Anatomy and Physiology: Cell communication and metabolism

DNA Replication

Takes place in the nucleus, happens when cells are getting ready to divide

Initiation: two complementary strand of DNA are separated by DNA helicase

Elongation: DNA polymerase will bind to the leading and lagging strands and bring in correct bases to complement each template strand

Termination: stops once a new complementary strand is complete

Transcription

Takes place in the nucleus, happens when genes need to be expressed

Initiation: RNA polymerase binding to a region of DNA called the “promoter”

Elongation: RNA polymerase unwinds the DNA segment, aligns correct nucleic acid with its complementary base

Termination: terminator sequence of nucleotides causes transcription to stop and new mRNA folds up on itself

Before mRNA is complete, splicosome needs to remove introns and cap and tail needs to be added

Translation

Takes place in the cytoplasm, converts RNA to protein

Initiation: mRNA binds to a ribosome in the cytosol

Elongation: tRNA anticodons bind to codons in mRNA and begin linking peptides together

Termination: final codon on mRNA provides a stop message

Codon

3 base sequence of mRNA that directly encodes a specific amino acid

Diffusion

solute molecules move from high concentration to low concentration

Osmosis

solvent molecules (water) move from low solute concentration to high solute concentration

Isotonic

two solutions have the same concentration of solutes, no water movement

Hypertonic

solution that has higher concentration of solutes than another, water will rush out of cell and cells will shrink

Hypotonic

solution has a lower concentration of solutes than another, water will rush into cell and cells will swell and maybe burst

Factors that impact diffusion across the lipid bilayer

1. concentration gradient

2. mass of molecules

3. temperature

4. solvent density

5. solubility of solute

Passive transport

movement of substances across membrane without expenditure of energy

Concentration gradient

difference in concentration of a substance across a space

Facilitated diffusion

used for substances that cannot cross the lipid bilayer unassisted due to their size/charge/polarity, membrane transport proteins

Channel proteins

forms a pore, discriminates based size and charge

Transporter proteins

Transport molecules that fit into the binding site, undergoes a conformational change

Active transport

movement of cells across membrane using ATP

Sodium potassium pump

transports molecules against the concentration gradient, uses energy from ATP to drive accumulation of K+ in the cell and N+ outside the cell

Endocytosis

cell digs material by enveloping it into a portion of its cell membrane, contents become an independent vesicle

Exocytosis

cell exports material using vesicular transport, vesicle membrane fuses with cell membrane and contents are released

Phagocytosis

cell engulfs large, solid particles, "cell eating", extends membrane outward, form of endocytosis

Pinocytosis

uptake of extracellular fluid containing small dissolved molecules, "cell drinking", folds membrane inward, form of endocytosis

Electrochemical gradient

combined concentration gradient and electrical charge that affects an ion

electrogenic pump

pump that creates a charge imbalance, sodium potassium pump

Ligand

molecule that binds to another specific molecule while delivering a signal in the process, interacts with protein receptors in target cells

Paracrine signaling

cell targets a nearby cell

Example: transfer of signals across synapses between nerve cells

Endocrine signaling

cell targets a distant cell through the bloodstream

Example: signaling between endocrine cells and their target cells

Autocrine signaling

cell targets itself

Example: pain sensation and inflammatory responses

Direct signaling across gap junctions

connections between plasma membranes allow intracellular mediators to diffuse between 2 cells

Internal receptors

found in cytoplasm, respond to hydrophobic ligand molecules that travel across the plasma membrane

Cell surface receptors

membrane anchored proteins that bind to external ligand molecules

Ion channel linked receptors

When ligand binds, receptor changes conformation and forms a channel that allows specific ions to pass through

G protein linked receptors

binds a ligand and activates a G-protein, then interacts with an ion channel/enzyme in the membrane (alpha and beta/gamma subunits)

Enzyme linked receptors

have intracellular domains associated with an enzyme

example: receptor tyrosine kinase (RTK)

Signaling molecules that can diffuse through the membrane

small hydrophobic ligands

examples: steroids (cortisol, testosterone, estrogen, etc), gases (CO2, O2)

Signaling molecules that need to bind to a surface receptor

water soluble ligands

Examples: neurotransmitters (acetylcholine, norepinephrine), insulin, adrenaline

Catabolic hormones

stimulate breakdown of molecules and production of energy

examples: cortisol, glucagon, adrenaline/epinephrine

Anabolic hormones

required for the synthesis of molecules

examples: growth hormone, insulin, testosterone, estrogen

Oxidation

releases a small amount of energy (loss of electron)

Reduction

electron and energy are passed to another molecule

Oxidation-reduction reaction/redox reaction

electron is passed between molecules, donor is oxidized and recipient is reduced, always paired, oxidized carrier is more stable

Cellular respiration

Glucose + oxygen = carbon dioxide + water + ATP

Steps of cellular respiration

1. Glycolysis

2. Pyruvate oxidation

3. Krebs cycle

4. Electron transport chain/oxidative phosphorylation

Glycolysis

• Inputs: glucose, ADP, NAD+

• Outputs: 2 pyruvate, ATP, NADH

• Location: cytoplasm/cytosol

• Is oxygen required?: no

Pyruvate oxidation

• Inputs: pyruvate, NAD+

• Outputs: acetyl CoA, NADH, CO2

• Location: mitochondrial matrix

• Is oxygen required?: yes, indirectly (electron acceptor)

Krebs cycle/citric acid cycle

• Inputs: acetyl CoA, NAD+, FAD+, ADP

• Outputs: NADH, FADH2, ATP

• Location: mitochondrial matrix

• Is oxygen required?: yes, indirectly (electron acceptor)

Oxidative phosphorylation/electron transport chain

• Inputs: NADH, FADH2, ADP, O2

• Outputs: lots of ATP (30 ish), H2O, NAD+, FAD+

• Location: mitochondrial membrane

• Is oxygen required?: yes, directly

What happens if there’s no oxygen for cellular respiration?

• During glycolysis, pyruvate is converted into lactate that can be excreted from the cell, goes to the liver

• Cori Cycle: converts lactate into glucose

Gluconeogenesis

synthesis of new glucose molecules from pyruvate, lactate, glycerol, alanine or glutamine

Cell cycle

sequence of events in the life of a cell from the moment it is created until it divides itself

Phases of mitosis

1. Interphase: cells are preparing to divide

2. Mitotic phase: cells are actively dividing (mitosis + cytokinesis)

Interphase

G1: cells are growing larger (synthesizing new biomolecules), copying/making extra organelles, assembling proteins necessary for later steps, longest part of interphase

S: synthesize a copy of the genome, duplicating the centrosome (helps separate DNA in M phase)

G2: more growth, more proteins, final preparations for M phase

Stages of mitotic phase

1. prophase

2. metaphase

3. anaphase

4. telophase

5. cytokinesis

Prophase (mitosis)

chromosomes condense, spindle fibers emerge from centrosomes, nuclear envelope breaks down, centrosomes move toward opposite poles

Metaphase (mitosis)

chromosomes are lined up at the metaphase plate, each sister chromatid is attached to a spindle fiber

Anaphase (mitosis)

sister chromatids are separated and pulled towards opposite poles, cell elongates

Telophase (mitosis)

chromosomes arrive at opposite poles and begin to decondense, nuclear envelope surrounds each set of chromosomes

Cytokinesis (mitosis)

cleavage furrow separates the two daughter cells

How is the cell cycle controlled?

Checkpoints in G1, G2, and M phases can stop cell cycle progression

Cell cycle checkpoints

• G1 checkpoint (main checkpoint): Cell size, Nutrients, proteins/growth factors ready, DNA damage

• G2 checkpoint: DNA damage, Is DNA replication complete

• M checkpoint (spindle checkpoint): Are chromosomes properly attached, Are they aligned correctly

Phases of meiosis

Interphase I

Meiosis I

Interphase II

Meiosis II

Prophase I

chromosomes condense, nuclear envelope breaks down, crossing over occurs between non sister chromatids (formed tetrads)

Prometaphase I

chromosomes continue to condense, spindle fibers attach to kinetochores

Metaphase I

homologous chromosomes randomly assemble at the metaphase plate

Anaphase I

sister chromatids are pulled to opposite poles by spindle fibers

Telophase I/Cytokinesis

separated chromatids arrive at opposite poles, begin to decondense, nuclear envelope forms, cell is divided into two haploid cells

Prophase II

chromatids condense, nuclear envelope fragments

Prometaphase II

nuclear envelope disappears, spindle fibers attach to kinetochores

Metaphase II

sister chromatids line up at metaphase plate

Anaphase II

sister chromatids are pulled apart by spindle fibers

Telophase II/Cytokinesis

chromosomes arrive at opposite poles and decondense, nuclear envelope forms, divides two cells into four haploid cells

4 types of tissues

nervous tissue, muscle tissue, epithelial tissue, connective tissue

Nervous tissue

excitable, generates signals in the form of nerve impulses

Muscle tissue

excitable, responds to stimulation and contracts to provide movement

Epithelial tissue

sheets of cells that cover exterior surfaces of the body, lines internal cavities and passageways, forms certain glands

Connective tissue

Binds cells and organs together; protects, supports, integrates different body parts

Tissue differentiation

Starts after fertilization, totipotent cells give rise to 3 major germ layers (ectoderm, mesoderm, endoderm)

Ectoderm

Hair, nails, skin, nervous system (outer)

Mesoderm

Circulatory system, lungs (epithelial layers), skeletal system, muscular system (middle)

Endoderm

Digestive system, liver, pancreas, lungs (inner)

Tissue membrane

thin layer of cells that covers the outside of body, organs, internal passageways and lining of moveable joint cavities

Connective tissue membrane

formed solely from connective tissue, encapsulates organs and lines moveable joints

Synovial membrane

lines cavity of a freely moveable joint, facilitates free movement

Epithelial membrane

epithelium attached to a layer of connective tissue

Mucous membrane

line body cavities and hollow passageways, produce mucus that protects and lubricates

Serous membrane

lines pleura, pericardium and peritoneum, secretes fluids that lubricate the membrane and reduce friction between organs

Cutaneous membrane

 top layer exposed to external environment, covered with gland cells, protection (skin)

Characteristics of epithelial cells

• Little extracellular space (densely packed)

  • Linked by cell to cell junctions

• Have polarity

  • Apical and basal regions

• Avascular (no blood vessels)

• Secretory, absorptive, and protective functions

Tight junction

separate apical/basal compartments, prevent passage of molecules

Anchoring junction

stabilize tissue

Gap junctions

intracellular passageways that allow signals to pass between neighboring cells

Simple squamous

Location: lungs, heart, blood vessels, lymphatic vessels

Function: allows material to pass through by diffusion and secretes lubricating substance

Stratified squamous

Location: esophagus, mouth, vagina

Function: protect against abrasion

Simple cuboidal

Location: small glands, kidney

Function: secretes and absorbs

Stratified cuboidal

Location: sweat glands, salivary glands, mammary glands

Function: protective tissue

Simple columnar

Location: ciliated = uterine tubes/uterus, non ciliated = digestive tract, bladder

Function: absorbs, secretes mucus and enzymes

Stratified columnar

Location: urethrae, ducts of some glands

Function: secretes and protects

Pseudostratified columnar

Location: bronchi, trachea, upper respiratory tract

Function: secretes mucus, ciliated tissue moves mucus