Bio-Bases MID-TERM EXAM Study Guide
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See: Quiz #1 study guide
Biochemistry
Bio-Molecular Quartet: four primary types of biologically important molecules
1) Carbohydrates:
(a) sugars: saccharides and polysaccharides
(b) Often 6-carbon rings
(c) Short-term energy supply & molecular recognition (to identify if a cell belongs)
2) Fatty Acids:
(a) fats: polymers are called lipids
(b) lumpy head with multiple straight carbon chains
(c) Long-term energy storage
(d) head is hydrophilic, tail is hydrophobic (cf. bi-lipid cell membrane)
3) Amino Acids:
(a) building block of proteins and enzymes
(b) There are 20 different types; 8 – 9 are essential:
(i)
tryptophan (precursor to seratonin & melatonin), etc.
(ii)
Histidine (cannot be make by children; adults can make)
(c) AA, peptides (small group of Aas), polypeptides, proteins
(d) Coded by nucleic acid tiplets in DNA/RNA – 64 combinations for 20 amino acids
4) Nucleic Acids:
(a) Forms the basis of the genetic code.
(b) DNA: Adenosine, Cytosine, Guanine, Thymine (ACGT)
(c) RNA: Adenosine, Cystosine, Guanine, Uracil
DNA
1) two interwoven strings of nucleic acids form the “double helix”
2) strands are complementary
(a) Adenoscine matches with Thymine (A – T)
(b) Cytosine matches with Guanine (C – G)
3) Compression of DNA
(a) helix wound onto spools: histones
(b) strings of histones from chromatin fibers
(c) fibers loop and coil into chromatids
(d) two chormatids joined by centromere to form a chromosome
4) Structure of DNA
(a) each chromatid carries several to several thousand genes (20-30 K in humans)
Genetics
1) Humans normally have 23 pairs of chromosomes (46 total)
(a) Extra 21st chromosome = Down Syndrome
2) Monogenetic Traits:
(a) single gene controls the presence or absence of trait
3) Polygenetic Traits:
(a) several to many genes invovled
(b) most human bxial and personality traits and mental health problems
4) Sex-linked traits:
(a) resided on X chromosome; males more likely to get them
5) Sex-limited traits:
(a) present in both sexes but have an effect in one sex only; or much stronger effect in one sex than other.
Heritability
1) def: an estimate as to how much of the variance in some characteristic within some population is due to
heredity
2) genetic does not necessarily imply heritable!
3) compare resemblence b/w monozygotic (identical) and dizygotic (fraternal) twins; if monozygotic twins are
more similar, suggests heritability
4) Some common findings:
III)
A)
B)
C)
D)
E)
F)
G)
H)
I)
J)
K)
L)
IV)
A)
(a) personality traits: .5
(b) Schizophrenia, depression: .5 -.6
(c) IQ - .7
(d) Bipolar - .8
(e) Huntington’s – 1.0
Cell Biology
About 50 trillion cells in the human body
Cell Membrane
1) Bi-lipid: two layers of lipids, tail to tail form membran
2) fluid: always in motion, but has some structural strength thanks to micro-tubules
3) maintains intracellular environment
Nucleus
1) stores genetic material
2) surrounded by porous nuclear envelope
3) Important genes are copied via RNA, exported through nuclear pores to the ER for synthesis
Ribosomes
1) synthesize proteins from AA
2) found in Rough ER
3) take orders from the RNA and put amino acids together in the order specified by RNA
Endoplasmic Reticulum
1) Rough ER:
(a) contiguous with nuclear membrane
(b) embedded with ribosomes
(c) responsible for protein synthesis
2) Smooth ER:
(a) no ribosomes
(b) generates steroid and lipid synthesis (not proteins)
Golgi Apparatus
1) packages proteins produced by ER into packets called vesicles
Mitochondria
1) energy production – glucose to ATP
2) some cells only have a few – NERVES AND MUSCLES have hundreds or more
3) have their own small DNA – inherited from Mother
Microtubules / Microfilaments
1) Provide cellular structure (i.e., scaffolding)
2) Protein / organelle transport
Centrioles
1) specialized groups of microtubules
2) helps divide cell during osmosis (moves DNA pairs to opposite ends of cell)
3) NOT PRESENT IN NERVES
Microvilli
1) hair-like projectsions that increase surface area (not tubule-based)
2) used for absorption in intestines, nose, lungs
Cell Reproduction
1) At conception – one cell; 23 chormosomes from egg, 23 from cell
2) All cells of 1st several generations are identical
3) SPECIALIZATION occurs at 5th or 6th generation
Types of Junctions:
1) Tight junctions: impenetrable junctions (e.g., in the blood-brain barrier) cells are joined tightly by proteins, so
that extracellular fluids cannot flow between them.
2) Gap junctions: loose junctions that allow substances to pass; often have intercellular tubes connecting cells.
3) Adhesion Junction: have structural connection protein
Nerve Cells
Specializations:
1) No centrioles (CANNOT REPLICATE)
2) Long life (must last a life time)
3) Are long and narrow instead of “roundish” like most other cells
4) Have Nissl Bodies:
(a) Specialized rough ER
(b) Handle neurotransmitter synthesis
5) Extremely high metabolic rate
(a) Many more mitochondria than other cells (tend to have several thousands)
6) Create action potentials, electrical pulses
B)
Gross Organization:
1) Dendrites: Receptive branches of the cell – tend to have very many
2) Axon: the sending end of the cell – usually one
(a) Arises from axon hillock
(b) Impulse generation and transmission
(c) Ends in a terminal button
C)
Classifications:
1) Multipolar: several processes (many dendrites + axon)
2) Bipolar: 2 processes (rare, mostly in sensory)
3) Unipolar: (pseudo) – one process; from as bipolar and then the proximal processes merge into one; mostly
found in PNS
D)
HELPERS (aka glial cells)
1) Help during migration (during development)
2) The Mylenators:
(a) PNS: Schwann cells
(b) CNS: oligodendrocytes
3) Astrocytes: (in CNS)
(a) Hold nerves in place, anchor to blood supplies; maintain extraneuronal environments
4) Microglia:
(a) Monitor nerve health; phagocytosis(?)
Action Potentials and Synapses
V)
Action Potentials
Spikes of electrical activity exhibited by nerves
Almost always less than 1000 per second
Almost all neurons create APs (some retinal cells only have graded potentials)
Remember!!
1) Opposite Charges Attract (like charges repell)
2) Concentrations equalize
E)
The Nerve Cell at Rest
1) Normal nerve potential is approx – 70 mv with respect to extracellular space
2) Concentrations of Ions
(a) Inside Cell:
(i)
Lots of K+ (potassium)
 Wants to move out of cell b/c of concentration gradient
(b) Outside Cell:
(i)
WHOLE LOTS of Na+ (sodium)
 Wants to move into cell b/c of concentration gradient AND charge
(ii)
A little Cl- (chlorine)
 Wants to move into cell b/c of concentration gradient
3) The Sodium-Potassium Pump
(a) Pumps Na+ out of cell and K+ into cell
(b) Takes energy (ATP)
(c) Maintains the negative potential of the nerve cell at rest
4) Ion Channels
(a) 4-7 transmembrane proteins (the same protein chain loops back and forth through the membrane 4 – 7
times)
(b) Typically only pass one kind of ion (relatively selective – due to either size of opening vs. ion)
A)
B)
C)
D)
(c) Activated by ligands (key molecules), voltage, or time (also pressure in some cases)
(d) Types of channels:
(i)
Passive: ionic movement by gradient
(ii)
Facilitated transport: helper proteins assist
the movement of a molecule across the
membrane (occurs spontaneously)
(iii)
Active transport: ENERGY required; 2
ions transported at once (aka symport)
F)
G)
H)
VI)
A)
B)
C)
The Process of the Action Potential
1) The cell is resting at –70 mv (all channels are closed)
2) “something” opens keyed Na+ channels
(a) something = neurotransmitters
3) Na+ enters the cell, depolarizing the cell = gradual
rising toward 0 of electric potential
4) When potential = -40 mv (aka, the threshold), many
more volatage controlled Na+ channels open, causing massive influx of Na+ ions = rapid rising of electric
potential of cell toward and above 0 mv (to +30 mv).
5) Na+ channels close and voltage controlled K+ channels open (at +30mv). K+ flows out of cell, repolarizing it
(the falling phase of the potential).
6) The Na+/K+ pump restores equilibrium.
Propogation and Results at Synapse
1) Action potential is propogated down the axon as a result of local depolarization triggering peripheral
polarization, etc….. and down the line (like a fuse)
2) Terminal Buttons
(a) Depolarization at the terminals results in opening Ca++ channels – letting Ca++ into terminal
(b) This triggers fusion of neurotransmitter vesicles to the membrane
(i)
Completed by SNARES: which keep vesicles proximal to membrane, and comlete fusion of
membran to vesicle during Ca++ influx.
(c) Neurotransmitter is released.
3) Neurotransmitter Synthesis
(a) AAs and amine neurotransmitters are synthesized IN TERMINAL BUTTON
(b) All others (including peptides, larger proteins) are manufactured in cell body and transported via
transporter proteins “walking” down microtubules in the axon at rate of up to 1 m per day.
Important Action Potential Information
1) Refractory Periods: periods of time after a potential where another potential cannot be generated
(a) Absolute: about 1 mSec; cannot fire again; due to time-activated gate in the Na+ voltage-controlled
channels.
(b) Relative: about 5-10 mSec; can fire again with more stimulation; due to undershoot; need to bring in more
positive charges due to hyperpolarization
2) Rate:
(a) limited to about 1000 per sec – due to absolute refractory period
(b) varies with stimulution, but almost never ceases entirely
Synapse
Def: The space between the terminal button of the presynaptic nerve and the dendrite, etc., of the postsynaptic
cell.
Synaptic Transmission:
1) neurotrasmitter diffuses across the synapse and binds to receptors on the postsynaptic nerve
2) When enough stimulation has been received, the postsynaptic nerve fires an AP
3) Presynaptic autoreceptors limit neurotransmitter release
(a) they receive the neurotransmitter as well, to signal to pre-syn cell how much has been released
4) Excess neurotransmitter is destroyed or reuptaken into the pre-syn nerve
Different Keys
1) Neurotransmitters:
(a) from presyn cell; very localized action
(b) neuron to neuron – fast acting and direct
D)
E)
F)
VII)
A)
B)
2) Neuromodulators:
(a) from nearby cells; local area, longer term reaction
3) Hormones:
(a) transported via blood, not neurons
(b) systemic; long-term action
Inhibition
1) Inhibitory channels allow Cl- to flow into cell, hyperpolarizing it
2) Decreases the likelihood of an AP b/c cell is more negative than usual, needing more Na+ than usual to reach
threshold.
3) Usual neurotransmitters:
(a) GABA, Seratonin, etc.
Many thousands of inputs usually necessary to reach threshold
Postsynaptic Effects
1) Direct effect on ion channels
(a) neurotransmitter (nt) binds to receptor channel, opening it
(b) quickest acting and shortest effect
(c) nt remains in synapse until destroyed or reuptaken
2) Secondary Messenger Systems
(a) guanine-sensitive protein (G-protein) is linked to the receptor
(b) G-protein activates enzyme
(c) enzyme produces “second messenger” (e.g., cAMP)
(d) 2nd messenger can effect other receptors or influence protein synthesis
(i)
effect other receptors by “keying” them from the inside of the cell
(e) Common Types
(i)
cAMP, IP, Diacylglyceride
(f) Purposes:
(i)
slower effect
(ii)
longer lasting
(iii)
AMPLIFICATION – detection of small stimulation and amplify
3) Direct Gene Activation
(a) primarily by lipid-soluble steroids
(b) pass through membrane, led to cell by chaperonin
(c) receptor binds to acceptors on chromatin
(d) transcription process begins
(e) mRNA goes to rough ER for protein synthesis
Specifics of the AP and the Neuron
Conduction Velocity and Myelin
1) larger (diameter) axon = faster conduction
2) < 1 m/s for small, unmylenated neurons
3) > 50 m/s for large mylenated neurons
4) Myelin
(a) def: a segmented, non-conductive sheath surrounding the neuron
(b) No (few) ion channels underneath the sheath
(c) High concentration of ion channels at the breaks in the sheat: Nodes of Ranvier
(d) AP “jumps” from one node to the next
(e) Schwann Cells:
(i)
cells responsible for mylenation in the PNS
(ii)
each segment approx 1 mm
(f) Oligodendrocytes:
(i)
cells responsible for mylenation in the CNS
(ii)
each cell wraps several nerves
(iii)
also segmented with nodes
Neurotransmitters
1) Amino Acids
(a) aspartate, GABA (inhibitory), Glutamate (exitatory), Glycine
(b) only found in CNS
2) Monoamines
(a) Synthesized from Amino Acids
(b) widely active in the brain
(c) imbalances associated with mental disorders
(d) Catecholamines
(i)
dopamine – psychotic disorders, (nor)epinephrine
(e) Indolamines
(i)
seratonin – mood regulation, melatonin
3) Acetylcholine: first neurotransmitter discovered – CNS and all neuro-musular junctions
4) Soluable gasses: NO, CO
5) Peptides: endorphins
6) Steroids: derived from cholesterol
7) USAGE:
(a) Majority of neurons use GABA or Glutemate
(b) many different types of receptors for each transmitter
Sensory and Motor Systems
VIII) Sensory System Principles
A)
Specialized Receptors
1) nt receptors are replaced with chemical or mechanical motion-sensitive ion gates
2) Two types:
(a) slow adapting
(i)
sense stimulus for a longer period
(ii)
sense absolute levels of the stimulus
(b) fast adapting
(i)
sense stimulus CHANGES for a short period
(ii)
if stimulus does not change, may stop firing entirely
B)
Localization of Stimuli
1) there are 2 receptors for most sensors; by comparing the information from both receptors, brain can determine
relative direction, etc. of a stimulus (e.g., ears)
C)
Coding / Preprocessing
1) a large amount of information processing occurs before info arrives at cortex
2) hig compression: many sensors, few neursons
D)
Complex Neural Pathways
1) neuromuscular pathways are 1 –2 neurons
2) sensory pathways are 3-4 neurons: sensory systems can drive multiple centers
E)
THE SENSES: there are 8; 2 of which are subconscious
IX)
Vision
A)
vision occupies a greatern percentage of the human cortex than any other sense
B)
humans see electromagnetic radiation from 380 – 760 nm
C)
Gross Anatomy of the Eye
1) Cornea: protective layer over pupil
2) Lens: focuses light onto retina
3) Fovea: in line w/ straight ahead; only part of eye that has color receptors
4) Macula: area surrounding the fovea
5) optic disk: where retinal neurons group and leave eye – NO VISION HERE
D)
The Retina
1) Rods: hi-sensitivity BW vision
(a) night vision, slow adapting; not in fovea; 120 million
(b) only one opsin: Rhodopsin 498 nm (most sensitive at a blue-green color)
2) Cones: low-sensitivity color vision
(a) color vision; fast adapting; mostly in fovea; 6 million
(b) three opsins: Cyanolabe (blue), Chlorolabe (green), erythrolabe (red)
E)
The Neuronal Process of Vision
1) Na+ channels are normally open
F)
G)
X)
A)
B)
C)
D)
2) Single photon detected by disk
3) second messenger system closes Na+ channel, causing hyperpolarization
Retinal Processing
1) Receptors: graded potentials, gap junctions, hyperpolarize in light
2) Horizontal cells: inhibitory; connects across the retina horizontally, interacting with many receptor cells.
3) Biopolar cells: concentric oppositional surround response; 1:1 bypass for fovea only
4) Amacrine cells: seem to be responsive to changes
5) Ganglion cells: first to generate action potentials
(a) 800,000 outputs (150:1 for rods, 8:1 for cones)
(b) several different types respond differently to different aspects of stimuli (e.g., slow moving, fast moving,
orientation, etc.)
The Optic Tract
1) Retina  Optic Chiasm  LGN  cortex
2) Optic Chiasm: where the contralateral retinal hemispheres switch sides
(a) Right-half of retina goes to left half of brain
(b) Left-half of retina goes to right half of brain
3) LGN: 80% of optic nerve ends here
4) Superior Colliculi: 20% project here – outputs to ocular muscles, head and neck movements, and attention
5) Visual Cortex:
(a) V1: ocular dominance, oreintation sensitive; foveal area exaggerated
(b) V2: central 50% of visual field; comlex and simple cells. 80% of cells respond to ocular disparity (i.e.,
distance). electrical stimulation = hallucinations
(c) V3: shape and what? – almost entire field of view; prefers static and slow moving. shape discrimination
area
(d) V4: color and texture
(e) V5: Motion
(i)
Middle temporal cortex: motion 5 – 100 deg/sec across or toward/away from eye; some nerves
respond to particular speeds
(ii)
Inferotemporal cortex: respond to very specific shapes
(f) V6: Depth
Olfactory
sensitive to over 2000 oderants
operate by 2nd messenger using cAMP
project ipsilaterally onto cortex (like taste)
cilia  olfactory receptor neurons  glomeruli  olfactory nerve