bio ch 6
Overview of Cells
The cell is the basic unit of structure and function in organisms.
Internal Organization of Eukaryotic Cells
Internal organization allows eukaryotic cells to perform essential life functions.
Microscopes and biochemistry are crucial for studying cells due to their small size.
Microscopy Techniques
Types of Microscopes:
Light Microscope (LM): Uses visible light and glass lenses to magnify images.
Electron Microscopes (EMs): Two types:
Scanning Electron Microscopes (SEMs): Provides 3-D images of specimen surfaces.
Transmission Electron Microscopes (TEMs): Examines internal structures by transmitting electrons through the specimen.
Key Parameters of Microscopy:
Magnification: Ratio of image size to real size.
Resolution: Clarity of the image and minimum distance between distinguishable points.
Contrast: Visibility differences in brightness between sample parts.
Recent advances include techniques that enhance detail and allow for live cell visualization.
Cell Fractionation
Technique to separate organelles from cells using centrifugation.
Helps determine organelle functions.
Eukaryotic cells compartmentalize functions using internal membranes.
Cells can be categorized into two types: prokaryotic and eukaryotic.
Comparing Prokaryotic and Eukaryotic Cells
Basic Features of All Cells:
Plasma membrane, cytosol, chromosomes, ribosomes.
Prokaryotic Cells:
No nucleus, DNA in nucleoid region, no membrane-bound organelles.
Eukaryotic Cells:
DNA within a nucleus, membrane-bound organelles, generally larger sizes.
Surface area to volume ratio critical for cell function, affecting metabolic efficiency.
Structure of Eukaryotic Cells
Cell Compartments:
Internal membranes organize functions within the cell, allowing for incompatible processes.
The structural unit is primarily composed of a phospholipid bilayer.
Nucleus and Ribosomes
The nucleus contains most cell DNA, regulating protein synthesis via ribosomes.
Nuclear Envelope: Double membrane structure with pores regulating molecule entry/exit.
Chromatin: DNA packaging material that condenses into chromosomes during cell division.
Endomembrane System
Components include:
Nuclear envelope, ER, Golgi apparatus, lysosomes, vacuoles, plasma membrane.
Functions include protein traffic regulation and metabolic processes.
Endoplasmic Reticulum (ER):
Smooth ER: Synthesizes lipids, detoxifies, stores calcium ions.
Rough ER: Has ribosomes, processes proteins for secretion.
Lysosomes and Vacuoles
Lysosomes contain hydrolytic enzymes for digestion and recycling organelles (autophagy).
Vacuoles serve various functions:
Food vacuoles formed by phagocytosis.
Central vacuoles in plant cells store sap and regulate growth.
Energy Conversion Organelles
Mitochondria: Sites of cellular respiration, producing ATP with double membranes.
Contain their own DNA and ribosomes, supporting the endosymbiont theory.
Chloroplasts: In plants, conduct photosynthesis; contain thylakoids and stroma.
Peroxisomes
Metabolic compartments that detoxify substances and break down fatty acids.
Cytoskeleton Functions
Fibrous network providing support and maintaining cell shape. Built from:
Microtubules: Thicker fibers guiding organelle movement, involved in chromosome separation.
Microfilaments: Thinnest, support cell shape, and contribute to motility and cytoplasmic streaming.
Intermediate Filaments: More permanent components that anchor organelles.
Extracellular Components
Plant Cell Walls: Provide protection, shape, and prevent excessive water uptake.
Extracellular Matrix (ECM) in Animals: Composed of glycoproteins, regulates cellular behavior via integrin interactions.
Cell Junctions
Prevent leakage (tight junctions), anchor tissues (desmosomes), and allow communication (gap junctions).
Integration of Cell Components
Cell functions require coordinated activities of all parts, illustrated by macrophage bacteria destruction.