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Kaplan MCAT Biology 1

Compound Light Microscope

- requires contrast between cells and cell structures
- contrast is obtained through staining techniques that results in cell death
- use various stains and dyes
ex: hematoxylin (reveals the distribution of DNA and RNA within a cell due to its affinity for negatively charged molecules)

Phase Contrast Microscope

- a type of light microscope
- allows study of living cells
- differences in refractive index are used to produce contrast between cellular structures
-this technique doesn't kill the specimen

Electron Microscope

- uses a beam of electrons to allow a thousandfold higher magnification compared to light microscopy
- can only examine dead specimens
- preparation: fix & section tissues, sometimes stained with solutions of heavy metals

Autoradiography

- uses radioactive molecules to trace and identify cell structures and biochemical activity
- can be used to study protein synthesis
- similar techniques are used to study mechanisms of DNA & RNA synthesis

Autoradiography Preparation

- cells are exposed to a radioactive compound for a brief, measured period of time
- cells are incubated, fixed at various intervals and processed for microscopy
- each preparation is covered with a film of photographic emulsion
- preparations must be kept in the dark for several days while radioactive compound decays
- the emulsion is then developed
- dark silver grains reveal the distribution of radioactivity within the specimen

Centrifugation

- used to separate cells or mixtures of cells without destroying them in process
- lower speed: cell mixtures separate into layers on the basis of cell type
- high speed: fragmented cells' components will sediment at different levels based on their densities
ex: ribosomes (high density) will end up at the bottom of the test tube, mitochondria & lysosomes (low density) remain on top

Prokaryotes

- unicellular organisms with a simple cell structure
ex: bacteria and cyanobacteria (blue-green algae)
- have an outer cell membrane but do not contain any membrane-bound organelles
- have a cell wall, cell membrane, cytoplasm, ribosomes (30S & 50S) & flagella
- have no true nucleus

Nucleoid

- in prokayrotes
- where the genetic material is concentrated as a single molecule of DNA

Plasmids

- in prokayrotes
- smaller rings of DNA, consisting of just a few genes, replicate independently from main chromosome, often contain genes to survive adverse conditions

Eukaryotes

- typically bounded by cell membrane and contains cytoplasm
- Cytosol: fluid component of the cytoplasm and consist free proteins, nutrients & other solutes
- genetic material (linear strands of DNA) organized into chromosomes, located in the nucleus
- Centrioles: found in animal cells but not in plant cells

Cytoskeleton

- found in the cytosol
- composed of microtubules, microfilaments, intermediate fibers
- give cell shape and anchor organelles
- aid intracellular transport

Cell/Plasma Membrane

- encloses the cell and composed of phospholipid bilayer
- outside: hydrophillic (polar) phosphoric acid
- inside: hydrophobic (non-polar) fatty acid
- selective permeability: small non-polar molecules pass through/diffuse freely, charged ions, proteins & carbohydrates don't (need carrier proteins to cross)
- cholesterol molecules: often embedded in hydrophobic interior & contribute to fluidity
- receptors: complex proteins/glycoproteins embedded in - membrane with biding sites, may carry molecule into the cell via pinocytosis

Nucleus

- controls activity of the cell, including division
- surrounded by a nuclear membrane/envelope that maintains distinct environment from cytoplasm
- nuclear membranes have nuclear pores for two way material exchange
- contains DNA
- histones: structural proteins that form chromosomes
- nucleolus: dense structure in the nucleus where ribosomal RNA (rRNA) synthesis occurs

Ribosomes

- sites of protein production
- synthesized by nucleolus
- two subunits: one large and one small
- each subunit is composed of rRNA and proteins
- free ribosomes: found in cytoplasm
- bound ribosomes: line the outer membrane of endoplasmic reticulum

Endoplasmic Reticulum

- a network of membrane-enclosed spaces connected at points with the nuclear membrane
- function: transport materials throughout the cell, mainly secretion
- smooth ER: lipid synthesis
- rough ER: protein synthesis
- these proteins cross to smooth ER, secreted into cytoplasmic vesicles & transported to golgi apparatus

Golgi Apparatus

- stack of membrane-enclosed sacs
- receives vesicles from smooth ER, modifies them, repackages into vesicles & distributes them
- usually active in distributing new materials to cell surface
- exocytosis: when golgi apparatus' secretory vesicles release their contents to the cell's exterior

Vesicles and Vacuoles

- membrane-bound sacs involved in the transport and storage of materials that are ingested, secreted, processed or digested by the cell
- vacuoles are larger than vesicles and are more likely to be found in plant cells

Lysosomes

- membrane-bound vesicles that contain hydrolytic enzymes involved in intracellular digestion
- enzymes are maximally effective at pH 5, thrives in lysosmes
- lysosome is an acidic environment distinct from neutral pH of cytosol
- fuse with endocytotic vacuoles and break down materials ingested by the cell
- aid in renewing cell's own components by breaking down old ones to be recycled in the cytosol
- autolysis: injured/dying cell may commit suicide by rupturing the lysosome membrane & releasing its hydrolytic enzymes, which will digest cellular contents

Microbodies

- membrane-bound organelles specialized as containers for metabolic reactions
- two types: peroxisomes and glyoxysomes

Peroxisomes

- a type of microbodies
- contain oxidative enzymes that produce hydrogen peroxide by the transfer of hydrogen from a substrate to oxygen
- break fats down into smaller molecules that can be used for fuel
- smaller fat molecules also used in the liver to detoxify compounds harmful to the body (ex: alcohol)

Gyloxysomes

- a type of microbodies
- usually found in fat tissue of germinating seedlings
- used by the seedling to convert fats into sugars until the seedling is mature enough to make its own sugar through photosynthesis

Mitochondria

- sites of aerobic respiration within the cell
- suppliers of energy
- each mitochondrion is bound by an outer and inner phospholipid bilayer membrane
- is semiautonomous: contain own (circular) DNA and ribosomes, can produce own proteins and self replicate by binary fission
- believed to have been early prokaryotic cells that evolved a symbiotic relationship with ancestors of eukaryotic cells

Mitochondria's Membrane

- outer membrane: smooth, acts as a sieve, allows molecule through based on size
- intermembrane space: area between the inner and outer membrane
- inner membrane: has cristaes (convolutions) and high protein content that includes the proteins of electron transport chain
- matrix: area bounded by inner membrane, site of many reactions in cell respiration

Cell Wall

- tough outer cell wall
- protects the cell from external stimuli and desiccation
- only on plant cells

Centrioles

- specialized type of microtubule involved in spindle organization during cell division
- not bound by a membrane
- only on animal cells
- oriented at right angles to each other and lie in a region called the centrosome
- direct separation of chromosomes during cell division
- composed of microtubules

Cytoskeleton

- gives cell mechanical support, maintains it's shape and functions in cell motility
- composed of microtubules, mirofilaments and intermediate filaments

Microtubules

- hollow rods made up of polymerized tubulins
- radiate throughout the cell and provide it with support
- provide a framework for organelle movement within the cell
- tubulins make up mirotubules, which make up centrioles

Microfilaments

- solid rods of actin
- involved in cell movement and support
ex: muscle contraction is based on interaction of actin with myosin in muscle cells
- move materials across the plasma membrane in amoeboid movement

Intermediate filaments

- collection of fibers involved in maintenace of cytoskeletal integrity
- diameter falls between microtubules and microfilaments

Movements across the cell membrane

a) simple diffusion
b) facilitated diffusion
c) active transport
d) endocytosis
e) exocytosis

Simple Diffusion

- net movement of dissolved particles down their concentration gradients
- from high concentration to low
- passive process
- types of molecules transported: small/non polar (O₂, CO2, etc)

Osmosis

- simple diffusion of water from a region of lower solute concentration to a region of a higher solute concentration
- if membrane is impermeable to a particular solute, water will flow across membrane until solute concentration differences are equal
- types of molecules transported: H₂O

Hypertonic (in respect to another liquid)

- has a higher solute concentration
- water will flow into the hypertonic liquid

Hypotonic (in respect to another liquid)

- has a lower solute concentration
- water will flow out of hypotonic liquid, into the higher concentrated liquid

Isotonic

- solute concentration between two liquids are equal
- no net flow of water in either direction

Faciliated Diffusion

- passive transport
- net movement of dissolved particles down their concentration gradient
- need help from carrier molecules
- types of molecules transported: large/non-polar (glucose)

Active Transport

- net movement of dissolved particles against their concentration gradient
- need help from transport proteins
- requires energy
- required to maintain membrane potentials in specialized cells (ex: neurons)
- types of molecules transported: polar molecules/ions (Na+, Cl-, K+, etc)

Endocytosis

- process in which the cell membrane invaginates, forming a vesicle that contains extracellular medium

Pinocytosis

ingestion of fluids or small particles

Phagocytosis

engulfing of large particles

Exocytosis

- a vesicle within the cell fuses with the cell membrane and releases its contents to the outside
- in both endocytosis and exocytosis, the material never actually crosses through the cell membrane

Tissues

- groups of morphologically and functionally related cells
- types of tissues: epithelial, connective, nervous and muscle

Epithelial Tissue

- covers the surfaces of the body
- lines the cavities
- protects against injury, invasion and dessication
- involved in absorption, secretion and sensation

Connective Tissue

- involved in body support
- specialized connective tissues: bone, cartilage, tendons, ligaments, adipose tissue and blood

Nervous Tissue

- composed of specialized cells called neurons
- these neurons are involved in the perception, processing and storage of information concerning the internal and external environments

Muscle Tissue

- has great contractile capability
- involved in body movement
- three types: skeletal, cardiac and smooth

Viruses

- acellular structures composed of nucleic acid enclosed by a protein coat
- range in size from 20-300 nm (prokaryotes are 1-10 nm & eukaryotes are 10-100 nm)
- nucleic acid can be either linear or circular and has four varieties: single-stranded & double-stranded DNA, single-stranded and double-stranded RNA

Capsid

- virus' protein coat
- composed of many protein subunits
- may be enclosed by a membranous envelope

"obligate intracellular parasite"

- viruses can only reproduce in a living host cell
- lack structures for independent activity & reproduction
- virus attaches itself to a host cell, injects its nucleic acid, take control of protein synthesis within the cell
- viral genome replicates itself, produce protein coats and assembles new virions that leave host cells
- antiviral meds work by interfering with enzymatic reactions involved in viral replication. it's easier to vaccinate to combat viruses

Bacteriophages

- viruses that exclusively infect bacteria
- injects its nucleic acid into a bacterial cell, the phage capsid doesn't enter the cell

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