Fundamentals of Anatomy & Physiology An Introduction To The Cellular Level of organization.
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Learning Objectives
• List the main points of the cell theory.
• Describe the chief structural features of the cell membrane.
• Describe the organelles of a typical cell, and give their specific functions.
• Summarize the process of protein synthesis.
• Describe the various transport mechanisms used by cells.
• Describe the cell life cycle, mitosis and cellular differentiation.
• Cells are the building blocks of all plants and animals
• Cells are produced by the division of preexisting cells
• Cells are the smallest units that perform all vital physiological functions
• Each cell maintains homeostasis at the cellular level
• Homeostasis at higher levels reflects combined, coordinated action of many cells
An Introduction to Cells
The cell theory states:
• Cytology, the study of the structure and function of cells
• The human body contains both somatic and sex cells
Cell biology
• Is surrounded by extracellular fluid, which is the interstitial fluid of the tissue
• Has an outer boundary called the cell membrane or plasma membrane
A typical cell
• Physical isolation
• Regulation of exchange with the environment
• Structural support
The Cell Membrane
Cell membrane functions include:
• The cell membrane is a phospholipid bilayer with proteins, lipids and carbohydrates.
The Cell Membrane
• Integral proteins
• Peripheral proteins
• Anchoring proteins
• Recognition proteins
• Receptor proteins
• Carrier proteins
• Channels
Membrane proteins include:
• Nonmembranous organelles are not enclosed by a membrane and always in touch with the cytosol
• Cytoskeleton, microvilli, centrioles, cilia, ribosomes, proteasomes
• Membranous organelles are surrounded by lipid membranes
• Endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria
Organelles
• Microfilaments
• Intermediate filaments
• Microtubules
• Thick filaments
Microvilli increase surface area
Cytoskeleton provides strength and flexibility
• Direct the movement of chromosomes during cell division
• Organize the cytoskeleton
• Cytoplasm surrounding the centrioles is the centrosome
Centrioles
• Are responsible for manufacturing proteins
• Are composed of a large and a small ribosomal subunit
• Contain ribosomal RNA (rRNA)
• Can be free or fixed ribosomes
Ribosomes
• Remove and break down damaged or abnormal proteins
• Require targeted proteins to be tagged with ubiquitin
Proteasomes
• Intracellular membranes involved in synthesis, storage, transportation and detoxification
• Forms cisternae
• Rough ER (RER) contains ribosomes
• Forms transport vesicles
• Smooth ER (SER)
• Involved in lipid synthesis
Endoplasmic reticulum
• Forms secretory vesicles
• Discharged by exocytosis
• Forms new membrane components
• Packages lysosomes
Golgi Apparatus
• Lysosomes are
• Filled with digestive enzymes
• Responsible for autolysis of injured cells
• Peroxisomes
• Carry enzymes that neutralize toxins
Lysosomes and Peroxisomes
• Continuous movement and recycling of membranes
• ER
• Vesicles
• Golgi apparatus
• Cell membrane
Membrane flow
• Responsible for ATP production through aerobic respiration
• Matrix = fluid contents of mitochondria• Cristae = folds in inner membrane
Mitochondria
• Surrounded by a nuclear envelope
• Perinuclear space
• Communicates with cytoplasm through nuclear pores
The Nucleus
The nucleus is the center of cellular operations
• A supportive nuclear matrix• One or more nucleoli• Chromosomes
• DNA bound to histones• Chromatin
Contents of the nucleus
• The cells information storage system
• Triplet code
• A gene contains all the triplets needed to code for a specific polypeptide
The genetic code
• Gene activation initiates with RNA polymerase binding to the gene
• Transcription is the formation of mRNA from DNA
• mRNA carries instructions from the nucleus to the cytoplasm
Gene activation and protein synthesis
• A functional polypeptide is constructed using mRNA codons
• Sequence of codons determines the sequence of amino acids
• Complementary base pairing of anticodons (tRNA) provides the amino acids in sequence
Translation is the formation of a protein
• The ease with which substances can cross the cell membrane
• Nothing passes through an impermeable barrier
• Anything can pass through a freely permeable barrier
• Cell membranes are selectively permeable
How Things Get Into and Out of Cells
Permeability
• Movement of a substance from an area of high concentration to low
• Continues until concentration gradient is eliminated
How Things Get Into and Out of Cells
Diffusion
• Diffusion of water across a semipermeable membrane in response to solute differences
• Osmotic pressure = force of water movement into a solution
• Hydrostatic pressure opposes osmotic pressure
• Water molecules undergo bulk flow
How Things Get Into and Out of Cells
Osmosis
• The effects of osmotic solutions on cells
• Isotonic = no net gain or loss of water
• Hypotonic = net gain of water into cell
• Hemolysis
• Hypertonic = net water flow out of cell
• Crenation
Tonicity
• Carrier mediated transport
• Binding and transporting specific ions by integral proteins
• Cotransport
• Counter-transport
• Facilitated diffusion
• Compounds to be transported bind to a receptor site on a carrier protein
transport
• Active transport
• Consumes ATP
• Independent of concentration gradients
• Types of active transport include
• Ion pumps
• Secondary active transport
Active transport
• Endocytosis is movement into the cell
• Receptor mediated endocytosis (coated vesicles)
• Pinocytosis
• Phagocytosis (pseudopodia)
• Exocytosis is ejection of materials from the cell
Vesicular transport: material moves into or out of cells in membranous vesicles
• Difference in electrical potential between inside and outside a cell
• Undisturbed cell has a resting potential
The transmembrane potential
• Cell division is the reproduction of cells
• Apoptosis is the genetically controlled death of cells
• Mitosis is the nuclear division of somatic cells
• Meiosis produces sex cells
The Cell Life Cycle
cell division
• Most somatic cells spend the majority of their lives in this phase
• Interphase includes
• G1
• S
• G2
The Cell Life Cycle
Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase
Mitosis, or nuclear division, has four phases
During cytokinesis, the cytoplasm divides and cell division ends
• Generally, the longer the life expectancy of the cell, the slower the mitotic rate
• Stem cells undergo frequent mitoses
• Growth factors can stimulate cell division
• Abnormal cell division produces tumors or neoplasms
• Benign
• Malignant (invasive, and cancerous)
• Spread via metastasis
• Oncogenes
Mitotic rate and cancer
• Process of specialization
• Results from inactivation of particular genes
• Produces populations of cells with limited capabilities
• Differentiated cells form tissues
Differentiation
• The main points of the cell theory.
• The chief structural features of the cell membrane.
• The organelles of a typical cell, and their specific functions.
• The process of protein synthesis.
• The various transport mechanisms used by cells, and how this relates to the transmembrane potential.
• The cell life cycle, mitosis and cellular differentiation.
You should now be familiar with:
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