BIOL 215 Lecture 4
The Sedimentation Coeffecient
- Sedimentation coefficient: measures how rapidly a particle sediments under the centrifugal force
- higher sedimentation coefficients mean the particle settles more rapidly
- We use the sedimentation coefficient to see which structures will sediment first
Prokaryotic Subcellular Structures
Cytoplasm
- The cytoplasm consists of the cytosol and subcellular structures
- Cytosol: gel-like semifluid material inside cells that suspends the particles inside the cell
Plasma Membrane
- The plasma membrane is 4-8 nm thick
- It is made of phospholipids and proteins
- The functions of the plasma membrane include:
- serving as a boundary between the cell and external environment
- regulating the movement of particles in and out of a cell
- mediating communication with the external environment
Ribosomes
- Ribosomes are responsible for protein synthesis
- They are a type of ribonucleoprotein complex
- Ribonucleoprotein complex: any particle made out of RNA and proteins
- Sedimentation coefficients for the ribosome and its parts:
- The full ribosome is 70S
- The small subunit is 30S
- The large subunit is 50S
- Some antibiotics can inhibit prokaryotic ribosome activity to kill bacteria
- This doesn’t affect human cells because eukaryotic ribosomes are bigger than prokaryotic ribosomes.
Nucleoid Region
- Nucleoid region: the area in the cytoplasm of prokaryotes where the DNA is located
- This area is not enclosed
Cell Wall
- Peptidoglycan: a polymer made of chains of NAM (N-acetylmuramic acid) and NAG (N-acetylglucosamine) that are cross-linked together by peptide chains
- This is what makes up the cell walls of bacteria
- Some antibiotics interfere with the synthesis of peptidoglycan to kill bacteria
- This doesn’t affect human cells because they do not have peptidoglycan cell walls
- Pseudomurein: a polymer made of chains of NAT (N-acetyltalosaminuronic acid) and NAG (N-acetylglucosamine) that are cross-linked together by peptide chains
- This is what makes up the cell walls of archaea
- Archaean cell walls tend to be more proteinaceous than bacterial cell walls
Eukaryotic Subcellular Structures
Plasma Membrane
- Refer to the section in “Prokaryotic Subcellular Structures” on the plasma membrane
Cytoplasm
- The cytoplasm consists of cytosol, organelles, and other subcellular structures
- Organelles: membrane-bound subcellular structures with specific functions in eukaryotes
Extracellular matrix
- Extracellular matrix: a fibrous network outside of the cell that the cell is tethered to
- Components of the extracellular matrix are generally made of different proteins and/or polysaccharides
- This can vary depending on the cell type
- The extracellular matrix is linked to cells via components on the cell membrane
- Functions of the extracellular matrix:
- Support/structure
- Adhesion to the surrounding medium
Nucleus
- The main function of the nucleus is to store DNA
- Structure of the nucleus:
- 5-6 micrometers in diameter
- Nuclear envelope: a double-layered membrane that surrounds the nucleus
- Nuclear lamina: a network of intermediate filaments beneath the inner layer of the nuclear envelope
- This may also play a role in chromatin organization
- Nuclear pores: regulated openings through the nuclear envelope that control the movement of substances in and out of the nucleus
- Each pore is controlled by a nuclear pore complex
- Nucleolus: clustered regions of genes for rRNA surrounded by specific RNAs and proteins
- this is the site of ribosomal subunit synthesis
Ribosomes
- Still the site of protein synthesis
- The sedimentation coefficients are bigger for each part:
- The full ribosome is 80S
- The small subunit is 40S
- The large subunit is 60S
Rough Endoplasmic Reticulum (RER)
- Rough endoplasmic reticulum: large flattened membrane sheets that temporarily house ribosomes
- The function of the RER is to produce proteins and glycoproteins
- These are then delivered to other parts of the endomembrane system by transport vesicles
Smooth Endoplasmic Reticulum (SER)
- SER looks like RER but without ribosomes
- It is continuous with the RER
- Functions of SER include:
- lipid synthesis
- carbohydrate metabolism
- storing calcium ions
- detoxifying poisons
Golgi Apparatus
- Structure of the Golgi apparatus:
- It is a system of flattened membranous sacs
- Cis Golgi network: the side of the Golgi apparatus closer to the endoplasmic reticulum
- Trans Golgi network: the side of the Golgi apparatus closer to the plasma membrane
Gram Stain
- Gram stain: a technique used to identify bacteria based on characteristics of their cell wall
- Steps of the gram stain:
- Cells are stained with a purple dye
- They are rinsed with alcohol
- Then they are stained with a red or pink counterstain
- Gram-positive bacteria appear to be purple
- This is because the purple dye passes through the peptidoglycan and goes into the cytoplasm
- Gram-positive bacteria have a thick layer of peptidoglycan
- Gram-negative bacteria appear to be pink
- This is because the alcohol rinse washes the purple dye out of the top peptidoglycan layer, allowing the pink dye to enter
- Gram-negative bacteria have an outer membrane and then a thin layer of peptidoglycan around their plasma membrane