Lecture 9: Chloroplasts and Peroxisome

chloroplast genome

has its own genome

peroxisome genome

does not have its own genome

plastids

double membrane bound organelles found in plants and algae, formed an endosymbiotic relationship with eukaryotic plant and algae

chromoplast

contains pigments and synthesizes food via photosynthesis

chloroplasts

green color due to chlorophyll pigments found in higher plants and green algae

phaeoplast

dark brown color due to fucoxanthin pigments found in brown algae, diatoms and dinoflagellates

rhodoplast

red color due to phycoerythrin pigments, found in red algae

leucoplasts

non pigmented plastids that store food

amyloplast

stores starch

elaioplast

stores oil

proteinoplast

stores protein

proplastids

small, undifferentiated organelles

where do plastids develop from?

proplastids

chloroplast function

• fix CO2 in air into carbohydrates by photosynthesis

• generate energy

• synthesize amino acids, fatty acids and lipids for their compartments

• reduction of nitrite (NO2) to ammonia (NH3)

structure of chloroplast

• double membrane

• 3 compartments

double membrane of chloroplast permeability

• outer: porous

• inner: impermeable to ions and metabolites

3 compartments of the chloroplast

1. intermembrane space

2. stroma

3. thylakoid lumen

similarities of mitochondria and chloroplasts

• both have circular DNA

• both have a porous outer membrane

• both have inner membranes

approximate structural similarities of mitochondria and chloroplasts

• thylakoid lumen = intermembrane space

• stroma = matrix

chloroplast DNA

• sufficient tRNA → no wobble, 1/3rd of proteins made here

• lots of proteins also encoded by nuclear DNA

protein transport in chloroplast

• peptide passes Toc complex with Hsp70 (cytosol → intermembrane space)

• peptide passes Tic complex with Hsp93 ((intermembrane space → stroma)

• chaperone Hsp70 helps protein folding in stroma

location of Toc complex

outer membrane of chloroplast

location of Tic complex

inner membrane of chloroplast

sec pathway

SecA recognizes thylakoid signal seq, targets protein to Seq translocon using energy from ATP hydrolysis

TAT pathway

seq signal contains two arganine targets folded protein to TAT translocon using energy from protein gradient

SRP pathway

signal seq recognized by SRP (signal recognition particle) and pass through Abl3 translocase into the membrane

where do proteins incorporated into the thylakoid lumen come from?

the cytosol, they are transported to the thylakoid lumen

difference in mitochondria vs chloroplasts gradients

mitochondria has a chemical AND voltage gradient while chloroplasts only have a chemical gradient

two cycles of photosynthesis

• light cycle

• dark cycle (Calvin cycle)

location of light cycle

thylakoid membrane

what does the light cycle generate?

NADPH and ATP

how is energy generated in the light cycle?

H+ gradient

location of dark cycle (calvin cycle)

stroma

what does the dark cycle generate?

sugar

stages of the dark cycle (Calvin cycle)

1. fixation stage

2. reduction stage

3. regeneration stage

fixation stage

light independent reactions initialize- CO2 is fixed from inorganic to organic compound

reduction stage

ATP and NADPH reduce stuff

regeneration stage

RuBP is regenerated, starting the cycle over

peroxisome structure

a small, single membrane bound organelle

main function of peroxisome

oxidize certain organic molecules and degrade hydrogen peroxide from these reactions

catalase

breaks down H2O2 to H2O or uses it to oxidize another organic compound

peroxisome function in plants

• glyoxylate cycle to convert stored fatty acids into carbohydrates

• photorespiration to metabolize a side product of photosynthesis (2C sugar → glycine)

Zelleger spectrum disorders

defects in peroxisome leads to this disease, the result of dysfunctional lipid metabolism