Chapter 7

Cell Structure & Function

Scientists & Discoveries

• Early 1600’s (Holland): 1st

microscope was constructed

• Anton van Leeuwenhoek (1600’s) used single lens as a microscope to study and very carefully draw tiny living organisms

• (1665) English physicist Robert Hooke used light microscope to study thin slices of plants-saw cork had many tiny chambers he called “cells” like monastery cells

• cells= the basic units for all forms of life

• (1838) Matthias Schleiden -concluded all plants made of cells

• (1839) Theodor Schwann - animals made of cells

• (1855) Rudolf Virchow -studied cell reproduction; 5yrs research concluded with: “Where a cell exists, there must have been a preexisting cell…”

The Cell Theory

• All living things are composed of cells

• Cells are the basic units of structure and function in living things

• New cells are created from existing cells.

Basic Cell Structures

• Cells usually measure 5-50 micrometers

• Smallest: measures 0.2 micrometers

• Largest: (amoeba Chaos chaos) 1000 micrometers

• All cells have a cell membrane and cytoplasm

• Cell membrane: thin flexible barrier around a cell

• Cytoplasm: material inside the cell membrane

• Many cells also have cell wall (strong layer around cell membrane)

• Cell membranes & cell walls support & protect cells while allowing them to interact with their environment

• Some cells also have a nucleus (a large structure that stores the cells genetic information & controls the cells activities)

Prokaryotes vs. Eukaryotes

• Cells are divided into 2 categories:

1. Prokaryotes

2. Eukaryotes

*divided into these 2 categories to separate cells that contain a nucleus and organelles (eukaryotes) and those that do not (prokaryotes)

Prokaryotes

• Usually smaller & simpler than eukaryotes• Contain cell membranes & cytoplasm• DO NOT have nuclei• All bacteria are prokaryotes - examples: Escherichia coli (intestines),

Staphylococcus aureus (skin infections)

Prokaryotes• Carry out all activities that define life (grow, reproduce, respond to their environment, & some even move)

Eukaryotes

• CONTAIN nuclei, cell membrane, cytoplasm, & dozens of other specialized structures that perform special functions (organelles)

• Some are single celled organisms, but most make up multicellular organisms

• All plants, animals, fungi, and many microorganisms are eukaryotes

Eukaryotes

Section 2: Cell Structures• A. Cytoplasm- refers to

the region outside the nucleus but inside the cell membrane

B. Cell Membrane

• Also called the plasma membrane

• Bi-layer phospholipids that regulates what enters and leaves the cell

C. Cell Wall

*main function=provide support & protection for the cell

*located outside cell membrane

*found in plants and algae & nearly all eukaryotes (not animal cells)

• In plants the cell wall is

composed of cellulose

• In fungi the cell wall contains

chitin

• In bacteria it contains peptidoglycan

C. Nucleus*controls most of the cell

processes & contains hereditary information of DNA

*chromatin-granular material in the nucleus that consists of DNA bound to protein

*chromosomes-condensed chromatin that consists of genetic information that is to be passed on during cell division

(Nucleus contd.)

*Nucleolus-small , dense region where assembly of ribosomes begins

*Nuclear envelope- double-membrane layer that surrounds the nucleus. It contains many nuclear pores that allow material to move in/out of the nucleus

D. Cytoskeleton

*network of protein

filaments that help

the cell to maintain

its shape, also

involved in cell

movement

*microtubules-hollow tubes of protein, can serve as “tracks” along which organelles move

*microfilaments-long, thin fibers that function in the movement & support of cells

E. Organelles in the cytoplasmRibosomes -small particles made of RNA &

protein -produce proteins following coded

instructions from the nucleusEndoplasmic Reticulum (ER)- organelle in

which components of the cell membrane are assembled & some proteins

are modified (rough E.R.-have ribosomes attached to the surface)

Golgi Apparatus-enzymes in the

Golgi Apparatus attach

carbohydrates & lipids to proteins

Lysosomes-small organelles filled

with enzymes that break down lipids,

carbohydrates, & proteins

from food into particles

that can be used by the

rest of the cell (also break

down organelles)

Vacuoles- sac-like structures that store materials like water, salts, proteins & carbohydrates

Chloroplast-found in plants-use energy from sunlight to make

energy rich molecules in a process known as photosynthesis

-have a double membrane

Mitochondria- use energy from food to make high energy compounds that the cell can use to power growth, development, & movement

-have a double

membrane

-found in nearly all

eukaryotic cells

F. Organelle DNA

• Chloroplasts and mitochondria contain some of their own genetic information in the form of DNA

• These small DNA molecules contain information that is essential for them to function

• Could be prokaryotic cells that were engulfed by eukaryotic cells & formed a symbiotic relationship

CENTRIOLES

Appear during cell division to guide chromosomes apart

Made up of microtubulesOnly seen in animal cells

CENTRIOLES/MITOTIC SPINDLE

Made of MICROTUBULES (Tubulin)

Image from: http://www.coleharbourhigh.ednet.ns.ca/library/organelle_worksheet.htm

FLAGELLA & CILIA

Made ofPROTEINS called MICROTUBULES

(9 + 2 arrangement)

Image from: http://www.stchs.org/science/courses/sbioa/metenergy/flagella.jpg

FLAGELLA

Help in cell movement

Very few and long in length

CILIA

Move cell itselfAnd substances past the cell. Very many and short in length

Animation from: http://web.jjay.cuny.edu/~acarpi/NSC/13-cells.htm

Section 3: Movement through the Membrane

• The cell membrane regulates what enters & leaves the cell & also provides protection & support (figure 7-15)

-lipid bilayer–a double layered membrane formed when certain kinds of lipids are dissolved in water

-embedded proteins-forms channels & pumps that help move materials across the membrane

-carbohydrate chains-attach to proteins & aids in chemical identification to allow cells to ID one another

Cell Membrane

Diffusion: tendency of molecules to move from an area of high concentration to an area of lower concentration to reach equilibrium (figure 7-16)

-causes many substances to move across the cell membrane but does not require the cell to use energy

-concentration=mass of solute/volume of solution

Osmosis: diffusion of water through a selectively permeable membrane (fig 7-17)

-selectively permeable= some substances can pass through but others cannot

-isotonic-same strength solution on both sides

-hypertonic-above strength inside (water leaves)

-hypotonic-below strength inside (water enters)

• Osmosis exerts pressure known as osmotic pressure on the hypertonic side of the selectively permeable membrane.

-osmotic pressure can cause a cell to shrink or burst (figure 7-18)

Facilitated Diffusion: the process of protein channels allowing a pathway for certain molecules to cross the membrane (figure 7-19)

-100’s of different protein channels have been found that allow ions, sugars & salts to cross the membrane

Active Transport: requires energy to move molecules across a cell membrane against a concentration difference. The materials move from an area of lower concentration to an area of higher concentration (figure 7-20)-often compared to a pump

Endocytosis: the

process of taking large

particles into the cell by

means of infoldings or

pockets of the cell

membrane that form

vacuoles

Phagocytosis: process of taking large particles into the cell by endocytosis. Extensions of the cytoplasm surround & engulf the large particles.

Exocytosis: membrane of the vacuole surrounding material fuses with the cell membrane, forcing the contents out of the cell

Review

1. What processes are made possible by the cell membrane?

2. How does diffusion affect cells?3. Describe how water moves during

osmosis.4. What is the basic structure of a cell

membrane?5. How does active transport differ from

diffusion?