Exercise 9:

Cytoskeletal Structures

Announcements• Post Lab 11 is due by your next lab.• LNA Cytoskeletal Structure assigned today, and is due

next lab (week of November 30).• Next Lab Exam 2 Review (week of November 30). • Exam 2: Week of December 7. Your exam time for

Exam 2 is the same as it was for Exam 1• Final Exam: Friday, December 11 from 8 – 11 AM• If you have a conflict with the Final Exam, you must fill

out the Conflict Final Exam Request Form found on the Course Website by December 9 at 5 PM.

Goals

• Become familiar with the three different cytoskeletal systems

• Understand the role and structures of the mitotic spindle during cell division

Cytoskeleton

• Composed of three distinct systems

• (classified by size)– Microfilaments (actin) - thinnest– Intermediate filaments (lamin)– Microtubules (tubulin)- thickest

Microfilaments (Actin)

Microfilaments

• Made up of strands of the protein actin and often interact with strands of other proteins.

• They change cell shape and drive cellular motion, including contraction, cytoplasmic streaming, and the “pinched” shape changes that occur during cell division.

• Microfilaments and myosin strands together drive muscle action.

Intermediate Filaments (Lamins)

Intermediate filaments

• Made up of fibrous proteins organized into tough, ropelike assemblages that stabilize a cell’s structure and help maintain its shape.

• Some intermediate filaments help to hold neighboring cells together (Cell junctions). Others make up the nuclear lamina.

Microtubules (Tubulin)

Microtubules

• Long, hollow cylinders made up of many molecules of the protein tubulin. Tubulin consists of two subunits, -tubulin and -tubulin.

• Microtubules lengthen or shorten by adding or subtracting tubulin dimers.

• Microtubule shortening moves chromosomes.

• Interactions between microtubules drive the movement of cells.

• Microtubules serve as “tracks” for the movement of vesicles.

The Exercise• Part I: Actin and Myosin Filaments

– View prepared slides of smooth, skeletal, and cardiac muscle – Draw each muscle type and label nucleus, sarcomere, I-disk, A & I

bands– You may find the Muscle Poster helpful

• Part II: Flagella and Cilia– Prepare slides – Observe the locomotion of each organism– Also available as prepared slides if needed

• Part III: Mitotic Spindle in plant and animal cells– View prepared slides of whitefish blastula and onion root tip– Compare/Contrast mitotic spindles found in plant and animal cells

Part I: Muscle Cells

Skeletal: voluntary movement, breathingSmooth: involuntary, movement of internal organs

Cardiac: beating of heart

Skeletal

Skeletal

Cardiac Muscle• Each muscle cell contains only one nucleus.• Adjoining cells interdigitate forming a meshwork

that is resistant to tearing (intercalated disk).

Smooth Muscle

• Long and spindled shaped.

• Each cell has a single nucleus

• Actin and myosin filaments are not regularly arranged and therefore, do not produce the striated appearance

Summary of Muscle Types

The Exercise

• Part I: Actin and Myosin Filaments– View prepared slides of smooth, skeletal, and cardiac muscle – Draw each muscle type and label nucleus, sarcomere, I-disk, A &

I bands

• Part II: Flagella and Cilia (microtubules)– Prepare slides with Protoslo– Observe the locomotion of each organism– Also available as prepared slides if needed

• Part III: Mitotic Spindle in plant and animal cells– View prepared slides of whitefish blastula and onion root tip– Compare/Contrast mitotic spindles found in plant and animal cells

Protozoa Cultures

• Amoeba• Ciliate

– Stentor• Flagellate

– Euglena

Amoeba

StentorCilia

EuglenaFlagella

#3

The Exercise

• Part I: Actin and Myosin Filaments– View prepared slides of smooth, skeletal, and cardiac muscle – Draw each muscle type and label nucleus, sarcomere, I-disk, A & I

bands

• Part II: Flagella and Cilia– Prepare slides – Observe the locomotion of each organism

• Part III: Mitotic Spindle in plant and animal cells – View prepared slides of whitefish blastula and onion root tip– Compare/Contrast mitotic spindles found in plant and animal cells

Mitotic Spindle

• Constructed to enable the separation of the chromatids formed during replication

• Consists of microtubules radiating out from the two centrosomes

• Centrosome consists of a pair of centrioles

Cell Division

The Mitotic Spindle Consists of Microtubules