Unit 2 – Chapter 1: Cell Structure
Prokaryotic vs Eukaryotic Cells
Feature Prokaryotic Eukaryotic
Nucleus No (DNA is free in cytoplasm) Yes (DNA inside nuclear envelope)
DNA Circular, no histones Linear, associated with histones
Organelles No membrane-bound organelles Membrane-bound organelles present
Cell wall Made of murein (a glycoprotein) In plants – cellulose; in fungi – chitin
Ribosomes Small (70S) Large (80S)
Size Smaller (~0.1–5 µm) Larger (~10–100 µm)
Structure and Function of Organelles (Eukaryotic)
Organelle Structure Function
Double membrane, pores,
Nucleus Contains DNA, controls cell activities
nucleolus
Double membrane, inner Site of aerobic respiration (ATP
Mitochondrion
membrane folded into cristae production)
Double membrane, contains
Chloroplast(plants) Site of photosynthesis
thylakoids and stroma
Modifies, packages, and transports
Golgi apparatus Stack of flattened sacs (cisternae)
proteins and lipids
Transport substances from the Golgi
Golgi vesicles Small membrane-bound sacs
to other parts of the cell
Vesicles containing digestive Break down waste and old cell
Lysosomes
enzymes components
Membrane system covered in
Rough ER Synthesises and transports proteins
ribosomes
Synthesises and transports lipids and
Smooth ER Similar to RER but no ribosomes
carbohydrates
Made of rRNA and protein (80S
Ribosomes Site of protein synthesis
in eukaryotes)
Cell wall (plants) Made of cellulose Provides strength and rigidity
Membrane-bound sac containing Maintains turgor pressure and stores
Cell vacuole
cell sap nutrients/waste
Phospholipid bilayer with Controls movement of substances
Plasma membrane
proteins in/out of the cell
Specialised Cells and Tissues
, Cells differentiate to become specialised for their function.
Groups of similar cells form tissues.
Microscopy
Light Microscope
Uses light; limited resolution (~200 nm)
Magnification up to ~1500×
Can view living cells
Electron Microscope
Uses electrons; higher resolution (~0.1 nm)
Higher magnification (~500,000× or more)
Can only view dead cells (vacuum required)
Type Key Feature
TEM (Transmission) Highest resolution, shows internal ultrastructure
SEM (Scanning) 3D surface images, lower resolution than TEM
Calculations
Magnification formula:
Magnification=Image sizeActual sizeMagnification=Actual sizeImage size
Convert units carefully:
1 mm = 1000 µm = 1,000,000 nm
Cell Fractionation and Ultracentrifugation
Used to isolate organelles from cells.
Steps:
1. Homogenisation – break cells open in ice-cold, isotonic, buffered solution
2. Filtration – remove cell debris
3. Ultracentrifugation – spin at increasing speeds to separate organelles by mass
Order of sedimentation (heaviest first):
Nuclei → chloroplasts → mitochondria → lysosomes → ribosomes
Prokaryotic vs Eukaryotic Cells
Feature Prokaryotic Eukaryotic
Nucleus No (DNA is free in cytoplasm) Yes (DNA inside nuclear envelope)
DNA Circular, no histones Linear, associated with histones
Organelles No membrane-bound organelles Membrane-bound organelles present
Cell wall Made of murein (a glycoprotein) In plants – cellulose; in fungi – chitin
Ribosomes Small (70S) Large (80S)
Size Smaller (~0.1–5 µm) Larger (~10–100 µm)
Structure and Function of Organelles (Eukaryotic)
Organelle Structure Function
Double membrane, pores,
Nucleus Contains DNA, controls cell activities
nucleolus
Double membrane, inner Site of aerobic respiration (ATP
Mitochondrion
membrane folded into cristae production)
Double membrane, contains
Chloroplast(plants) Site of photosynthesis
thylakoids and stroma
Modifies, packages, and transports
Golgi apparatus Stack of flattened sacs (cisternae)
proteins and lipids
Transport substances from the Golgi
Golgi vesicles Small membrane-bound sacs
to other parts of the cell
Vesicles containing digestive Break down waste and old cell
Lysosomes
enzymes components
Membrane system covered in
Rough ER Synthesises and transports proteins
ribosomes
Synthesises and transports lipids and
Smooth ER Similar to RER but no ribosomes
carbohydrates
Made of rRNA and protein (80S
Ribosomes Site of protein synthesis
in eukaryotes)
Cell wall (plants) Made of cellulose Provides strength and rigidity
Membrane-bound sac containing Maintains turgor pressure and stores
Cell vacuole
cell sap nutrients/waste
Phospholipid bilayer with Controls movement of substances
Plasma membrane
proteins in/out of the cell
Specialised Cells and Tissues
, Cells differentiate to become specialised for their function.
Groups of similar cells form tissues.
Microscopy
Light Microscope
Uses light; limited resolution (~200 nm)
Magnification up to ~1500×
Can view living cells
Electron Microscope
Uses electrons; higher resolution (~0.1 nm)
Higher magnification (~500,000× or more)
Can only view dead cells (vacuum required)
Type Key Feature
TEM (Transmission) Highest resolution, shows internal ultrastructure
SEM (Scanning) 3D surface images, lower resolution than TEM
Calculations
Magnification formula:
Magnification=Image sizeActual sizeMagnification=Actual sizeImage size
Convert units carefully:
1 mm = 1000 µm = 1,000,000 nm
Cell Fractionation and Ultracentrifugation
Used to isolate organelles from cells.
Steps:
1. Homogenisation – break cells open in ice-cold, isotonic, buffered solution
2. Filtration – remove cell debris
3. Ultracentrifugation – spin at increasing speeds to separate organelles by mass
Order of sedimentation (heaviest first):
Nuclei → chloroplasts → mitochondria → lysosomes → ribosomes
