Cellular Organelles and membrane trafficking (3)

What are organelles?

Membrane related

What did eukaryotic cells evolve?

Membrane-bounded compartments

What are these compartments specialised for?

• Provide energy

• Synthesize lipids, carbohydrates, proteins, and nucleic acids

• Degrade cellular constituents

What is the origin of mitochondria and chloroplasts?

Mitochondria and chloroplasts both arose from endosymbiotic bacteria

What do mitochondria and chloroplasts retain?

Remanets of those prokaryotic genomes

What did these organelles bring to eukaryotic cells?

Biochemical mechanisms that allow their eukaryotic hosts to acquire and use energy more efficiently

How is energy used in mitochondria and chloroplasts?

Energy from the breakdown of nutrients or from absorption of photons is used to energize electrons

What happens to mitochondria and chloroplasts as membrane organelles?

Both mitochondria and chloroplasts fuse and split

What is the function of oxidative phosphorylation in mitochondria?

Energy is extracted to create proton gradients. These proton gradients drive the rotary adenosine triphosphate (ATP) synthase and create ATP

What is the structure of mitochondria?

Mitochondria consist of two membrane-bounded compartments, one inside the other. The outer membrane surrounds the intermembrane space. The inner membrane surrounds the matrix

What is special about mitochondrial membranes and compartments?

Each membrane and compartment has a distinct protein composition and functions

What type of DNA do mitochondria contain?

Circular DNA – 1000 copies in a vertebrate cell

What pathways supply energy to mitochondria?

Glycolysis and fatty acid oxidation

What do these pathways produce?

Pyruvate + ATP NADH

What do these pathways feed into?

Citric acid cycle (Krebs cycle) of energy-yielding reactions in the mitochondrial matrix

What molecule enters the citric acid cycle?

Acetyl-CoA

What happens during one turn of the citric acid cycle?

Breakdown of acetyl-CoA

What is produced in one turn of the citric acid cycle?

• Three molecules of NADH (nicotinamide adenine dinucleotide)

• One molecule of FADH2 (flavin adenine dinucleotide)

• Two molecules of carbon dioxide

What do NADH and FADH2 do?

Energetic electrons donated by NADH and FADH2 drive an electron transport pathway in the inner mitochondrial membrane

Where does the respiratory chain occur?

Inner mitochondrial membrane

What is the respiratory chain?

It is an oxidative chain

Why is energy used in the respiratory chain?

Energy is used to transfer multiple protons

How does the respiratory chain work?

Creating a H+ gradient

What is the end product of the respiratory chain?

Oxidative phosphorylation of ATP

What are thylakoids?

Membrane-bound compartments inside chloroplasts and cyanobacteria

What are stroma and periplasm?

Internal cellular compartment separated from the thylakoid space

What is chlorophyll?

Pigment in algae and plants to capture the remarkable amount of energy carried by single photons to boost electrons to an excited state

What is a pigment?

A molecule that can change state in contact with photons

What do thylakoid membranes contain?

Photosynthetic hardware and enclose the thylakoid membrane space

What is the function of the chloroplast inner membrane?

Permeability barrier, containing carriers for metabolites

What does the inner membrane surround?

The stroma

What is the stroma?

The cytoplasm of the original symbiotic bacterium, a protein-rich compartment devoted to synthesis of three-carbon sugar phosphates, chloroplast proteins, and all plant fatty acids

What else does the stroma contain?

Houses the chloroplast genomes and stores starch

What is the function of the outer membrane?

Has large pore channels that allow free passage of metabolites

What does the Type II photosystem contain?

Components to assemble a transmembrane complex of proteins, pigments, and oxidation/reduction cofactors called a reaction center

What electron acceptors are used in reaction centers of purple bacteria and green filamentous bacteria?

The pigment pheophytin and a quinone as the electron acceptor

What are these reaction centers similar to?

Photosystem II of cyanobacteria and chloroplasts

What electron acceptors are used in reaction centers of green sulfur bacteria and heliobacteria?

Iron-sulfur centers

What are these reaction centers similar to?

Photosystem I of cyanobacteria and chloroplasts

How are the energy levels in this reaction different?

Lower

What electron acceptors are used in reaction centers of purple bacteria and green filamentous bacteria?

The pigment pheophytin and a quinone as the electron acceptor

What are these reaction centers similar to?

Photosystem II of cyanobacteria and chloroplasts

How are special-pair chlorophylls in photosystem I excited?

Direct absorption of light or resonance energy transfer from surrounding light-harvesting complexes

Where do excited-state electrons move within the reaction center?

From these chlorophylls through two accessory chlorophylls to an iron-sulfur center

Where do electrons move after the iron-sulfur center?

To the iron-sulfur center of a subunit on the cytoplasmic side of the membrane