Cell Structure and Function

Cell Structure and

Function- Chapter 4

Life is Cellular

•Key Concepts–What is the cell theory?–What are the characteristics of prokaryotes and eukaryotes?

Cell Theory

• First microscope wasn’t invented until the early 1600’s. (Leeuwenhock, Hooke)

• By the 1800’s all the discoveries made by all scientists using the microscope were summarized in the Cell Theory.

The Cell Theory States the Following:

• All living things are composed of cells

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

• New cells are produced from existing cells.

Basic Cell Structure

• Structures common to MOST cells– Cell Membrane - that surrounds the cell

– Nucleus - containing the cell’s genetic material

– Cytoplasm - the material inside the cell membrane but outside the nucleus. Contains organelles.

PRO versus EU

• Biologists divide cells into two categories:– Eukaryotes– Prokaryotes

• The cells of eukaryotes have a nucleus, but the cells of prokaryotes do not

Prokaryotes

• Smaller and simpler but carry out all activities associated with life.

• Have cell membrane and cytoplasm but do not contain nuclei (plural of nucleus)

• Example: Bacteria

Eukaryotes

• Have a nucleus, cell membrane and cytoplasm

• Also have organelles that are specialized structures that perform important cellular functions.

Cell Structures

• Key Concept: – What are the functions of the major

cell structures?

Cell Wall

• Main function is to provide support and protection for the cell.

• Found in plants, fungi and prokaryotes

• Made of carbohydrate and protein.

Nucleus

• Controller - directs most cell processes and contains the hereditary information of DNA

• Contains structures called chromosomes which are made of DNA

• Most contain another organelle: the nucleolus which assembles ribosomes

The Nucleus

Chromatin

Nucleolus Nuclear pore

Nuclear envelope

Cytoskeleton•Network of protein filaments that helps the

cell to maintain its shape.

•Also involved with movement.

Organelles of the Cytoplasm

• Ribosomes: site of protein synthesis

• Endoplasmic Reticulum (ER): components of the cell membrane are assembled here and some proteins are modified. Two types: – Rough (studded with ribosomes and produce

proteins)– Smooth( contains enzymes and may produce

lipids)

ribosomes

•Golgi Apparatus: –a stack of membranes that attach carbohydrates and lipids to proteins.–The modified proteins are then sent to their final destination.

• Lysosomes: – small organelles filled with enzymes that

digest cell “food” into particles that can be used to build structures for the cell.

• Vacuoles: – saclike structures used for storage in

cells. In plants they are very large.

•Chloroplasts:–Found in plants– Use energy from the sun to make energy-rich food molecules through photosynthesis.

•Mitochondria: –organelles that release energy from stored food molecules into high-energy compounds that the cell can use for growth, development, and movement.–Found in all eukaryotic cells.

The Factory Analogy

•If the cell is like a factory, then what jobs would each of the organelles do?

Comparing Cells

•Eukaryote •Prokaryote

Unique Features of Plant Cells• Three additional structures:

– Cell wall– Central vacuole– Plastids such as choloplasts.

Cell Wall• It is a rigid layer outside of the cell

membrane

• Composed of cellulose

Central Vacuole• Large fluid filled organelle the stores

water, enzymes, metabolic wastes and other materials

• Make up 90% of plant cell volume

• When water is plentiful, the central vacuole fills up and the plant stands upright. In periods of drought, the plant wilts.

• Other vacuoles in plants store toxic materials or pigments.

Plastids• Organelles like mitochondria that are

surrounded by a double membrane and contain own DNA

• Chloroplasts– Site of photosynthesis, contains

chlorophyll. DNA similar to bacteria—endosymbiosis

Chromoplasts: contain colorful pigments

Other

amyloplasts store starch

What Are The Differences Between

Animal and Plant Cells?

• Let’s practice by making cells.

• http://www.wiley.com/legacy/college/boyer/0470003790/animations/cell_structure/cell_structure.htm

Movement Through the Membrane

• Cell Membrane - regulates what enters and leaves the cell and also provides protection and support.

• Made of a double-layered sheet of lipids.• http://www.youtube.com/watch?

v=vh5dhjXzbXchttp://www.susanahalpine.com/anim/Life/

memb.htm

Cell Membrane Structure

Lipids• Lipids are large, nonpolar organic

molecules.

• They do not dissolve in water

• Lipids include triglycerides, phospholipids, steroids, waxes and pigments.

• Lipids are made of carbon, hydrogen, and oxygen molecules

Classes of Lipids

• Fatty acids– Are unbranched carbon chains that make

up most lipids.– One end has a polar carboxyl group and is

hydrophilic or attracted to water molecules and the carbon chain is nonpolar or hydrophobic and does not interact with water molecules.

• If the carbon atoms in the fatty acid chain is covalently bonded to four other atoms, the carbon is saturated.

• If the carbon is double bonded in the chain, it is unsaturated.

TriglyceridesTriglycerides are one of the important types of lipids in living organisms.

•composed of three molecules of fatty acid attached to a glycerol molecule.

•Saturated triglycerides are solid at room temperature: butter, fats in meat.

•Unsaturated triglycerides are liquid at room temperature: oils.

Waxes and Steroids• Waxes are a water-proof structural

lipid that form a protective coating on outer surfaces.

• Steroid are rings of carbon atoms with functional groups attached to them. Many hormones such as testosterone are steroids.

Phospholipids• Phospholipids have two rather than

three fatty acids attached to a molecule of glycerol, also a phosphate molecule attached to one of the carbons in the glycerol molecule.

• Not soluble in water, it forms the cell membrane that is the barrier between the inside and outside of the cell.

Homeostasis and Cell Transport• Cell membranes help organisms

maintain homeostasis by controlling what substances may enter or leave cells some substances can cross the cell membrane without any input of energy by the cell in a process known as passive transport

Diffusion

• As molecules move about, they bang into each other. They move from where they are more concentrated to where they are less concentrated through diffusion.

• Diffusion causes many substances to move across the cell membrane.

• http://www.stolaf.edu/people/giannini/biological%20anamations.html

Diffusion Across a Cell Membrane

Osmosis

• It is the diffusion of water through a selectively permeable membrane

• Not all substances can pass through the cell membrane--it is selective!!

• Water will move across a cell membrane until equilibrium is reached.

• http://www.stolaf.edu/people/giannini/biological%20anamations.html

Osmosis

• Cells contain salts, sugars, proteins, and other materials. They are almost always hypertonic (more stuff and less water) to their surroundings. Water wants to diffuse into the cell. http://www.tvdsb.on.ca/westmin/science/Sbi3a1/cells/Osmosis.htm

– In large organisms (you), the cells are bathed in fluids that have the same concentration of materials as the inside of the cell: isotonic

– Other cells and organisms that live in freshwater have various mechanisms for keeping the water out.

• Only a few organisms can survive in water that has a very high concentration of salts or other solutes compared to the concentration inside the cell.

• This is called hypertonic.

• In the space on your paper, draw the three conditions we have just discussed:Hypotonic, Isotonic, Hypertonic.

Hypotonic Isotonic Hypertonic

The Effects of Osmosis on Cells

Facilitated Diffusion

• Not all molecules can diffuse across the cell membrane

• Sometimes proteins in the cell membrane “help” or facilitate the movement of certain molecules like glucose.

• The cell uses no energy. It is still diffusion.

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/simple_multiple_choice.html

Ion Channels• Another type of passive transport.

• Ions can’t move through the cell membrane.

• Ca2+, Na+, K+, Cl- are important ions in living organisms that are transported in this manner.

• Each ion channel is specific to a particular type of ion.

Facilitated Diffusion

Active Transport

• Used to move material across the cell membrane when the concentration of the substance is already higher in the cell than outside of the cell

• Needs energy (active)• Example: Sodium-potassium pump.http://www.stolaf.edu/people/giannini/

biological%20anamations.htmlhttp://www.northland.cc.mn.us/biology/

BIOLOGY1111/animations/active1.swf

Active Transport

• Really big stuff move by – Endocytosis: making a fold or pocket in the cell

membrane creating a vacuole.– Phagocytosis: changing the shape of the cell

membrane to surround a food particle.– Exocytosis: surrounding material IN the cell

and sending it out. Opposite of endocytosis.

• http://www.stolaf.edu/people/giannini/biological%20anamations.html