Cell Structures

A Tour of the Cell

Overview: The Fundamental Units of Life

• All organisms are made of cells

• Cell: collection of living matter enclosed by a barrier – Basic unit of all forms of life

Prokaryotic vs. Eukaryotic

• The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic

• Prokaryotic: bacteria

• Eukaryotic: protists, fungi, animals, and plants

Comparing Prokaryotic and Eukaryotic Cells

• Basic features of all cells: – Plasma (cell) membrane– Semifluid substance called cytoplasm

(cytosol)– Chromosomes (carry genes)– Ribosomes (make proteins)

• Prokaryotic cells are characterized by:– A cell wall and cell membrane

– No nucleus

– Cytoplasm bound by the cell membrane

– DNA in the cytoplasm

– No membrane-enclosed organelles

• Eukaryotic cells are characterized by:– DNA in a nucleus bound by a membrane

• The membrane is the nuclear membrane (envelope)

– Membrane-bound organelles– Cytoplasm between the cell membrane and

nucleus

• Eukaryotic cells are generally much larger than prokaryotic cells

• The cell membrane is a phospholipid bilayer

– It is a selective barrier

• Only allows certain things into and out of the cell

– Oxygen, nutrients, and waste

• A eukaryotic cell has internal membranes that separate the cell into organelles– Only plant cell organelles will be discussed– Organelle: specialized structure that performs important

cellular functions

Cytoplasm (Cytosol)

• Jelly-like fluid and materials containing everything between the cell membrane and nucleus

• Including organelles• Where most of the cell’s work is done

The Nucleus

• The nucleus is the control center of the cell – Usually the easiest organelle to see under the microscope

– Contains most of the cell’s DNA• Instructions (blueprints) for making proteins and other

molecules

• The nuclear envelope encloses the nucleus, separating it from the cytoplasm– The nuclear membrane is a double membrane

• Thousands of pores within the membrane allows for passage of materials in and out to receive messages and send instructions

• The nucleolus is the small dense (dark) area within the nucleus– Where ribosome production occurs

• Ribosomes then move into the cytoplasm

Ribosomes• Ribosomes are made of RNA and protein• Ribosomes produce proteins in two areas:

– In the cytoplasm (free ribosomes)– Attached to the outside of the endoplasmic reticulum

(bound ribosomes)

• Produce proteins by following instructions (orders) sent from the nucleus

The Endoplasmic Reticulum

• The endoplasmic reticulum (ER) is an internal membrane system (made of membranes)

• The ER membrane connects to the nuclear envelope

• Used to produce and transport materials such as proteins

• There are two distinct regions of the ER:– Smooth ER, which lacks

ribosomes– Rough ER, with ribosomes on its

surface

Functions of Rough ER

• The rough ER– Has bound ribosomes

• Proteins made (synthesized) in ribosomes are moved to the ER to be modified (changed or added to)

– Then these proteins are released into the cell or exported out of the cell

– Is a membrane factory for the cell• Makes many proteins found on the cell membrane

Functions of Smooth ER

• The smooth ER– Synthesizes (produces) lipid components of the

cell membrane• Sometimes stores lipids after making them

– Detoxifies drugs• Makes poisons no longer poisonous (neutralizes)

• The Golgi apparatus is made of membranes– Look like flattened stacks of membranes

• Functions of the Golgi apparatus:– Modifies, sorts, and packages products of the ER

• Customizes proteins and other materials• Stores for later use• Packages and ships products outside the cell

The Golgi Apparatus

Vacuoles

• A plant cell may have one or more vacuoles

• Vacuoles hold organic compounds (salts, proteins, and carbohydrates) as well as water for later use– Makes it possible for

plants to support leaves and flowers (heavy structures)

Chloroplasts and Mitochondria

• Chloroplasts and mitochondria– Have a double membrane

• Two membranes make up the organelles

– Have proteins made by free ribosomes– Contain their own DNA

Chloroplasts• Chloroplasts, found in plants and are the sites of

photosynthesis– Captures energy from sunlight and converts it into

chemical energy (food)– Solar power plant

• Contain large stacks of membranes containing chlorophyll– Chlorophyll is the green pigment that function in

photosynthesis by capturing light energy• Chloroplasts are found in leaves and other green organs of

plants and in algae

Mitochondria• Mitochondria convert the chemical energy in

food into compounds the cells can use– The site of cellular respiration, a metabolic process

that produces ATP• ATP is the molecule cell’s use for energy (to do their work)

• Mitochondria are in nearly all eukaryotic cells– Inherited from your mother through the egg

(ovum)

Cell Walls of Plants• The cell wall is an extracellular structure that

distinguishes plant cells from animal cells

– Extracellular: outside the cell membrane

• Also found in algae, fungi, and many prokaryotes

• Porous (contains mini holes) to allow for water, oxygen, carbond dioxide, and small molecules to pass through

• The cell wall in made within the cell itself

• The cell wall helps protect the plant cell by providing extra shape and support for the cell

– Make up of cellulose

• Cellulose is a carbohydrate polymer that strengthens the plant cell wall and only found in plants

– Not the same thing as cellulite (found in animals)

– Cellulose is the primary component of wood and paper

– Prevents excessive uptake of water

• What happens in animal cells when too much water is taken into the cell?

Lab

• Wednesday– We will meet as normal to discuss the

experiment• The experiment will explore how the plant’s cell

wall helps maintain shape when under harsh conditions.

• This experiment uses the microscope so review how to use the microscope from your notes of the first 9 weeks.