Chapter 7Cell Structure & Function

7-1: Life is Cellular

»OBJECTIVES:• What is the cell theory?

• What are the characteristics of prokaryotes and eukaryotes?

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• There is a common structure that makes up every living thing - the cell

The Discovery of the Cell• In 1665, Robert Hooke used a microscope and

saw chamber in cork that he called cells• Anton van Leeuwenhoek also observed tiny

organisms in water• Contributions to the cell theory:

– Schleiden - all plants are made of cells– Schwann - all animals are made of cells– Virchow - new cells could only come from the

division of existing cells• The Cell Theory:

– All living things are composed of cells– Cells are the basic units of structure & function– New cells are produced from existing cells

CORK CELLS

White Boards• Who was the first scientists to see

living cells?

White Boards• Which scientist determined that all

animals are made of cells?

White Boards• The cell theory says:

– All living things are composed of cells– New cells are produced from existing

cells– Cells are the basic units of _____?_____

Exploring the Cell

• Light microscopes are limited in detail (resolution) because light is easily scattered as it passes through air

• Electron microscopes (TEM’s and SEM’s) can view things 1000x smaller than light microscopes

• Scanning probe microscopes can operate in ordinary air and can even show samples in solution (DNA, protein, and other biomolecules)

SEM

IMAGES

Prokaryotes and Eukaryotes

• All cells have two things in common– Surrounded by a barrier (membrane)– Contain DNA

• The nucleus is a membrane-enclosed structure that contains the cell’s genetic material in the form of DNA

• Prokaryotic cells have no nucleus

• Eukaryotic cells have a nucleus

Prokaryotes and Eukaryotes

Prokaryotes and Eukaryotes

Prokaryotes Eukaryotes

Nucleus NO YES

Size Generally Smaller

Generally Larger

Specialized Structures

Not Usually

YES

Number of Cells

Unicellular Unicellular or Multicellular

White Boards• What two features do all cells

share?

White Boards• Which type of organism has cells

that contain a nucleus?

PROKARYOTIC or EUKARYOTIC

7-1 Section Assessment

1. What three statements describe the cell theory?

2. What are the differences between prokaryotic cells and eukaryotic cells?

3. Compare the processes used to create a TEM and an SEM.

4. What structures do all cells have?

5. How did the invention of the microscope help the cell theory?

7-2: Eukaryotic Cell Structure

• What are the functions of the major cell structures?

Comparing the Cell to a Factory

• At first, cells look impossibly complex, but patterns eventually emerge

• Many structures are common to eukaryotic cells

• These structures act as specialized organs and are called organelles

• Eukaryotic cells are divided into two parts: The nucleus and the cytoplasm

White Boards• Eukaryotic cells are divided into

two parts: the ________ and the ________.

Nucleus• The nucleus is the control center• The nucleus contains nearly all the cell’s DNA:

Coded instructions for making proteins and other molecules

• It is surrounded by a nuclear envelope which has pores to let materials in and out

• Chromatin is granular material in the nucleus which is made of DNA bound to protein

• Chromatin condenses to form chromosomes when the cell divides

• The dark region in the nucleus is the nucleolus: The location of ribosome construction

White Boards• ________ is made of DNA bound

to protein.

White Boards• When a cell divides, chromatin

condenses to form ________.

Ribosomes

• Proteins are assembled on ribosomes

• Ribosomes are small particles of RNA and protein and are found throughout the cytoplasm

• They produce proteins by following coded instructions that come from the nucleus

White Boards• Where do the instructions for

making proteins come from?

White Boards• Proteins can be found throughout

the ________ and are sometimes attached to the ________.

Endoplasmic Reticulum

• The endoplasmic reticulum (ER) is the site where lipid components of the cell membrane are assembled, along with proteins and other materials that are exported from the cell

• Rough ER is covered with ribosomes and is involved in the synthesis of proteins

• Smooth ER does not contain ribosomes and contains collections of enzymes that perform specialized tasks (synthesis of lipids, detoxification, etc.)

White Boards• Rough ER is involved with the

synthesis of ________.

Golgi Apparatus

• The function of the golgi apparatus is to modify, sort, and package proteins and other materials from the ER for storage in the cell or secretion outside the cell

• The golgi ships proteins to their final destinations throughout the cell or outside of the cell

Lysosomes

• Lysosomes are small organelles filled with enzymes

• Lysosomes digest (break down) lipids, carbohydrates, and proteins into small molecules that can be used by the rest of the cell

• Lysosomes also break down unuseful organelles and other “junk” in the cell

Vacuoles

• Vacuoles are saclike structures used for storage of materials such as water, salts, proteins, and carbohydrates

• Plant cells have a large central vacuole used for support

• Vacuoles can also be found in some single-celled organisms and some animals

Mitochondria & Chloroplasts• Mitochondria are organelles that convert the chemical

energy stored in food into compounds that are more convenient for the cell to use

• Nearly all mitochondria in humans come from the cytoplasm of the mother’s egg cell

• Chloroplasts are organelles that capture energy from sunlight and convert it into chemical energy in a process called photosynthesis

• Chloroplasts and mitochondria contain their own DNA

• Lyn Margulis developed the endosymbiotic theory: Prokaryotic ancestors of mitochondria and chloroplasts developed symbiotic relationships with early eukaryotes

White Boards• Organelles that capture energy from

sunlight and convert it to chemical energy are called ________.

Cytoskeleton• The cytoskeleton is a network of protein filaments

that help the cell to maintain its shape• The cytoskeleton is also involved in movement• Microfilaments are threadlike structures made of

actin that:– Support the cell– Assist with movement

• Microtubules are hollow structures made of proteins called tubulins that:– Maintain shape– Form centrioles during cell division (Animal cells only)– Form cilia and flagella

7-2 Section Assessment1. Describe the functions of the endoplasmic

reticulum, Golgi apparatus, chloroplast, and mitochondrion.

2. Describe the role of the nucleus in the cell.

3. What are two functions of the cytoskeleton?

4. How is a cell like a factory?

5. You examine an unknown cell under the microscope and discover the cell contains chloroplasts. What type of organism could you infer that the cell came from?

7-3: Cell Boundaries

• Cell membrane: thin, flexible barrier• Cell Wall: Strong supporting layer around the

membrane of some cells

• What are the main functions of the cell membrane and the cell wall?

• What happens during diffusion?• What is osmosis?

Cell Membrane• The cell membrane regulates what enters and

leaves the cell and also provides protection and support

• Composed of a lipid bilayer with embedded protein molecules and carbohydrates attached to some of the proteins

• Often described as a mosaic• The proteins form channels and pumps to move

materials• The carbohydrates act like chemical

identification cards

White Boards• The cell membrane is composed of

a ________ ________ with embedded protein molecules and carbohydrates attached to some of the proteins.

White Boards• What is the role of the protein in the

cell membrane?

Cell Walls

• Plants, algae, fungi, and many prokaryotes have cell walls

• The main function of the cell wall is to provide support and protection for the cell

• Made from fibers of carbohydrate and protein

• Plant cell walls are made of cellulose: the principal component of wood and paper

White Boards• What types of organisms have cell

walls?

Diffusion Through Cell Boundaries

• The concentration of a solution is the mass of solute in a given volume of a solution (mass/volume)

• Particles in a solution are in constant motion

• The particles tend to spread out from areas of higher concentration to areas of lower concentration: diffusion

• Diffusion occurs until equilibrium is reached

• Diffusion does not require the cell to use energy

White Boards• ___________ is when particles

spread out from areas of high concentration to areas of low concentration.

White Boards• Diffusion occurs until _______ is

reached.

Osmosis• Permeable: substances can pass through• Impermeable: substances cannot pass through• Selectively Permeable: Some can, some can’t• Osmosis is the diffusion of water through a

selectively permeable membrane• Isotonic = same strength, Hypertonic = above

strength, Hypotonic = below strength• Osmosis exerts a pressure known as osmotic

pressure on the hypertonic side of a selectively permeable membrane

• Cells do not fill with water and burst because they are surrounded by isotonic fluids or a cell wall

Diffusion & Osmosis

Diffusion & Osmosis

White Boards• The diffusion of water through a

selectively permeable membrane is called ________.

Facilitated Diffusion

• Cell membranes have protein channels that make it easy for some molecules to cross– Example: red blood cells have a channel that allows

only glucose to cross

• These cell membrane proteins are said to facilitate, or help, diffusion: known as facilitated diffusion

• Facilitated diffusion depends on concentrations for movement and does not require use of the cell’s energy

Active Transport

• Active transport moves materials against the concentration difference and requires energy

• Carried out by transport proteins: “pumps,” or by endocytosis or exocytosis (for large molecules)

• Active transport can concentrate materials even when diffusion tries to move them apart

• Endocytosis takes materials into the cell with infoldings, or “pockets”

• Exocytosis is the process of releasing large amounts of material from the cell

Endocytosis

Exocytosis

Active Transport

Active Transport

7-3 Section Assessment1. Describe the functions of the cell membrane

and cell wall.2. What happens during diffusion?3. Describe how water moves during osmosis.4. What is the basic structure of a cell

membrane?5. What is the difference between phagocytosis

and pinocytosis?6. What id the main way that active transport

differs from diffusion?

7-4:Diversity of Cellular Life

• All living things are:– Composed of cells– Use the same basic chemistry– Follow the same genetic code– Contain the same kinds of organelles

• What is cell specialization?

• What are the four levels of organization in multicellular organisms?

Unicellular Organisms

• A single-celled organism is also called a unicellular organism

• Unicellular organisms do everything you would expect any cell to do:– Grow, respond, use energy, reproduce, etc.

• In terms of their numbers, unicellular organisms dominate life on earth

Multicellular Organisms

• Cells can develop in different ways to perform different tasks: Cell Specialization

• Specialized animal cells:– Red blood cells transport oxygen– Pancreas cells produce protein for digestion– Muscle cells use actin and myosin for movement

• Specialized plant cells:– Stomata are holes in the underside of leaves use for

gas exchange – surrounded by guard cells

Red Blood Cells Pancreas Cells

Muscle Cells

Stomata & Guard Cells

Levels of Organization

• Levels of organization in a multicellular organism are: individual cells, tissues, organs, and organ systems

• TISSUE: Group of similar cells that perform a particular function– Muscle, epithelial, nervous, connective

• ORGAN: Groups of tissues working together

• ORGAN SYSTEM: A group of organs that work together

7-4 Section Assessment

1. In what kinds of organisms is cell specialization a characteristic?

2. List the levels of biological organization in multicellular organisms from most simple to most complex.

3. How are unicellular organisms similar to multicellular organisms?

4. Using what you know about the ways muscles move, predict which organelles would be most common in muscle cells.