Chapter 4

Cell Structure and Function

Do Now

What is the common structure that makes up every living thing?

What instrument do you need to see them?

The Discovery of the Cell

• Advances in technology led to the discovery of the cell: INVENTION OF MICROSCOPE.

1665: Robert Hooke• English scientist that

used an early compound microscope to look at cork.

• Noticed empty “chambers” or “boxes” in cork and named them “cells.”

• He named them cells because they reminded him of the small rooms where monks lived

• He was looking at the remains of dead plant cells

Anton van Leeuwenhoek• This Dutch

scientist was the first person to observe living cells

• Used single-lens microscope to observe pond water.

• Observed microorganisms.

Making of the Cell Theory• Proposed by 3 German scientists:

– In 1838, botanist Matthias Schleiden concluded that “All plants are made of cells”

– In 1839, zoologist Theodor Schwann concluded that “All animals are made of cells”– In 1855, physician Rudolf Virchow

concluded that “New cells are produced only from the division

of existing cells”

The proposals made by these 3 men have been continually confirmed by other biologists and make up the:

Cell Theory

1. All living things are composed of one or more cells.

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

3. Cells come only from the reproduction of existing cells.

CELL DIVERSITY - not all cells are alike

Size: • 2m (nerve cells in giraffe’s leg) to

0.2um (bacteria)• Cell is limited in size by its surface

area to volume ratio• Food and oxygen must enter through

its surface• As a cell grows large, its surface area

becomes too small to maintain its life functions

CELL DIVERSITYShape – cube, square, round, irregularForm reflects function:

Nerve cell – reaches out to send impulsesSkin cell – flat and covers bodyWhite blood cell – can change shape

Cell activity

• Structure and Function of Cells Worksheet

• Finish for homework

Do Now

• Who named “cells” after looking at cork cells?

• Who first examined living cells?• What are the 3 points of the cell

theory?

2 Types of Cells

–Prokaryotes – lack:• nucleus - for containing genetic

material• membrane bound organelles - cell

compartments that carry out specific cell functions – like our organs

–Eukaryotes – contain:• a nucleus • membrane bound organelles

Prokaryotes

• Smaller and simpler than eukaryotic cells.

• Genetic material is not contained in a nucleus.

• No organelles• Bacteria• First cells on earth

– prokaryotic heterotrophs

Eukaryotes• Larger and more

complex than prokaryotes.

• Contain a nucleus with DNA.

• Organelles• Plants, animals,

fungi, and protists.

Do Now

• Name the 2 basic differences between prokaryotic and eukaryotic cells.

• Give an example of each type of cell.

Cell Membrane

• All cells have a cell membrane:–A thin membrane that surrounds

the whole cell–Selectively permeable – it

regulates what enters the cell (nutrients) and leaves the cell (wastes)

–Provides protection and support–Made of lipids and proteins

Cell Membrane

• Phospholipid bilayer: double-layered sheet of lipids–Hydrophilic phosphate heads

love water and are directed outward toward the watery environments

–Hydrophobic lipid tails are afraid of water and are directed inward toward each other to get away from the watery environments

Cell Membrane

–Gives cell flexible structure

–Forms strong barrier between the cell and surroundings

Membrane Proteins

• Most cell membranes contain 2 types of proteins:– Peripheral proteins – located on

both the interior and exterior surface of the cell membrane

– Integral proteins – embedded in the lipid bilayer - can extend all the way across from outside of the cell to inside of the cell

Membrane Proteins• Act as gates, channels, or pores

– Form channels and pumps that help move material across membrane

• Carbohydrates are sometimes attached to membrane proteins as cell markers– Carbs act as chemical ID cards,

allowing cells to identify one another

Fluid Mosaic Model• Scientists used to think that the cell

membrane was static – didn’t move or change

• New technology tells us that the lipid bilayer behaves more like a liquid (fluid) than a solid

• Lipids and proteins can move around laterally and their pattern (mosaic) is always changing

Do Now

• What is the term that describes the gatekeeper duty of the cell membrane?

• What is the cell membrane made of?

• What 2 types of proteins are in the cell membrane?

Eukaryotic Cells• Divided into two major parts:

–Nucleus–Cytoplasmwith organelles

Organelles• Cytoplasm – area between the

nucleus and cell membrane which contains organelles

• Organelles are membrane bound structures that perform a specific function

• Organelles are bathed in a gelatin-like fluid called the cytosol that contains salts, minerals and organic compounds

Mitochondria•Convert chemical energy stored in food compounds that the cell can use for energy (ATP)

•Enclosed by two membranes:

•Inner membrane has folds (cristae) to increase surface area for chemical reactions

Mitochondria• Mitochondria are numerous in cells

with high energy requirements (muscles)

• Mitochondria have their own DNA and new ones only arise through growth and division

• There is a theory that they developed from prokaryotic cells living inside eukaryotic cells (symbiosis)

Ribosomes•Small particles of RNA and protein – no membrane

•Proteins are assembled at ribosomes:

•Some are free in the cytoplasm (proteins used inside of cell)•Some are attached to endoplasmic reticulum (proteins for use outside of cell)

Endoplasmic Reticulum (ER)

•A system of membranous tubes and sacs

•Functions as an intracellular highway

•Molecules can be moved from one part of cell to another

Rough ER• Rough ER:

– covered with ribosomes – found in cells which produce a lot of proteins to be exported from cell

Smooth ER

• Smooth ER:– not covered with ribosomes– Found in gland cells that produce steroids and liver cells that breakdown toxic substances

Cell Activity

• Cell Structure and Function worksheet

Do Now

• What is the function of the mitochondria?

• What is the function of the ribosome?• What are the 2 types of ER?

Golgi Apparatus•Stack of flattened sacs

•Proteins move from ER to Golgi

•Golgi customizes and ships proteins to final destinations

•Modifies, sorts, and packages materials from ER for:

•Storage in cell•Secretion outside of cell

Lysosomes – not common in plant cells

•Small, round organelles filled with hydrolytic enzymes (suicide sacs)

•Digestion of lipids, proteins, carbs, DNA & RNA in the cell

•Digests old organelles, viruses and bacteria

•May selectively destroy tissue to shape bodies of animals during development

Cytoskeleton

•Supportnetwork of protein strands

•Helps:•maintain cell shape•organelle movement

Microfilaments – part of cytoskeleton

Smaller strands made of actin protein

Produce a framework that supports the cell

Helps cells move and muscle cells to contract

Microtubules – part of cytoskeleton

•Larger strands made of tubulin proteins

•Maintain cell shape

•Form cilia and flagella

•Important in cell division: •form spindle fibers•form centrioles

Cilia and Flagella

• Hair-like organelles that extend fro surface of cell and assist in movement

• Cilia – short and present in large numbers– Microorganisms – movement of cilia propels

them through water– Respiratory tract – trap particles from air and

sweep them back to your throat to be swallowed

• Flagella – long and less numerous– Sperm cells – whip-like motion can propel

cells

Nucleus•Contains nearly all cell DNA in form of chromatin (hereditary information)

•When cell is about to divide, chromatin coils up and becomes chromosomes

•Surrounded by nuclear envelope

•lined with pores•RNA, proteins, and other molecules can move into cell

Nucleus Also contains the nucleolus:

Site where ribosomes are synthesized

Do Now

• What is the function of the Golgi apparatus?

• What are the parts of the cytoskeleton?

• What is the function of the nucleus?

Plant cells

• May contain 3 additional structures important to plant cell function:

–Cell Walls

–Vacuoles

–Plastids

Cell WallsPresent in plants, algae, fungi, and many prokaryotes

Lie outside the cell membrane

Pores let water, oxygen, and carbon dioxide pass through easily

Cell Walls

• Provide support and protection for cell• Made from carbs and protein.

– Cellulose –carbohydrate fiber– Principal component of wood and paper

Vacuole•Fluid filled organelles that store enzymes and wastes

•Plants have a single, large, central vacuole used for support

•Helps control water content and maintain homeostasis

Plastids•Surrounded by two membranes

•Can contain pigments that capture energy from sunlight

•Chloroplasts have a system of flattened membranous sacs called thylakoids

•Chloroplasts contain chlorophyll that converts the sun’s energy into chemical energy via photosynthesis

Do Now

• Name the 3 parts of a plant cell that animal cells don’t have.

• What advantage do chloroplasts give to plants?

Multicellular Organization

• Unicellular organisms – one cell carries out all functions of life

• Multicellular organisms – cells are specialized to perform one or a few functions– Specialization means that cells depend

on other cells for survival

Levels of Organization• Cells: basic units of organization• Tissues: similar cells grouped into

units to carry out specific functions (epithelial tissue)

• Organs: several types of tissues that work together to perform a function (stomach)

• Organ systems: group of organs that work together to perform a set of related tasks (digestive system)

Evolution of Multicellular Organization

• Fossil evidence suggests that the first cells on earth were prokaryotes (like bacteria)

• They couldn’t synthesize their own nutrients

• Depended on organic nutrients in environment

• Began to compete for limited resources• Cells with adaptations arose –

unicellular eukaryotes

Colonial Organizations

• Some of the unicellular eukaryotes began to live in groups or colonies

• Some of the cells may have specialized in performing certain functions

• Colonial Organisms – a collection of genetically identical cells that live together in a closely connected group

• Volvox – example of colonial organism

Volvox• Hollow sphere containing 500 – 60,000 cells

• Each cell maintains its own existence, but many perform specific functions that benefit the whole colony– Outer cells use flagella

to propel the colony– Some cells are

specialized for reproduction

Colonial Organizations• May be a link between unicellular

organisms and true multicellular organisms

• They lack tissues and organs, but do have specialized cells

• This may be how multicellular organisms evolved:– Cells became more specialized– Less capable of living apart