Cell Structure and Function

Chapter 4

Chapter 4 Vocabulary• Cell• Cell theory • Plasma membrane• Cytoplasm• Nucleus• Prokaryote• Eukaryote• Phospholipid bilayer• Nuclear envelope• Nucleolus• Ribosome

• Mitochondrion• Endoplasmic reticulum• Golgi apparatus• Lysosome• Microtubule• Microfilament• Cilium• Centriole• Cell wall• Central vacuole• Plastid

The History of Cell Biology

The Discovery of Cells

• All living things are made up of one or more cells

• Cell – the simplest unit that can perform all of life’s processes

• The use of microscopes allowed scientists to see cells for the first time

The Discovery of Cells

• Hooke– English scientist, 1665– Early light microscope– Observed cork cells– Coined the term “cell”

• Leeuwenhoek– First to observe living cells– “animalcules” = protists

The Cell Theory

• Came about 150 years after Hooke and Leeuwenhoek• Developed by scientists Schleiden, Schwann, and

Virchow• CELL THEORY:

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

2. Cells are the basic units of structure and function in an organism.

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

Self Quiz

1. What are the three parts of cell theory?2. Who discovered the first cells? What were

they?3. What invention was important in the

discovery of cells?

Introduction to Cells

Cell Diversity

• Diverse in shape, size, organization • A cell’s function influences its physical features

Cell Shape

• Cell shape reflects function

Cell Size

• Surface area – to – volume ratio– Limits the size of the cell– Relationship of the cell’s outer surface area to its

volume

Cell Size

• Materials needed by cell and waste produced pass in and out of the surface

• Surface area must be big enough to allow materials to enter and leave cell quickly

• This is why most cells are microscopic

Two Types of Cells• Prokaryotes – lack a nucleus and membrane-

bound organelles– Ex. Bacteria

• Eukaryotes – have a nucleus and membrane-bound organelles– Ex. Plants, Birds, Mammals

Prokaryotic Cell

Eukaryotic Cell

Prokaryotes

• Lack a nucleus• Genetic information is DNA• Genetic information

concentrated in a part of the cell called a nucleoid

Eukaryotes

• Have a nucleus• Have membrane-bound

organelles – Organelles – well-

defined, intracellular bodies that perform specific functions for the cell

• Generally larger than prokaryotes

Cellular Organization

• Cells are grouped based on their function• Groups of cells took specific roles

Cellular Organization

• Tissue – a group of similar cells and their products that carry out a specific function

• Organ – groups of tissues that perform a particular job in an organism

• Organ system – a group of organs that accomplish related tasks

CELLS

Self Quiz

1. What is the difference between prokaryotes and eukaryotes?

2. What types of organisms are prokaryotes?3. What types of organisms are eukaryotes? 4. Why are cells so small?

Basic Parts of a Cell

• All cells have:– An outer boundary• Plasma membrane

– Inner substance• Cytoplasm

– Control region• Nucleus (in eukaryotes)

Plasma Membrane (Cell Membrane)• Only allows certain

molecules to enter or leave the cell

• Separates internal metabolic reactions from the external environment

• Allows cells to excrete waste• Cell can interact with

environment

Plasma Membrane (Cell Membrane)

• Membrane lipids• Membrane proteins• Fluid mosaic model

Membrane Lipids• Cell membrane made

primarily of phospholipids

• Phospholipids– Hydrophilic phosphate

head– Hydrophobic fatty acid

tails• Called the phospholipid

bilayer

Membrane Proteins• Cell membrane contains proteins• Integral proteins – embedded • Peripheral proteins – lie only on one side of the

membrane

Membrane Proteins

• Play important roles in transporting molecules into the cell.– Channels– Pores– Transport sites– Chemical messenger attachment site

Fluid Mosaic Model

• Phospholipid bilayer behaves more like a fluid than a solid.

• Can move like a boat on the ocean• Pattern “mosaic” constantly changes

Self Quiz

• What is the role of the cell membrane?• What is a phospholipid composed of?• How does the phospholipid bilayer work?

Nucleus

• Houses and protects the cell’s genetic information– DNA

• Site where DNA is transcribed to RNA

Nucleus

• Nuclear envelope – double membrane that surrounds the nucleus.

• Nuclear pores – provide passageways for RNA and other materials

Nucleus

• Nucleolus – a denser area of the nucleus• The site where DNA is concentrated when

making ribosomal RNA– Ribosomes – organelles made of protein and RNA

that direct protein synthesis in the cytoplasm

Mitochondria

• Mitochondria – tiny organelles that transfer energy from organic molecules to ATP– ATP powers most cell chemical reactions– “powerhouse” of the cell

• Inner and outer phospholipid membrane– Folds in the inner membrane called cristae

Ribosomes

• Responsible for building protein• Made up of protein and RNA molecules• Made up of subunits– Large subunit– Small subunit

Self Quiz

• What is the role of the nucleus?• Why are mitochondria so important?• Why is it important for mitochondria to have

many folds?• What is the structure of a ribosome? What do

they do?

Activity

• Why is your organelle the best?• Come up with an argument for why your

organelle would be the most important in the cell.– What does it do?– Why is it important?– Could the cell function without it?

Endoplasmic Reticulum (ER)

• System of membranous tubes and sacs called cisternae

• Functions as an intercellular highway• Allows molecules to move from one part of

the cell to another• Two types:– Rough ER– Smooth ER

Rough ER

• System of interconnected, flattened sacs• Covered with ribosomes• Produces phospholipids and proteins– Ex. Digestive enzymes

Smooth ER

• Has smooth appearance• Lacks ribosomes• Builds lipids, such as cholesterol• Forms an interconnected network with the

rough ER

Golgi Apparatus

• System of flattened, membranous sacs• Vesicles move through the Golgi• Vesicle contents is modified• Proteins get “address labels” and get directed

to other parts of the cell

Vesicles

• Small, spherically shaped sacs• Several types present in the cell• Perform various roles• Classified by their content

Types of Vesicles

• Lysosomes• Peroxisomes• Glyoxysomes• Endosomes• Food vacuoles• Contractile vacuoles

VesiclesVesicle Type Functions

Lysosomes Contain digestive enzymes; break down unused large molecules

Peroxisomes Neutralize free radicals; break down toxins in the body and kill bacteria

Glyoxysomes Break down stored fats in seeds

Endosomes Engulf material to take to the lysosomes to digest

Food vacuoles Store nutrients

Contractile vacuoles Contract to expel excess water from a cell

Cytoskeleton

• Network of thin tubes and filaments in cytosol• Gives shape to cell– Like tent poles

• Acts as tracks for movement around cell• Composed of– Microtubules– Microfilaments– Intermediate filaments

Microtubules

• Hollow tubes• Made of protein called tubulin• Radiate out from centrosome• Hold organelles in place• Maintain cell shape

Microfilaments

• Long threads of protein called actin• Contribute to cell movement– Ex. Contraction of muscle cells

Cilia and Flagella

• Hair-like structures that extend from the surface of the cell

• Assist in movement• Cilia are short and numerous• Flagella are longer and less common

Self Quiz

• What are the different types of vesicles? What do they do?

• What is the difference between the rough ER and smooth ER?

• What roles do microtubules and microfilaments play in the cell?

• What is the role of the Golgi apparatus?

Plant Cells

Plant Cells

• Plant cells have some structures not found in animal cells– Cell wall– Central vacuole– Plastids

Cell Wall

• Cell wall – a rigid layer that lies outside the cell membrane

• Contains cellulose, a carbohydrate• Plants have primary and sometimes secondary

cell walls

Central Vacuole

• Central vacuole – a large fluid filled organelle that stores water, enzymes, metabolic wastes, and other materials

• A large reservoir• Can make up 90% of the plant cell’s volume

Plastids

• Plastids – organelles surrounded by a double membrane– Contain their own DNA (like mitochondria)– Several types• Chloroplasts• Chromoplasts• Leucoplasts

Chloroplasts

• Use light energy to make carbohydrates from carbon dioxide and water

• Contains thylakoids, flattened membranous sacs

• Thylakoids contain chlorophyll– Chlorophyll – absorbs light and captures light

energy for the cell

control region

Eukaryotic Cells

include

Both of which have

Which haveCell wall

Nucleus