Chapter 6: A Tour of the Cell

Light microscopes

Visible light passes through the specimen and through a glass lens, light is refracted to magnify specimen, can observe living things

Magnification, resolution, and contrast

M: ratio of an object’s image size to real size; R: clarity of the image (minimum distance 2 points can be separated and still distinguishable); C: Accentuates differences in parts of the sample

Magnification and resolution relationship

When magnification increases, resolution decreases, and vice versa

Organelles

Membrane-enclosed structures in eukaryotic cells

Electron microscopes

Focus beams of electrons through specimen; specimen cannot still be living, must be coated in metal ions

Scanning Electron Microscope

Scans the surface of a sample, the bean excites electrons and secondary electrons are detected, 3D image results

Transmission Electron Microscope

Internal cell structure, beam goes through a thin section of the specimen

Cytology

The study of cell structure

Cell fractionation

Takes cells apart and separates major subcellular structures to determine their individual functions; 1. homogenization (blender), 2. Centrifuge at different speeds and lengths of time for different things

Prokaryotic domains and eukaryotic domains

Bacteria and archaea, eukarya

Things all cells have

Plasma membrane, cytosol, chromosomes, ribosomes

ECs vs. PCs

ECs have nucleus bound by a double membrane, PCs have nucleoid instead that is not membrane-enclosed, no organelles

Cytoplasm vs. cytosol

Cytoplasm is all contents within membrane (excluding nucleus), cytosol is just the fluid

Surface area and volume of a cell

As cells increase in size, their volume increases more than their surface area (one of the reasons cells are smaller, because they need enough surface area to accommodate volume)

Microvilli

long, thin projections that increase surface area without impacting volume much

In animal cells but not plant cells:

Lysosomes, centrosomes, flagella (although maybe some plant sperm)

In plant cells but not animal cells:

Central vacuole, chloroplasts, cell wall, plasmodesmata

Nucleus

Contains most of the cell’s genes, enclosed by double membrane (nuclear envelope) that has pores

Nuclear lamina

Net-like array of protein filaments, maintains shape of nucleus

Chromosomes, chromatin

Store genetic information, the complex of DNA and proteins that coil to form chromosomes

Necleolus

Synthesizes rRNA, proteins from cytoplasm assembled with rRNA

Ribosomes

rRNA and protein, responsible for protein synthesis

Endomembrane system

Inside the membrane; nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuole,s plasma membrane

Vesicles

sacs made of membrane that transport things

Endoplasmic reticulum

Network of membranes, often makes up more than ½ total cell membrane, separates internal compartments from cytosol

Smooth ER

Detoxifies drugs/poisons, metabolic processes, stores calcium, synthesis of certain macromolecules

Rough ER

Protein production (as polypeptide chain grows, the chain threads into the RER lumen), membrane factory for the cell

Glycoproteins

carbs covalently bonded to proteins

Golgi apparatus

Warehouse of the endomembrane system, transport vesicles go here after leaving ER, cisternae, sort, ship, and manufacture

Cis face of GA

Receives materials, near the ER

Trans face of GA

Ships materials

Lysosomes

Membranous sac of hydrolitic enzymes that animals use to hydrolyze macromolecules, work best in acidic environment

Phagocytosis

protists eat by englufing smaller organisms or food particles, when done within a cell (i.e. food vacuole with lysosome) the digestion products become food for the cell

Autophagy

Recycle cell’s material

Vacuoles

large vesicles from ER and GA, food, contractile (pump excess water out of cell to maintain proper concentration of ions and molecules), central (plant cells, plants enlarge as this fills with water)

Mitochondria

Sites of cellular respiration (Oxygen to ATP), inner membranes are convoluted, intermembrane space and mitochondrial matrix

Chloroplasts

Sites of photosynthesis, chlorophyll, thylakoids and granum, stroma

Mitochondria and chloroplast similarties

Endosymbionts, have DNA of their own, have ribosomes, autonomous, double membrane

Plastids

A family of plant organelles (i.e. amyloplast which stores amylose, or starch, and chromoplast which gives fruits and flowers their orange and yellow hues)

Peroxisomes

Produce hydrogen peroxide and convert to water, detoxify alcohol in liver by taking H from poisons, break down fatty acids

Glyoxysomes

Help convert fatty acids to sugar, in plant seeds (energy and carbon source before plants can photosynthesize)

Cytoskeleton

Microtubules, microfilaments, intermediate filaments, organizes structure, can be dismantled and rebuilt, changing cell shape, motor protein feet used by organelles to walk along cytoskeleton

Microtubules

hollow tubes for cell shape, motility, chromosome and organelle movement, tubulin protein connected by a dimer (molecule with alpha and beta subunits)

Centrosomes, centrioles

Microtubule-organizing center, within centrosome (9 sets of triplet microtubules in a ring)

Basal body, dyneins

Form the base of cilium, pairs of protruding proteins spaced along the length of an outer doublet reaching toward neighboring doublet

Microfilaments

soild rods, built from actin, bear tension, make cortex (outer cytoplasmic layer) more gel than liquid

Myosin

like dynein in microtubules

Intermediate filaments

more permanent, often persist after cells die (i.e. keratin proteins in dead skin cells on outer layer of our skin)

Cell wall composition

Generally microfibrils made of cellulose (produced by cellulose synthase) embedded in matrix of other polysaccharides and proteins

Primary cell wall

Young plant cell’s first wall, thin and flexible

Middle lamella

Glues primary and adjacent walls together, pectins (thin and sticky polysaccharides used as thickening agents in jams and jellies)

Secondary cell wall

Between plasma membrane and primary cell wall, sometimes made to strengthen its wall (other times they just harden the primary wall)

Extracellular Matrix (ECM)

Provides structural support and cell signaling, consists of glycoproteins such as collagen and fibronectin, as well as other carb-containing molecules

Plasmodesmata

Cytoplasmic channels through cell walls

Tight junctions

tightly pressed plasma membranes, prevent leakage of fluid

Desmosomes

AKA anchoring junctions, fasten cells together into sheets, attach muscle cells

Gap junctions

Most like plasmodesmatas of plant cells, but not lined with membrane, allows passage of amino acids, sugars, ions, and other small molecules