BIO 011 Lecture Notes - Lecture 4: Lipid Bilayer, Cell Membrane, Endomembrane System
Chapter 5 – Cells
Jadzia Wray
Cell theory of biology
- Cells are the fundamental units of life
- All organisms are composed of cells
- All cells come from preexisting cells
Internal structure of cells
- Nucleus: holds DNA (genetic material) (nucleus is encased in a membrane)
- Endomembrane system: ER, golgi complex, etc.
- Cytoskeleton: actin, microtubules, and tubulin
Cell Membranes
- The plasma membrane is the outer surface of every cell and has more or less the same structure
in all cells. Encases the cell.
- It is made of a phospholipid bilayer with embedded proteins and other molecules
o Membranes or fluid platforms where chemistry occurs
o Also are barriers and keep bad things out and good things in
Function of the membrane
- Selective permeable barrier
o Hydrophobic inside and hydrophilic outside so that polar molecules can go through
o Channel proteins are gated to allow for passage of certain molecules
- Allows cells to maintain a constant internal environment (homeostasis)
- Is important in communication and receiving signals
o Serves as a platform for chemical reactions
o Receptor proteins that are lodged in proteins. Are important for cells to move around
or stay in place
- Often has proteins for binding and adhering to adjacent cells
What are the main structural differences between prokaryotic and eukaryotic cells?
- DNA organization
o Prokaryotes: no nucleus or other membrane-enclosed compartment for DNA
o Eukaryotes: membrane-enclosed nucleus contains DNA
- Eukaryotic cells are typically much larger than prokaryotic cells
- Prokaryotes: cytoplasm has ribosomes, DNA in nucleoid, cell wall made of peptidoglycan, some
contain chlorophyll for photosynthesis, some have flagella and some have pili
Chloroplasts and Mitochondria evolved from bacteria and evolved to form a different relationship with
the cell where they make energy
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The Prokaryotic cell
- Organized DNA is called the nucleoid not
the nucleus. It is a dense blob of DNA
- Incredible variety
- Use many different sources of energy
and live in many different environments
- Phospholipid bilayer that encases the
cytoplasm
- The membrane is a symmetrical
phospholipid bilayer: polar hydrophilic head
groups and nonpolar hydrophobic tails
- The cell wall is a polymer of sugars called the peptidoglycan
- The outer membrane is asymmetrical and has phospholipids inside and has a weird sugar piece
on its outer part. Inner membrane is symmetrical phospholipid bilayer and outer membrane is
asymmetrical.
- Some of the most awful drug-resistant bacteria have the two membranes
- Capsule (made of sugar and on the outside) – good at warding off immune system
- ORDER FROM IN TO OUT:
o Cytoplasm
o Inner membrane
o Cell wall (peptidoglycan – polymer of sugars)
o Maybe an outer membrane (depends on bacteria) (asymmetrical bilayer)
o Maybe have a capsule (big pile of polysaccharide) (depends on bacteria)
Bacteria have many shapes
- Cocci (sphere – round cell) and bacilli
- Can be organized as chains, or
structures
- Staff infection → staphylococci – round
cell
- Strep throat → streptococci – round
cell chain
- The others have different cytoskeleton
elements giving them their different
shapes
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Prokaryotic Flagella
- Bacterium has outer and inner membrane
- Flagella are huge they can be 10 to 20 times the
length of the bacteria
- Why does the bacteria have so many flagella?
o With many flagella, the bacteria will be able to
resist any flow to flush them out and they can
swim up
o How to avoid a urinary tract infection?
▪ Just pee. But flagella helps bacteria
that causes the UTI to avoid being
peed out.
Bacterial Pili
- The pili is a tube used to transfer DNA between the
bacteria
The Eukaryotic Cell
- The nucleus is usually the largest organelle
o Contains DNA
o Site of DNA replication
o Site where gene transcription is turned on or off
o Assembly of ribosomes begins in a region called the nucleolus
▪ Ribosomes are in the rough ER
- DNA Organization
o In the nucleus, DNA combines with proteins to form chromatin in long, thin threads
called chromosomes.
o Before cell division, chromatin condenses, and individual chromosomes are visible in the
light microscope
o One strand for prokaryote, many for eukaryote
o In eukaryote → chromosomes are linear
o In prokaryote → chromosomes are circular
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Cells are the fundamental units of life. Nucleus: holds dna (genetic material) (nucleus is encased in a membrane) The plasma membrane is the outer surface of every cell and has more or less the same structure in all cells. It is made of a phospholipid bilayer with embedded proteins and other molecules: membranes or fluid platforms where chemistry occurs, also are barriers and keep bad things out and good things in. Selective permeable barrier: hydrophobic inside and hydrophilic outside so that polar molecules can go through, channel proteins are gated to allow for passage of certain molecules. Allows cells to maintain a constant internal environment (homeostasis) Is important in communication and receiving signals: serves as a platform for chemical reactions, receptor proteins that are lodged in proteins. Are important for cells to move around or stay in place. Often has proteins for binding and adhering to adjacent cells.
