A Tour of the Cell, cont…

Last Time: The Nucleus and the Endomembrane System

Today: Other Organelles and the Cytoskeleton

Cells need energy to work

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Sunlight photosynthesis ⏐ → ⏐ ⏐ ⏐ ⏐ glucose

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Glucose cell respiration ⏐ → ⏐ ⏐ ⏐ ⏐ ATP

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ATP hydrolysis ⏐ → ⏐ ⏐ ⏐ ADP + energy

Figure 6.8 The structure and hydrolysis of ATP

Chloroplasts in plant cells convert sunlight into chemical energy that will

be used to make ATP

ATP is manufactured through cellular respiration that takes place in the mitochondria

Peroxisomes

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H2 +O2 → H2O2

H2O2 +H2 → 2H2O

The cytoskeleton

MicrofilamentsActin

Two intertwined strands

• maintain cell shape by resisting tension

Actin subunit

Protein subunits

Structure

Functions

• motility via pseudopodia • muscle contraction

• cell division in animals

7 nm

Intermediate filamentsKeratin, others

Fibers wound into thick cables

• anchor nucleus and some other organelles

Microtubules-tubulin and -tubulin dimers

Hollow tube

Keratin subunits Tubulin dimer

• maintain cell shape by resisting compression

• motility via flagella/cilia

• move chromosomes during cell division

• move organelles

10 nm 25 nm

3 types of cytoskeletal structures

Structure of kinesin

Tail

Stalk

Head

Motor molecules like kinesin, myosin, and dynein work with the cytoskeleton to produce

movement

Transport vesicle

Kinesin

Microtubule

ATP ADP+Pi

Kinesin "walks" along a microtubule track

ATP ADP+Pi

Microfilaments and Intermediate Filaments

Networks of filaments near the plasma membrane help to maintain a cell’s shape

Microfilaments aid in motility

Centrosome containing a pair of centrioles

Microtubules often grow out from the region called the centrosome

Cilia Flagella

Cilia and Flagella move the entire cell

TEM of flagella

Microtubule doublet

Cell membrane

Central pair

Outer doublet

Dynein

Spoke

Cilia and Flagella have a “9 +2” arrangement of microtubule doublets

Bend

The motor protein Dynein “walks” along the microtubules within the flagella on one side,

causing bending

Figure 7.23 A comparison of the beating of flagella and cilia

Plant cells are surrounded by cell walls made of cellulose

Plasmodesmata connect adjacent plant cells

Animal cells are connected through Intercellular junctions

Review of an animal cell

(centrioles)

Review of a plant cell