CELL STRUCTURE CH 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 n 2 while volume increases by n 3 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 volume o Organelles o Plant cells : large central vacuole o Nerve cells: long skinny extensions o Intestinal cells: highly folded cell membrane

II. Prokaryotic cells vs Eukaryotic cells A. 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

prokaryotePlantAnimalFungusProtist* Nucleus ER Golgi Mitochondri a Chloroplast lysosome ribosomes Cell membrane Cell wall Central vacuole cytoskeleton

A. The endomembrane system is composed of the nucleus, ER, Golgi, lysosomes, vacuoles, and cell membrane 1. Evolution most 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 t/organelles.html