Cell Theory, Central Dogma and Living Cells

• Cells display immense variation in size, shape, and function

Central Dogma

• The central dogma explains how all cells have similar basic chemistry
• DNA is made from 4 monomers called nucleotides
• Information in DNA is transcribed into RNA
• RNA is translated into protein, a different kind of polymer
• DNA encodes information and directs proteins
• The DNA nucleotide sequence dictates the amino acid sequence in protein
• Proteins catalyze DNA replication and RNA transcription

Living Cells

• Living cells self-replicate with organization, blueprints, and materials
• They use energy and catalytic activity for chemical reactions
• Negative feedback reverses change to maintain normal charge
• Positive feedback amplifies changes
• Example of positive feedback: contractions during birth

Cell Theory

• This states all living cells arise from growth and division of existing cells
• [Scientific] Theory is not a belief, rather an understanding of facts from repeated tests/observation
• All living cells are believed to have evolved from the same ancestral cell (3.5-3.8 bya)
• Genome is the entire DNA nucleotide sequence in an organism
• Mutations during replication can be positive, negative, or silent
• Evolution: process drives modification of species to adapt to the environment
• Different cells in an organism have same genome
• Differentiation is progressive, coordinated change for cells to become specialized
• Cells turn on/off different genes

Microscopy

• There is conventional light microscopy and fluorescence light microscopy
• Conventional light microscopy has magnification up to 1000X with 0.2 μm resolution
• It helps distinguish features of cells
• Fluorescence Light Microscopy can apply liquid staining

Types of Light Microscopy

• Phase contrast provides more detail
• DIC (Differential interference contrast) uses special lenses
• Fixed samples are chemically fixed and sliced to reveal cell components

Fluorescence Microscopy

• Fluorescent dyes help stain cells
• A fluorescence microscope passes illuminating light through two filters
• The first filter selects wavelengths to excite the dye
• The second filter blocks excitation light, passing only emitted light when the dye fluoresces
• Dyed objects appear in bright color on a dark background

Confocal Microscopy

• Confocal microscopy builds an image by scanning a specimen with a laser
• The beam is focused on a single point at a specific depth
• A pinhole aperture allows fluorescence from that point into image
• Scanning generates a sharp image of the focal plane, an optical section
• A series of optical sections at different depths creates a 3D image

Electron Microscopy

• Transmission Electron Microscopy (TEM): stain specimen with heavy metals beam of electrons instead of light
• Using magnetic coils to focus
• TEM has magnification about 1x106 X and resolution down to about 1 nm
• Scanning Electron Microscopy (SEM): stain specimen with heavy metals, beam of electrons is scattered off the surface
• SEM has a good depth of focus and resolution 3 nm - 20 nm and good for surface details

Cell and Component Size

• Use X-ray crystallography to study the position of atoms within the 3-D structure of biomolecules, like proteins
• Resolution down to ~1.5A (0.15 nm)
• X-ray crystallography involves making a crystal with protein

Prokaryotic Cells

• Prokaryotes: simple, yet numerous and enduring (~1030 on Earth)
• Cells contain no nucleus to house genome
• The cell interior appears as a matrix with varying textures
• Prokaryotes lack obvious organized internal structures
• E. coli bacteria has a cell wall, outer membrane, plasma membrane, & cytoplasm

Eukaryotic Cells

• Nucleus stores genetic information in nuclear envelope w/pores allowing stuff in/out
• Mitochondria generate usable energy from food molecules, consuming O2 and producing CO2
• Mitochondria contain their own circular DNA and ribosomes
• They are self-replicating

Organelles

• Endoplasmic Reticulum (ER): interconnected membranous sacs continuous with nuclear envelope
• The ER synthesizes membrane components and materials for other organelles
• Golgi Apparatus: Modifies and distributes molecules via interconnected flattened membranous sacs
• Lysosomes: Vesicles with digestive enzymes such as acids breakdown endocytosed material
• Peroxisomes: Vesicles contain enzymes that utilize O2 and H2O2 to inactivate substances
• The ER materials are sent to other places in cell
• No DNA, but are self-replicating

Specialized Cells

• Endosomes and Secretory Vesicles specialize in Import by endocytosis
• Cytosol: Concentrated Aqueous Gel that functions as watery base environment
• The Cytosol it is crowded w/molecules

Cytoskeleton

• The Cytoskeleton provides Structure, shape, support and is dynamic
• The Cytoskeleton also transports with motor proteins

Cellular Architecture

• Animal cell consists of microtubules, chromatin, ribosomes, flagellum, lysosomes, etc
• Bacterial cell consists of a cell wall, plasma membrane, ribosomes in cytosol
• Plant cell consists of Peroxisome, vacuole, DNA, chloroplast, plasma membrane ,etc

Cell Evolution

• Chloroplasts and Mitochondria Believed to Evolve from Engulfed Bacteria in early anaerobic eukaryotic cell
• The bacteria had symbiotic relationship with eukaryotic cell by shelter and nourishment for power generation.
• Photosynthetic bacteria Live on photosynthesis
• Chloroplasts Capture Energy from Sunlight with chlorophyll pigments
• Chloroplasts produce O2 also Produce Sugers and Self-replicating
• The First Cells may have come from Nonphotosynthetic bacteria

Model Organisms For Study

• Escherichia coli (E. coli) are easy to grow prokaryotes that reproduce rapidly
• Many fundamental processes are similar to our cells such as DNA → RNA → Protein
• Saccharomyces cerevisiae (S. cerevisiae) or Yeasts are easy to gro eukaryotes and reproduce rapidly
• Arabidopsis thaliana or plants : are multicellular with thousands of offspring in 8-10 weeks
• Drosophila melanogaster are suitable for genetic analysis
• Caenorhabditis elegans (C. elegans) was the first multicellular to have genome sequenced
• Zebrafish are vertebrates which are transparent during the first 2 weeks of life and transparent
• Mice are mammals, are and easy to manage
• Human Cells are composed of Fibroblast cells and Neurons in nerve tissue and epithelial cells
• Genomes have a lot of Differentiation and different genes turned on and off