7: Extracellular Structures and Cell Movement in Biology

Actin Filaments (Microfilaments)

Enable cell crawling and shape changes.

Microtubules

Provide structural support and facilitate movement of organelles and vesicles.

Actin Filaments (Microfilaments)

Enable cell crawling and shape changes.

Microtubules

Provide structural support and facilitate movement of organelles and vesicles.

Intermediate Filaments

Act as intracellular tendons, preventing excessive stretching of cells.

Crawling

Cells extend and retract using actin filaments and myosin motors.

Swimming

Cells use cilia or flagella composed of microtubules.

Actin Polymerization

At the leading edge of the cell, actin filaments rapidly polymerize, pushing the cell membrane forward.

Myosin Contraction

Myosin motors pull on actin filaments, dragging the rest of the cell forward.

Microtubule Stabilization

Microtubules polymerize into the newly extended region, stabilizing the cell's forward movement.

White Blood Cells

Crawl out of blood vessels to reach sites of infection or injury.

Cancer Cells

Use crawling to spread (metastasize) to other tissues.

9 + 2 Array

Both flagella and cilia have a core of 9 pairs of microtubules surrounding 2 central microtubules.

Dynein Arms

Motor proteins that cause microtubules to slide past each other, producing movement.

Basal Body

Anchors the flagellum or cilium to the cell and organizes the microtubules.

Flagella

Long, whip-like structures used for swimming (e.g., sperm cells).

Cilia

Short, hair-like structures that can move cells or fluids (e.g., cilia in the trachea move mucus and trapped particles out of the respiratory tract).

Protists

Use flagella or cilia to move through water.

Human Cells

Cilia in the trachea help clear debris, and cilia in the ear detect sound waves.

Primary Cell Wall

Laid down during cell growth, composed of cellulose fibers.

Secondary Cell Wall

Added inside the primary wall in fully grown cells, providing additional strength.

Middle Lamella

A sticky layer between adjacent cell walls that glues cells together.

Extracellular Matrix (ECM)

A network of glycoproteins (e.g., collagen, elastin) that supports and communicates with cells.

Collagen

Strong fibrous protein that provides strength and flexibility.

Elastin

Provides elasticity to tissues.

Proteoglycans

Glycoproteins that form a gel-like matrix, providing cushioning and hydration.

Fibronectin

Links the ECM to the cell membrane via integrins.

Comparison of Cytoskeletal Elements

Actin Filaments: Cell crawling, shape changes; Microtubules: Organelle movement, cilia/flagella; Intermediate Filaments: Structural support.