Human Anatomy and Physiology Chapter 3

The Cell

the basic, living, structural, and functional unit of the body.

Cytology

The study of cell structure

Cell Physiology

The study of cell function

Cells three principal parts

Plasma (Cell) membrane, cytoplasm (cytosol, organelles except for the nucleas) nucleus

Plasma Membrane

A flexible, sturdy barrier that surrounds and contains the cytoplasm of the cell. 50% lipid and 50% protein. Held together by hydrogen bonds. Lipid is barrier to entry/exit of polar substances. Proteins are gatekeepers which regulate traffic. 50 Lipid molecules for each protein molecule.

Lipid Bilayer

the basic framework of the plasma membrane and is made up of three types of lipid molecules: Phospholipids, cholesterol and glycolipids

The bilayer arrangement

occurs because the lipids are amphipathic molecules. They both have polar (charged) and nonpolar (uncharged) parts with the polar “head of the phospholipid pointing out the nonpolar “tail” pointing towards the center of the membrane.

Cholesterol molecules

weakly amphiphotic and are interspersed among other lipids

Glycolipids

appear only in the membrane layer which faces the extracellular fluid

Phospolipids

comprises 75% of lipids, the bilayer= 2 parallel layers of molecules. each molecule is amphipathic (has both a polar and nonpolar region)

Polar parts (Heads)

are hydrophilic and face on both surfaces a watery environment

nonpolar parts (tails)

are hydrophobic and line up next to each other in the interior

Cholesterol within the cell membrane

comprises 20% of cell membrane lipids, interspersed among the other lipids in both layers, stiff steroid rings and hydrocarbon tail are nonpolar and hide in the middle of the cell membrane.

Glycolipids within the cell membrane

Comprises 5% of the lipids of the cell membrane, carbohydrate groups form a polar head only on the side of the membrane facing the extracellular fluid

Arrangment of membrane proteins

divided into integral and peripheral proteins.

Integral Proteins

Are amphipathic. Many are glycoprotiens. Extend into or across the entire lipid bilayer among the fatty acid tails of the phospholipid molecules. The combined glycoproteins and glycolipids form the
glycocalyx which helps cells recognize one another, adhere to one another, and be protected from digestion by enzymes in the extracellular fluid

Peripheral Proteins

are found at the inner or outer surface of the membrane and can be stripped away from the membrane without disturbing membrane integrity

Membrane Proteins

Membrane proteins vary in different cells and functions as channels (pores), transporters, receptors, enzymes, cell- identity markers, and linkers. The different protiens help to determine many of the functions of the plasma membrane

Functions of Membrane Proteins

Formation of channel, Transporter Proteins, Receptor Protiens, Cell identity Marker, Linker, Act as Enzyme

Formation of Channel

Passageway to allow specific substance to pass through

Transporter Proteins

Bind a specific substance, change their shape and move it across membrane

Receptor protiens

Cellular recognition site, bind to substance

Cell Identity Marker

Allow cell to recognize other similiar cells

Linker

Anchor proteins in cell membrane or to other cells, allow cell movement, cell shape and structure

Act as Enzyme

Speed up reactions

Membrane Fluidity

Membranes are fluid structures, rather like cooking oil, because most of the membrane lipids and many of the membrane proteins easily move in the bilayer. Membrane lipids and proteins are mobile in their own half of the bilayer. Cholesterol serves to stabilize the membrane and reduce membrane fluidity.

Membrane Permeability

Plasma membranes are selectively permeable (some things can pass through, some cant). The lipid bilayer portion of the membrane is permeable to small, nonpolar, uncharged molecules but impermeable to ions and charged or polar molecules. The membrane is also permeable to water. Transmembrane proteins that act as channels or transporters increase the permeability of the membrane to molecules that cannot cross the lipid bilayer. Macromolecules are unable to pass through the plasma membrane except by vesicular transport.

Concentration Gradient

is the difference in the concentration of a chemical between one side of the plasma membrane and the other. Oxygen and sodium ions are more concentrated outside the cell membrane with carbon dioxide and potassium ions more concentrated inside the cell membrane.

Electrical Gradient

The inner surface of the membrane is more negatively charged and the outer surface is more positively charged, this sets up what is also known as a membrane potential. Maintaining the gradients are important to the life of the cell.

Electrochemical Gradient

Combined concentration and eletrical gradients.

Transport across the plasma membrane

processes to move substances across the cell membrane are essential to the life of the cell. Some substances cross the lipid bilayer while others cross through ion channels. Transport processes that mover substances across the cell membrane are either active or passive.

Types of Passive Processes

Diffusion through lipid bilayer, diffusion through ion channels, faciliated diffusion. Active transport requires cellular energy. Materials can also enter or leave the cell through vesicle transport.

Substances cross membranes by a variety of processes

mediated transport moves materials with the help of a transporter protein, nonmediated transport does not use a transporter protein, active transport uses ATP to drive substances against their concentration gradients, passive transport moves substances down their concentration gradient with only their kinetic energy, vesicular transport move materials across membranes in small vesicles -- either by, exocytosis or endocytosis

Diffusion

the random mixing of particles that occurs in a solution as a result of the kinetic energy of the particles.

Diffusion rate across plasma membranes is influenced by several factors

Steepness of the concentration gradient, temperature, size or mass of the diffusing substance, surface area, diffusion distance.

Diffusion through the lipid bilayer

Nonpolar, hydrophobic molecules such as respiratory gases, some lipids, small alcohols and ammonia can diffuse across the lipid bilayer. It is important for gas exchange, absorption of some nutrients, and excretion of some wastes.

Diffusion through Membrane Channels

Most membrane channels are ion channels, allowing passage of small, inorganic ions which are hydrophilic. Ion channels are selective and specific and may be gated or open all the time.

Osmosis

The net movement of a solvent through a selectively permeable membrane, or in living systems, the movement of water (the solute) from an area of higher concentration to an area of lower concentration across the membrane. Water penetrates membrane by diffusion through lipid bilayer or through aquaporins. Water moves to lower concentration to an area of higher solute concentration. Only occurs when the membrane is permeable to water but not to certain solutes.

Tonicity

A measure of solutions ability to change the volume of cells by altering their water concentration

Isotonic Solution

Red blood cells maintain their normal shape

Hypotonic Solution

Red blood cells undergo hemolysis

Hypertonic Solution

red blood cells undergo cremation

Facilitated Diffusion

A solute binds to a specific transporter on one side of the membrane and is released on the other side after the transporter undergoes a conformational change. Those solutes move across membranes. include glucose, urea, fructose, galactose, and some vitamins. The rate of the movement depends on steepness of concentration gradient, number of transporter proteins.

Transport Maximum

The upper limit on the rate at which facilitaed diffusion can occur. If all the transporters are occupied, then the rate of facilitated diffusion does not increase. Glucose enters the cell by facilitated diffusion.

Facilitated Diffusion of Glucose

Glucose binds to transport protein, transport protein changes shape. Glucose moves across cell membrane (but only down the concentration gradient) Kinase enzyme reduxes glucose concentration inside the cell by transforming glucose into glucise-6-phosphate. Transporter proteins always bring glucose into cell

Active Transport

an energy-requiring process that moves solutes such as ions, amino acids, and monosaccharides against a concentration gradient.

Primary Active Transport

Energy derived from ATP changes the shape of a transporter protein, which pumps a substance across the plasma membrane against its concentration gradient. Most prevalent mechanism is the sodium ion/ potassium ion pump. Requires 40% of cellular ATP, all cells have 1000’s of them. Maintains low concentration of NA+ and a high concentration of K+ in the cytosol, operates continually.

Cystic Fibrosis

Caused by a defective gene that produces an abnormal chloride ion transported. The disease affects the respiratory, digestive, urinary, and reproductive systems.

Secondary Active Transport

The energy stored in the form of a sodium or hydrogen ion concentration gradient is used to drive other substances against their own concentration gradients. Plasma membranes contain several antiporters and symporters powered by the sodium ion gradient.

Digitalis

Slows the sodium ion-calcium ion antiporters, allowing more calcium to stay inside heart muscle cells, which increases the force of their contraction and thus strengthens the heartbeat

Vesicles

A small membranous sac formed by a budding off from an existing membrane.

Endocytosis

Bringing something into the cell, materials move into a cell in a vesicle formed from the plasma membrane.

Phagocytosis

Cell eating by macrophages and WBC’s, Particle binds to receptor protein, whole bacteria or viruses are engulfed and later digested. the ingestion of solid particles. pseudopods extend to form phagosome.

Pinocytosis

Cell drinking, cell receptor problems, the ingestion of extracellular fluid. No pseudopods form, nonselective drinking of extracellular

Exocytosis

Release something from the cell. Veiscles form inside cell, fuse to cell membrane, release their contents, digestive enzymes, hormones, neurotransmitters or waste products. Replace cell membrane lost by endocytosis

Receptor-mediated Endocytosis

the selective uptake of large molecules and particles by cells. Steps include binding, vesicle formation, uncoating, fusion with endosome, recycling of receptors, and degradation in lysosomes. Viruses can take advantage of this to enter cells.

Secretory Vesicles

form inside the cell fuse with plasma membrane and release their contents into the extracellular fluid

Transcytosis

may be used to move a substance into across and out of a cell

Cytosol

The intracellular fluid, is the semifluid portino of cytoplasm that contains inclusions and dissolved solutes. Mostly composed mostly of water, plus protiens, carbohydrates, lipids, and inorganic substances. The chemicals are either in solution or in a colloidal (suspended form) the medium in which many metabolic reactions occur

Organelles

specialized structures that have characteristic shapes and perform specific functions in cellular growth, maintenance and reproduction. Often cooperate to maintain homeostasis.

Cytoskeleton

Network of protein filaments throughout the cytosol, functions, cell support and shape, organization of chemical reactions, cell and organelle movement. continually reorganized. Consist of microfilaments, intermediate filaments, and microtobules

Microfilaments

Most are composed of actin and function in movement and mechanical support and are most prevalent at the edge of the cell.

Intermediate filaments

Are exceptionally strong, found in parts of cells subject to mechanical stress; they help stabilize the position of organelles such as the nucleus and help attach cells to one another.

Microtubules

Are composed of a protein called tubulin and help determine cell shape and function in the intracellular transport of organelles and the migration of chromosome during cell division.

Centrosomes

Are dense ares of cytoplasm containing the centrioles, whih are paired cylinders arranged at right angles to one another, and serve as centers for organizing microtubules in interphase cells and the mitotic spindle during cell division

Cilia

numerous, short, hairlike projections extending from the surface of a cell and functioning to move materials across the surface of the cell. Each cilium contains a core of 20 microtubules

Flagella

Are similiar to cilia but are much longer, usually moving an entire cell, the only example in the human body is the sperm cell tail. Generates forward motion along its axis by rapidly wiggling in a wavelike pattern.

Structure of Cilia and Flagella

Pairs of microtubules (9+2 array) covered by cell membrane, basal body is centriole responsible for initiating its assembly

Differences in CIlia and Flagella Structure

Cilia- Short and multiple Flagella- longer and single

Cilia Movement

Stiff during power stroke but flexible during recovery, many coordinated together, airways and uterine tube.

Flagella Movement

Single flagella wiggles in a wavelike pattern, propels sperm forward

RIbosomes

tiny spheres consisting of a ribosomal RNA and several ribosomal proteins; they occur free (singly or in clusters) or together with endoplasmic reticulum. The sites of protein synthesis. Composed of Ribosomal RNA and Protein.

Membrane- Bound Ribosomes

Attached to endoplasmic reticulum or nuclear membrane, synthesize proteins needed for plasma membrane or for export. 10-20 together form a polyribosome

Ribosomal subunits

Large+ small subunits, made in the nucleolus, assembled in the cytoplasm

Endoplasmic Reticulum

Network of membranes that form flattened sacs or tubules called cisterns, transports substances, stores newly, synthesized molecules, synthesizes and packages molecules, detoxifies chemicals, and releases calcium ions involved in muscle contraction

Rough Endoplasmic Reticulum

Synthesizes glycoproteins and phospholipids that are transferred into cellular organelles, inserted into the plasma membrane, or secreted during exocytosis.

Smooth Endoplasmic Reticulum

extends from the rough ER to form a network of membrane tubules but does not contain ribosomes on its membrane surface. Detoxifies Drugs, repeated exposure to certain drugs produces changes to the smooth ER in the liver which results in tolerance to the drug.

Golgi Complex

Consist of three to twenty stacked, flattened membranous sacs. (cisterns) referred to as cis, medial, and trans. The principal function is to process, sort, and deliver proteins and lipids to the plasma membrane, lysosomes, and secretary vesicles.

Lysosomes

Membrane-enclosed vesicles that contain powerful digestive enzymes. Digest foreign substances, autophagy (autophagosome forms) recycles own organelles.

Tay-sachs Disorder

Affects children of eastern European- Ashkenazi descent, seizures, muscle rigidity, blind, demented, and dead before the age of 5. Genetic disorder caused by absence of single lysosomal enzyme. Enzyme normally breaks down glycolipid commonly found in nerve cells. as glycolipid accumulates, nerve cells lose functionality. Chromosome testing now available.

Perioxosomes

Similiar in structure to lysosomes, but are smaller. They contain enzymes that use molecular oxygen to oxidize various organic substances. art of normal metabolic breakdown of amino acids and fatty acids, oxidizes toxic substances such as alcohol and formaldehyde, contains catalase which decomposes H2O2

Proteosomes

Structures that destroy unneeded, damaged, or faulty proteins. they contain proteases which cut proteins into a small peptides. Are thought to be a factor in several diseases.

Mitochondria

is bound by a double membrane, the outer membrane is smooth with the inner membrane arranged in folds called cristae. The site of ATP production in the cell by the catabolism of nutrient molecules. self-replicates using their own DNA. Mitochondrial DNA (genes) are usually inherited only from the mother.

Mitochondrial Myopathies

inherited muscle disorders resulting from fualty mitochondrial genes. As a reuslt muscles become weak and fatigued easily.

Nucleus

usually the most prominent feature of a cell, most bodies have a single nucleus, some (red blood cells) have none, others (skeletal muscle) have several. Parts include nuclear envelope, which is perforated by channels called nuclear pores, nucleoli, and genetic material. Within is the Cell’s Hereditary units (genes) arranged in single file

Function of Nucleus

46 Human DNA molecules or chromosomes, genes found on chromosomes, gene is directions for a specific protein. Non-dividing cells contain nuclear chromatin, loosely packed DNA, Dividing cells contain chromosomes, tightly packed DNA, it doubled (copied itself) before condensing.

Chromosomes

Each is a long molecule of DNA that is coiled together with several proteins. Human somatic cells have 46 chromosomes arranged in 23 pairs. The various levels of DNA packing are represented by nucleosomes, chromatin fibers, loops, chromatids, and chromosomes.

Genomics

the study of the relationships between the genome and the biological functions of an organism. At least half consist of repeated sequences that do not code for proteins. Genomic medicine hopes to design drugs to treat genetic diseases.

Protein Synthesis

the biological process whereby amino acids are assembled by peptide bonding into specific polypeptide sequences in accord with genetic blueprints encoded by deoxyribonucleic acid (DNA)

Transcription

The process by which genetic information encoded in DNA is copied onto a strand of RNA called messenger RNA (mRNA) which directs protien synthesis. Transcription of DNA is catalyzed by RNA polymerase.

Transcription steps

1. DNA Sense strand is template for the creation of messenger RNA Strand

2. begins at promoter sequence where RNA polymerase attaches.

3. When RNA polymerase reaches the terminator sequence it detaches and transcription stops.

4. Pre-mRNA contains intron region that are cut out by enzymes.

5. Exon regions of mRNA will code for segments of the protein.

Translation

the process of reading the mRNA nucleotide sequence to determine the amino acid sequence of the protein. sequence of nucleotides on mRNA is ‘read’ by rRNA to construct a protein. (3 nucleotide sequences on mRNA are called codons.) specific tRNA molecule carry specific amino acids. Anticodons on tRNA are matched to specific codons on mRNA so proper amino acids can be strung together to create a protein molecule.

Translation sequence

1. initiator tRNA attaches to a start codon

2. L/S ribosomal subunits join to form a functional ribosome and initiator tRNA fits into P site

3. Anticodon of incoming tRNA pairs with next mRNA codon at A site.

4. Amino acid on tRNA at P site forms a peptide bond with amino acid at A site.

5. tRNA at P site leaves ribosom, ribosome shifts by one codon; tRNA previouslt at A site is now at the P site.

6. Protein synthesis stops when the ribosome reaches stop codon on mRNA

Cell division

the process by which cells reproduce themselves. It consists of nuclear division (mitosis and mieosis) and cytoplasmic division (cytokinesis)

Somatic Cell division

Cell division that results in an increase in body cells and involves a nuclear division called mitosis, plus cytokinesis.

Reproductive Cell Division

Cell division that results in the production of sperm and eggs. Consists of a nuclear division called Meiosis plus cytokinesis.

Cell cycle

is an orderly sequence of events by which a cell duplicates its contents and divides in two. It consists of interphase and the mitotic phase

Human Somatic Cells

contains 46 Chromosomes or 23 pairs of chromosomes

Homologous Chromosomes

Two chromosomes that make up a chromosome pair.

Diploid Cell

A cell with a full set of chromosomes