Biology Notes (Exam Guide 5)

The cell

• basic unit of structure and function essential to life

• perform all essential life processes

• can be specialized for a particular

• a shared evolutionary history

prokaryotic cells

• tiny

• nucleoid (DNA unbound)

• ribosomes in the cytosol

• no organelles

• plasma/cell membrane

• cell wall

• divide by binary fission

eukaryotic cells

• larger

• DNA inside nucleus

• membrane bound organelles

• ribosomes in cytosol

• some have a cell wall

• divide by mitosis

Common features of all cells

• bound by plasma membrane

• distinct internal environment

• genetic info 

• reproduce by division 

• carry out metabolism 

• homeostasis 

• small size 

Limits to cell size

1.plasma membrane

- all material must pass to enter cell

- surface area limits rate

2. advantageous to maximize surface area to volume ratio

archaean cells are prokaryotic

Nucleus

• structure is surrounding membrane = nuclear envelope

• inside the DNA is organized was linear chromosomes

- DNA + proteins = chromatin

- nucleolus makes ribosomes

- RNA and proteins, no membrane

Nucleolus

makes ribosomes

nuclear envelope 

• 2 membranes, both lipid bilayers 

• inside lined by nuclear laminate 

- proteins

- maintains nucleus shape

• transport regulated by nuclear pores

Mitochondria

• membranes

• have own DNA

• have own ribosomes

• undergo binary fission 

• aerobic asporation 

chromoplasts

• photosynthesis

• only found in photosynthetic lineages, mostly plants and algea

endosymbiosis theory

• double membrane

• similar size, enzymes, and ribosomes to bacteria

• DNA sequences very similar to living bacteria

• Some parts of the cell were once free-living bacteria that got swallowed by a large cell a long time ago, instead of being digested, they started living inside the larger cell and helped each other - a partnership that apparently became permanent

Ribosomes

• all cells have ribosomes

• its structure is non membrane bound, not organelles 

• ribosomal RNA (rRNA) and proteins

• its function is to synthesis primary polypeptides 

• types of ribosomes:

- free: all cells (and mitochondria and chloroplasts)

- bound: attached to rough endoplasmic reticulum (ER)

Endomembrane system

• phospholipid bilayers inside (endo) cell

• no free ends: closed compartments

• separates: internal and external

• lumen inside space

• its strucuture is a phospholipid bilayer either:

- continuous: one long structure

- connected via vesicles: transfer membrane segnments

• its function regulates protein folding/movement metabolic functions

plasma membrane

• surround all cells- encloses cell contents

- cell wall selectively permeable

• regulates what and how much passes through membrane

nuclear envelope

• encloses DNA

• instructions for a protein (mRNA) leave through nuclear pores leads to ribosomes and primary polypeptide

Endoplasmic Reticulum (ER)

• ER continuous with nuclear envelope

• two regions, smooth with no ribosomes and rough with ribosomes

Rough ER Functions

1. proteins folded and modified

2. secrete glycoproteins (proteins bonded carbs)

3. distributes transport vesicles

4. cell membrane factory

Smooth ER functions

1. synthesis lipids

2. metabolizes polysaccharides (breaks down glycogen)

3. detoxifies drugs and poisons 

4. stores calcium ions Ca2+

Golgi apparatus

• its structure is stacks of membrane sacs = cicsternae

• not continuous with ER

- cis face: “recieving” side from ER

- trans face: “shipping” side

• its functions are:

1. modifies ER products

2. sorts and package

3. manufactures some macromolecules

4. shipping product using transport vesicles

lysomes

• sacs of hydrolytic enzymes “cell stomach’

• primary lysosomes, buds off Golgi - no food yet

- food enters in vacuole which then fuses with lysosome which forms

• secondary lysosomes break down complex molecules

vacuoles

• maintenance compartments 

• its membrane-bound containers from ER and Golgi apparatus

• its functions vary by cell:

1. food vacuoles stores food

2. contractile vacuoles, pump water out

3. central vacuoles, (plant cells) hold water