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

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