Mitochondria, Chloroplasts, Peroxisomes, & the Cytoskeleton

6.5-6.7

Mitochondria & Chloroplasts are special…Not part of the endomembrane system because…

They both have 2 membranes separating their insides from the cytosol

Have their own ribosomesContain small amounts of their own DNA to make

some of their own membrane proteinsGrow and reproduce independently of the cell

MitochondriaFound in eukaryotic cells of plants,

animals, fungi, and protistsMore active cells have more

mitochondriaVery small - ~ 1-10 microns

Structure of Mitochondria2 membranes

Smooth outer membraneConvoluted inner membrane

Folds called cristaeThis membrane creates 2 spaces

inside the mitochondrionSpace between outer & inner

membrane = intermembrane spaceSpace inside inner membrane = matrix

Matrix has enzymes , DNA, ribosomes

Lots of folds means lots of membrane surface for cell respiration to occur

ChloroplastsOne of a family of plant organelles

called plastidsAmyloplast – store starchChromoplast – pigments that color

fruits and flowersChloroplast – contain the pigment

chlorophyll & enzymes for photosynthesisVery small ~ 2 micronsFound in green parts of plants

Structure of ChloroplastsDouble membrane with narrow

intermembrane space Inside is second membrane system –

flattened discs called thylakoidsStacks of thylakoids are called granaFluid inside grana called stroma

Stroma contains DNA, enzymes for photosynthesis, ribosomes

Quick ThinkDescribe at least 2 things that

mitochondria and chloroplasts have in common.

Explain why mitochondria and chloroplasts are not part of the endomembrane system.

PeroxisomesSingle membraneContain enzymes that transfer

hydrogen from other molecules to oxygen to produce H2O2 as a by-product.

Contains enzymes that then break down H2O2 into water.

PeroxisomesMany different functionsSome are used to break down fatty acidsThose in the liver detoxify alcohol

The CytoskeletonCytoskeleton - a network of

fibers that runs through the cellHelps organize the inside of the

cellMade up of 3 types of tubes:

MicrotubulesMicrofilamentsIntermediate filaments

Cytoskeleton Functions

Supports cellMaintains cell shape

(important for animal cells since no cell wall)

Can be dismantled and reformed quickly so cells can change shape

Cytoskeleton Function

Aides in cell motility -2 types of motility:Whole cell movement - the cytoskeleton

interacts with motor proteins to allow the cell to move along fibers outside the cell

Movement of organelles and vesicles within the cell - internal parts move along filaments of cytoskeleton

Sperm around an egg

Cytoskeleton Structure

Microtubules - thickestMicrofilaments - thinnest (aka

actin filaments)Intermediate filaments - mid

sized

Microtubules

HollowMade of a protein called tubulinGive shape & support to cellAllows for organelles to move

along themSeparate chromosomes during

cell divisionGrow out of centrosomes in many

cells

Cilia & FlagellaSpecialized arrangement of microtubules makes flagella &

cilia beat Internal structure of both the same

Core of microtubules surrounded by plasma membrane9 doublets of microtubules arranged in a ringWagon wheel proteins that connect each doubletMotor proteins between each doubletWhole thing anchored to cell at the basal body

Cilia & Flagella Flagella on spermCilia on cells in the throat move mucus alongCilia in reproductive tract of females moves egg

toward uterusLots of unicellular eukaryotes use cilia and flagella

for movement in aquatic environments

Microfilaments (Actin Filaments)

SolidBuilt from a protein called actinHelp support cell’s shapeHave an important role in muscle

contraction

Intermediate FilamentsSpecialized for bearing tensionMade up of keratin proteinsMore diverse than the other 2More permanent than the other 2

Skin is dead cells full of keratin proteins

Keep certain organelles, like nucleus, locked in place

Maintain shape of cell, especially odd shapes like neurons

Quick Think – complete the tableMain features Main functions

Microtubules Hollow, thickest, tubulin

support for cell, organelles move along it’s tracks, cilia & flagella

Microfilaments Thinnest, solid

actin

Support cell shape, muscle contraction

Intermediate filaments

In between size, diverse structure, more permanent, keratin

Lock certain organelles in place, maintain irregular cell shapes

Quick ThinkThere are many different cell types, even

within the same organism. Cells vary in size, shape, structure, and function. This is part of the diversity of life.

Which aspects of cells best reveal their evolutionary unity?

What are some examples of specialized cellular modifications?