Untitled Quiz

Cell Structure and Function

• Cells are the smallest unit of life
• Knowledge of cell structure improves with technological advances
• Cells need to be small or have increased surface area for efficient metabolic activity
• Membranes create compartments within cells
• The endomembrane system is a group of related organelles
• Endosymbiotic theory proposes that mitochondria and chloroplasts evolved from prokaryotic cells
• Prokaryotic and eukaryotic cells differ in their structure and organisation

Cell Theory

• Every organism is composed of one or more cells
• The cell is the smallest unit with life processes
• Continuity of life arises from cell growth and division

Prokaryotic vs Eukaryotic Cells

• Prokaryotic Cells:
  • Lack membrane-bound organelles
  • Contain ribosomes in the cytosol
  • DNA is in a region called the nucleoid
  • Have external structures like cell walls or capsules
  • Eubacteria and archaea are examples
• Eukaryotic Cells:
  • Contain membrane-bound organelles
  • Organelles perform specific functions in the cytosol
  • DNA is in the nucleus
  • Some have cell walls
  • Examples include animal, plant, fungi and protists

All Cells

• Smallest unit of life
• Can survive independently or have the potential to
• Highly organized for metabolic processes
• Sense and respond to their environment
• Have the potential to reproduce

Cell Membranes

• Main component is a lipid bilayer
• Provides cells with fluid properties
• Composed of two layers of phospholipids (hydrophilic heads and hydrophobic tails)

Cell Size

• Most cells are small to maintain a good surface area-to-volume ratio
• Cell volume determines metabolic activity
• Surface area determines the number of substances that can enter or leave the cell

Ribosomes

• Translate nucleotide sequences of messenger RNA into polypeptide chains (protein synthesis)
• Not membrane-bound organelles in eukaryotes
• In eukaryotes, they can be free in the cytoplasm, attached to the endoplasmic reticulum, or inside mitochondria and chloroplasts
• In prokaryotic cells, they float freely in the cytoplasm
• Composed of ribosomal RNA

Microscopes

• Light Microscopes:
  • Create detailed images of small objects
  • Can be simple or compound
  • Wavelength limitations restrict the resolution to roughly 200 nm.
• Electron Microscopes:
  • Use streams of accelerated electrons instead of light
  • Focus electrons using magnets instead of lenses
  • Can resolve structures down to much smaller scales

Eukaryotic Cells Overview

• Contain a nucleus and other organelles

Organelles

• Internal membrane-bound structures for specific functions
• Benefit from compartmentalisation.

Animal Cell Features

• Include specific organelles discussed earlier

Plant Cell Features

• Include specific organelles discussed earlier

Nucleus

• Keeps eukaryotic DNA separate from cytoplasmic activities
• Makes it easier to organise DNA and copy before cell division

Nuclear Envelope

• Double membrane enclosing the nucleus
• Innermost surface has DNA attachment sites

Endomembrane System

• Group of related organelles assembling lipids and modifying polypeptide chains
• Sorting and shipping of products to various destinations

Endoplasmic Reticulum

• Part of the endomembrane system
• Rough ER: Modifies polypeptide chains
• Smooth ER: Manufactures lipids, metabolizes carbohydrates and detoxifies

Golgi Body

• Receives proteins from the RER
• Further modifies, packages, sorts and adds carbohydrates to proteins
• Site of polysaccharide synthesis in plant cells
• Packages finished products for shipment to final destinations

Vesicles

• Membranous sacs that transport materials within cells
• Examples: lysosomes, transport vesicles, peroxisomes

Dynamic Cell Membranes

• Constantly being formed, recycled, and degraded

Mitochondria

• "Powerhouses" of the cell producing ATP
• Double membrane: inner membrane houses the ATP-making machinery

Chloroplasts

• Convert sunlight energy into organic sugars through photosynthesis
• Contain DNA and ribosomes

Mitochondrial/Chloroplast Origin (Endosymbiotic Theory)

• Resemble bacteria
• Have their own DNA and ribosomes
• Divide on their own
• Likely evolved from prokaryotes engulfed but not digested

Specialized Plant Organelles

• Plastids (e.g., chloroplasts, amyloplasts, chromoplasts).
• Central vacuole

Other Plastids

• Chromoplasts: No chlorophyll, abundant carotenoids, pigments in fruits and flowers
• Leucoplasts/Amyloplasts: No pigments, store starch

Apoptosis

• Programmed cell death
• Involves a sequence of events leading to cell destruction
• Cell fragments are engulfed by other cells
• Caused by enzymes called caspases

Autophagy

• Self-eating process where cells recycle their own components

Cytoskeleton

• Present in all eukaryotic cells
• Supports cell shape and internal organisation
• Enables movement of organelles and in some cases, cell motility

Cytoskeletal Elements

• Microtubules, microfilaments, intermediate filaments

Microtubules

• Largest cytoskeletal components
• Composed of tubulin
• Involved in shape, motility and cell division

Microfilaments

• Thinnest cytoskeletal components
• Composed of actin
• Involved in cell movement, shape and maintenance

Intermediate Filaments

• Only in animal cells of certain tissues
• Most stable cytoskeletal elements

Motor Proteins

• Kinesins and dyneins move along microtubules
• Myosins move along microfilaments

Flagella and Cilia

• Structures for cell motility
• 9 + 2 internal structure

Plant Cell Walls

• Secondary cell wall (3 layers): Cellulose and lignin
• Provides support, restricts volume and acts as barrier to infections

Plant Cuticle

• Secretions and waxes accumulate at the plant cell surface
• Semitransparent
• Restricts water loss

Matrices Between Animal Cells

• Hold cells together in tissues
• Contribute to physical properties (e.g., cartilage, skin)
• Filter materials
• Orient cell movement during growth and repair

Plant Cell Junctions (Plasmodesmata)

• Plasma membranes of adjacent cells are continuous
• Water and solutes pass freely between plant cells

Animal Cell Junctions

• Tight Junctions: Anchor cells to form tissues and block materials from passing through the space between cells
• Desmosomes: Anchor cells together in tissues that stretch
• Gap Junctions: Allow communication between cells