Biochem test 3

Neuron Structure

Soma, Dendrites, Axon, Myelin Sheath, Nodes of Ranvier, Axon Terminal

Cell body(soma)

contains nucleus

Dendrites

Receive signals

Axon

carries signals away from cell

Myelin Sheath

Insulation that speeds signal conduction

Nodes of ranvier

Gaps in myelin allowing faster transmission

Axon terminal

releases neurotransmitters

Types of nerve cells

Motor Neurons, Sensory Neurons, Interneurons

Motor neurons

carry signals from CNS to muscle

Sensory neurons

Send info from body to CNS

Interneurons

Connects neurons within CNS

Myelin Producing cells in CNS

Oligodendrocytes

Myelin producing cells in PNS

Schwann cells

Resting membrane potential

Electrical charge difference across membrane (-70mV)

What is resting membrane potential caused by

Na+ mostly outside cell, K+ mostly inside (Na+/K+ pump uses ATP to maintain gradient.

Steps of an action potential

1)Resting state, 2)Depolarization, 3)Threshold reached, 4)repolarization, 5)Hyperpolarization, 6)signal travels along neuron by propagation

1)Resting state of an action potential

Na+ outside, K+ inside

2)Depolarization of an action potential

Na+ channels open, Na+ rushes into cell

3)What happens when the threshold is reached in an action potential

The action potential is triggered

4)repolarization of an action potential

K+ leaves the cell

5) Hyperpolarization

Membrane becomes slightly more negative than resting

6) how does the signal travel along the neuron

Propagation

Neuromuscular junction

Where the motor neuron communicates with the muscle fiber

How many steps are in neuromuscular junction?

6

step 1 of the neuromuscular junction

Action potential reaches axon terminal

step 2 of the neuromuscular junction

Ca2+ enters the neuron

step 3 of the neuromuscular junction

Vesicles release acetylcholine(ACh)

step 4 of the neuromuscular junction

ACh binds receptors on muscle membrane

step 5 of the neuromuscular junction

Muscle cell depolarizes

step 6 of the neuromuscular junction

Muscle contraction begins

What is ACh broken down by in the neuromuscular junction?

Acetylcholinesterase

When does muscle fatigue occur?

When ATP only drops about 20-30%

Causes of muscle fatigue

decreased ATP availability, Accumulation of Pi and ADP, Impaired Ca2_ release from sarcoplasmic reticulum, reduced neural stimulation, accumulation of metabolites(H+/lactate)

Muscle fiber components

Sarcolemma, Sarcoplasm, Myofibrils, Sarcomere

Sarcolemma

Muscle cell membrane

Sarcoplasm

Cytoplasm of muscle cell

Myofibrils

Contractile structures

Sarcomere

Functional unit of muscle

Sarcomere structure

Z-line, I band, A band, H zone, M line

Z-line

boundary

I band

Light region(actin only)

A band

Dark region (actin + myosin)

H zone

Myosin only

M line

Center structure

Sarcomere proteins

Actin(thin filament), Myosin(thick filament), Titin(elasticity), Nebulin(stabilizes actin)

sliding filament theory

Muscle shortens when acting slides past myosin

Sarcomere shortens but filaments do not change length

Sliding filament theory steps

1)Myosin binds acting 2)Myosin pulls actin inward 3)Sarcomere shortens 4)Force is produced

Properties of myosin

Motor protein, has head that binds actin, contains ATPase enzyme, Converts ATP→ mechanical energy

Properties of Actin

Thin filament, Contains binding sites for myosin, G-actin(globular), F-actin(fibrous)

Cross bridge attachment/Power stroke

1)myosin head binds actin(cross bridge attachment) 2) Power stroke pulls actin3)ATP binds to myosin breaking the actin off 4) ATP hydrolyzed→Myosin resets

When is ATP vital in the cross bridge/power stroke?

In order to detach the myosin head, energy for next contraction. No ATP=Muscle stiffness.

Excitation-contraction coupling

Links nervous system to muscle contraction

Steps of excitation-contraction coupling

1Action potential travels down T-tubules,2Sarcoplasmic reticulum releases Ca2+, 3)Ca2+ binds with troponin(TnC), 4) Tropomyosin shifts, 5)Myosin binding sites exposed, 6)Contraction occurs

Where is the calcium returned after contraction occurs?

The calcium pump (Ca2+ ATPase) returns the Ca2+ to the sarcoplasmic reticulum

Functions that degrade ATP

Muscle contraction, active transport, Biosynthesis, signal transduction, DNA replication, Calcium transport

ATP hydrolysis degrades ATP formula

ATP→ ADP + Pi + energy

ATP stores/regulations

6mmol per kg muscle, must be continuously resynthesyzed, ATP turnover is high(-45kg/day) Tightly regulated to prevent rigor

Adenylate kinase reaction formula

2ADp→ ATP + AMP

Enzyme for adenylate Kinase reaction

adenylate kinase (myokinase)

AMP accumulation signals need for more ATP production

When does the Adenylate kinase reaction occur?

When ATP demand is high

ATP-Pcr system

it is an immediate energy system for short high intensity exercise(0-15 seconds)

anaerobic, fast ATP production, limited capacity, used during sprinting/heavy lifting

ATP-Pcr System formula

PCr + ADP → ATP + Cr

Enzymes in Glycogenesis by step

1)Hexokinase/Glucokinase(Glucose→Glucose 6-phosphate)

2)Phosphoglucomutase(G6P→G1P)

3)UDP-glucose pyrophosphorylase(G1P→UDP-glucose)

4)Glycogen synthase(chain elongation)

5) Branching enzymes(branching)

Purpose of Glycogenesis

Store glucose for later energy

Glycogenolysis purpose

Breakdown glycogen into glucose for energy production

occurs when exercise begins, blood glucose is low, muscle needs ATP quickly

Liver Glycogenolysis

G6P is converted to glucose to maintain blood sugar

Muscle glycogenolysis

G6P enter glycolysis

Glycogenolysis enzymes by step

1)glycogen phosphorylase(Glycogen→G1P)

2)Debranching enzyme(branch removal)

3)Phosphoglucomutase(G1P→G6P)
4)Glucose-6-phosphatase(liver only)

Regulation enzymes for Glycogenolysis

Phosphorylase kinase, Phosphorylase phosphatase(PP1)

Glycolysis formual

Glucose→ 2 Pyruvate + ATP + NADH

Glycolysis imprtant enzymes

Hexokinase, PFK-1(rate limiting), Pyruvate kinase, Lactate dehydrogenase(pyruvate→lactate)

Glycolysis purpose

Converts glucose→pyruvate

What does glycolysis produce?

2 ATP, 2NADH

PFK regulation in glycolysis

inhibited by ATP, Activated by AMP and ADP

CAC Formula

AcetylCoa→ CO2 + NADH + FADH2 + ATP

Citric Acid Cycle (mitochondria) purpose

Remove electrons for the ETC

Key enzymes in the CAC

Citrate synthase, Isocitrate dehydrogenase, Alpha-ketoglarate dehydrogenase,

Succinate dehydrogenase

what does the CAC produce

NADH, FADH2, CO2

ETC Formula

NADH + FADH2 + O2 → ATP + H2O

ETC purpose

Uses NADH and FADH2 to produce ATP

How many Complexes are in the ETC

I-IV, final step is ATP synthase

Important cofactors of CAC

FMN, FAD, Coenzyme Q, Cytochrome C

What is the final electron acceptor in the ETC

Oxygen

ATP yield from NADH within ETC

2.5 ATP

ATP yield from FADH2 within ETC

1.5 ATP

Lactate formation (anaerobic metabolism) Purpose

Regenerate NAD+ so glycolysis can continue producing ATP when oxygen is limited

Pyruvate → Lactate

When does lactate formation occur

high intensity exercise

Pyruvate oxidation purpose

Convert into acetyl Coa so it can enter the CAC

occurs in mitochondria

What does pyruvate oxidation produce?

NADH and Acetyl CoA connects glycolysis to aerobic metabolism

ways to control metabolism

Allosteric regulation, covalent modification, substrate availability, hormonal regulation

Alosteric regulation

Molecule binds to a site on an enzyme other than the active site. Becomes more or less active

EX: AMP activates PFK

Covalent Modification

Adding or removing chemical groups

EX: phosphorylase activated

Substrate availability

Reaction speed depends on how much substrate is available

EX: more glucose increases glycolysis

Hormonal regulation

Hormones binds receptors and trigger signaling pathways that change enzyme activity

EX:epinephrine increases glycogen breakdown

Regulations of Glycogenolysis

It is controlled by phosphorylase kinase, phosphorylase a, phosphorylase b

phosphorylase a is activated during exercise

physiological triggers (Pi, AMP, Ca++) and how they regulate glycogenolysis.

Pi: ATP breakdown increases Pi stimulating glycogen breakdown

AMP: as AMP increases it signals low energy activating glycogen phosphorylase

Ca2+: Ca2+ is released during contraction activating phosphorylase kinase via calmodulin

cAMP second messenger system + glycogenolysis

1)Epinephrine is released through the medulla and binds to a B-andrenergic receptor. 2) The receptor activates a G-protein to pass the signal inside the cell. 3) G protein activates adenylate cyclase within the cell membrane. 4) Adenylate cyclase converts ATP → cAMP which increases quickly during exercise. 5) cAMP activates PKA. 6)PKA activates phosphorylase kinase activating glycogen phosphorylase. 7) Glycogen phosphorylase converts glycogen → G1P and glucose enters glycolysis to produce ATP.

How does PFK affect Glycolysis?

It is a rate limiting enzyme activated by ADP, AMP, Pi, and inhibited by ATP and Citrate

How does Pyruvate Kinase affect Glycolysis

the final step in glycolysis to convert PEP into pyruvate to produce ATP, helps determine how quickly it proceeds. activated by ADP and inhibited by ATP

How does lactate dehydrogenase affect Glycolysis

regenerate NAD+ so glycolysis can continue producing ATP under anaerobic conditions.