CELL STRUCTURECH 6

• Cells are the smallest collection of matter that is alive

• All living things are made of cells

• All cells descend from pre-existing cells

• All cells share several basic features

I. Why are cells so small? A. The surface – to – volume theory

• Metabolic requirements limit cell size• Surface area to volume ratio of a cell is

critical to its metabolic efficiency• Surface area increases by n2 while volume

increases by n3

• Smaller cells have a larger surface area to volume ratio

B. How cells can increase in size without decreasing the SA/V ratio:

• increase their surface area or decrease their volumeoOrganelleso Plant cells : large central vacuole oNerve cells: long skinny extensionso Intestinal cells: highly folded cell membrane

II. Prokaryotic cells vs Eukaryotic cellsA. Prokaryotic cells

• No nucleus or organelles

• Circular DNA in a nucleoid region

• Cytoplasm and ribosomes surrounded by cell membrane

B. Eukaryotic cells

• Have linear chromosomes in nucleus• Organelles• Bigger than prokaryotic cells

C. All cells have:

• Cell membrane to let things in and out• Ribosomes for protein synthesis• Cytoplasm where many enzymatic reactions

occur• Chromosomes that contain genes

D. Cell wall: protection and support

• in prokaryotic and some eukaryotic cells• cellulose in plants• chitin in fungi• peptidoglycan in bacteria (not archaea)

III. A Tour of Eukaryotic Cells

• Eukaryotic cells have internal membranes forming organelles

• This localizes cellular activities to different parts of cell

• All eukaryotic cells have nearly the same organelles

prokaryote Plant Animal Fungus Protist*

Nucleus

ER

Golgi

MitochondriaChloroplast

lysosome

ribosomes

Cell membraneCell wall

Central vacuolecytoskeleton

A. The endomembrane system is composed of the nucleus, ER, Golgi, lysosomes, vacuoles, and cell membrane1. Evolutionmost widely accepted model is thru invagination of the cell membrane

2. nucleus

What are some structural features of nucleus?

• contains most of the cell’s DNA• surrounded by nuclear envelope that is

double membrane with pores• contains chromosomes and nucleolus

(synthesize ribosomal RNA)• pores regulate what enters and leaves• What enters and leaves?

• RNA that leaves nucleus is used by ribosome to make protein–Free ribosomes are in cytoplasm and

make proteins that stay in cytoplasm–Bound ribosomes are on RER and make

membrane bound proteins or proteins that leave the cell

What tells ribosome to stay free or bind to RER?

3. endoplasmic reticulum (ER): the cell’s factory• highly folded membrane continuous with

nuclear membrane

• types– rough ER (RER)•membrane is studded with ribosomes• it helps synthesize and modify proteins

that will be transported – smooth ER (SER)• no ribosomes on it• it synthesizes carbs and lipids• it detoxifies drugs

• Questions:• a. what type of cell would have a lot of RER?

Why?

• b. what type of cell would have a lot of SER? Why?

4. Golgi apparatus: shipping and receiving

• Flatted stack of membranes found near the RER• It receives proteins from the RER and

packages them for transport out of the cell

5. Lysosomes: digesting center

• membrane bound organelles with digestive enzymes in acidic environment–digest macromolecules (phagocytosis)–digest and recycle old organelles

(autophagy)–digest bacteria and viruses–digest cells destined to be destroyed

(apoptosis)

6. Vacuoles: storage depots• Derived from ER and Golgi• Central vacuole in plants stores water and

gives plant cell its rigid shape

B. Mitochondria and Chloroplasts: convert energy from one form to another

1. mitochondria• double membraned organelle where the

inner membrane is folded into cristae• site of ATP synthesis via aerobic respiration• purpose of cristae?

2. chloroplast• double membraned organelle which contains

stacks of membrane sacs (thylakoids) called grana

• contain chlorophyll• use the energy from the sun to make a

precursor to glucose by photosynthesis• purpose of thylakoids?

List some characteristics of these organelles

3. Evolutionary Origins of Mitochondria and Chloroplasts: Endosymbiont theory

• Have similarities with bacteria–Have ribosomes and DNA similar in size

and structure to bacteria–Same size –Divide independently from rest of cell

http://www.sumanasinc.com/webcontent/animations/content/organelles.html