Cell Organelles and Characteristics of Life

Organelles

• Organelles are specialized structures within cells performing specific functions
• Nucleus: Stores genetic information, controls cell activities (growth, metabolism, protein synthesis)
• Mitochondria: Generate energy (ATP) through cellular respiration
• Ribosomes: Synthesize proteins
• Endoplasmic Reticulum (ER): Transports proteins and materials; smooth ER synthesizes lipids; rough ER synthesizes proteins
• Golgi Apparatus: Modifies, sorts, and packages proteins for secretion or delivery
• Lysosomes: Break down waste materials and cellular debris
• Peroxisomes: Break down fatty acids and detoxify harmful substances
• Cytoskeleton: Maintains cell shape, facilitates movement within the cell

Characteristics of Life

• An organism is considered alive if it demonstrates these characteristics
• Metabolism: Chemical reactions (catabolic and anabolic) for life maintenance
• Reproduction: Ability to reproduce and pass on genetic material
• Circulation: Movement of substances (nutrients, gases, waste) throughout the organism
• Digestion: Breakdown of food into simpler molecules for absorption
• Ingestion: Taking in food and liquids
• Absorption: Uptake of nutrients into cells or tissues
• Excretion: Removal of waste products from the body

Other Important Concepts

• Homeostasis: Maintaining a stable internal environment despite external changes (temperature regulation, pH balance, blood sugar regulation)

Planes of the Body

• Transverse Plane: Divides the body into upper and lower parts
• Sagittal Plane: Divides the body into right and left halves
• Frontal (Coronal) Plane: Divides the body into front and back portions

Muscle Tissue

• Skeletal Muscle: Voluntary, striated muscle used for moving bones
• Cardiac Muscle: Involuntary, striated muscle found in the heart with intercalated discs
• Smooth Muscle: Involuntary, non-striated muscle in organ walls (intestines, blood vessels), responsible for involuntary movements like peristalsis

Skeletal Muscle Contractions

• Motor Unit: A motor neuron and all muscle fibers it controls (stronger contraction = more fibers)
• Types of Contractions:
  • Isometric: Muscle contracts but doesn't change length
  • Isotonic: Muscle changes length during contraction (concentric - shortening, eccentric - lengthening)
• Motor Unit Definition: Functional unit of muscle contraction, consisting of a single motor neuron and the muscle fibers it innervates
• Neurological and Physiological Components: Motor neurons transmit signals from the central nervous system to muscle fibers triggering muscle contraction

Muscle Movement

• Myofibril: Long, threadlike structures within muscle fibers containing sarcomeres (contractile units)
• End Plate: Where a motor neuron connects with a muscle fiber (part of the neuromuscular junction)
• Motor Neuron: Transmits signals from the central nervous system to the muscle
• Actin & Myosin: Filaments within the sarcomere for muscle contraction (Myosin binds to Actin to move and create contractions)
• Chemicals: Acetylcholine, Calcium ions, and ATP are critical for muscle contraction
• Agonist: Prime mover in muscle contraction
• Antagonist: Muscle that opposes the agonist's action
• Recruitment: More motor units recruited to generate more force as load increases
• Origin: Fixed attachment point of a muscle to a bone
• Insertion: Movable attachment point of a muscle to a bone

Sarcomere

• Structure and Function: Smallest functional unit of muscle contraction, composed of actin and myosin filaments
• Summation: Repeated stimuli result in stronger contractions (potentially tetanic contraction)

Layers of Skeletal Muscle

• Epimysium: Outer layer surrounding the whole muscle
• Perimysium: Surrounds individual fascicles (bundles of muscle fibers)
• Endomysium: Surrounds individual muscle fibers

Periods of a Muscle Twitch

• Latent Period: Time between stimulus and contraction onset
• Contraction Period: Time during muscle contraction
• Relaxation Period: Time during muscle relaxation

Steps in Muscle Contraction

• Neural signal (action potential) activates the muscle
• Acetylcholine released, triggers action potential
• Calcium released from sarcoplasmic reticulum, exposes binding sites on actin
• Cross-bridge formation between myosin and actin
• Power stroke occurs, causing muscle contraction (myosin moves actin)
• Myosin heads detach, reattach for continued contraction (cross-bridge cycling)
• Muscle relaxes when neural signal stops, calcium pumped back into sarcoplasmic reticulum

Cross-Bridging

• Steps in cross-bridging (detailed steps of the molecular process of muscle contraction)

Enzymes in Muscle Contraction

• Acetylcholinesterase: Breaks down acetylcholine to stop stimulation
• Myosin ATPase: Hydrolyzes ATP for power stroke energy
• Creatine Kinase: Regenerates ATP during short bursts of activity
• Phosphofructokinase (PFK): Catalyzes glycolysis to produce ATP from glucose
• Myokinase: Converts ADP to ATP during intense exercise
• Calcium ATPase (SERCA): Pumps calcium back into the sarcoplasmic reticulum for muscle relaxation
• Troponin C: Binds calcium, initiates muscle contraction by exposing actin-myosin binding sites

Skeleton

• Skeletal Regeneration: Process of blood cell production (10 years)
• Hematopoiesis: Formation of blood cells in red bone marrow (red blood cells, white blood cells, platelets)

Explore the key cell organelles and their functions, along with the essential characteristics that define life. This quiz will test your knowledge about the different structures within cells and how they contribute to the maintenance of life processes.