome.

What are PTS1 and PTS2 in peroxisomal protein import

PTS1 and PTS2 are peroxisomal targeting signals that direct proteins to peroxisomes. They are recognized by different receptors: Pex5 recognizes PTS1, while Pex7 recognizes PTS2.

How do peroxisomes obtain their membrane proteins and grow

Peroxisomal membrane proteins can be supplied through the endoplasmic reticulum, and existing peroxisomes can grow and divide to produce new peroxisomes.

What are the two main pathways by which peroxisomes are formed

Peroxisomes can form by growth and division of existing peroxisomes or through a de novo pathway involving the endoplasmic reticulum.