Chapter 3: Cells

Cell

The smallest basic structural and functional unit of all living organisms

All human cells have three basic parts

Plasma membrane: semi-permeable outer boundary

Cytoplasm: intracellular fluid containing organelles

Nucleus: DNA containing control center

Three Class of Extracellular Material

Extracellular fluids, cellular secretions, extracellular matrix

Extracellular Fluids

Interstitial fluids bathe within tissues; ex. blood plasma, cerebrospinal fluid protects organs of CNS

Cellular Secretions

Saliva, mucus, and gastric juice

Extracellular Matrix

Complex network of proteins, glycoproteins and sugars that surrounds and supports cells in tissues; outside the cell membrane; substance that acts as glue to hold cells together

Plasma Membrane

Phospholipid bilayer with embedded proteins arranged as a fluid mosaic model; permeability allows it to determine which substances enter or exit the cell

Cholesterol (role in plasma membrane)

Stabilizes lipid bilayer; stiffens the membrane

Glycoproteins and Glycolipids (role in plasma membrane)

Help identify cells

Four Components of Plasma Membrane

Phospholipids- create semipermeable barrier

Proteins- integral and peripheral proteins help move substances in and out of cell

Carbohydrates- help cells recognize each other

Cholesterol- keeps membrane stale and fluid

Integral Membrane Proteins

Crosses into the hydrophobic portion of the lipid bilayer; acts as carriers to move specific ions and molecules across the barrier

Peripheral Membrane Proteins

Loosely associated with membrane, attached to the surface of the membrane; acts as receptors of extracellular signals into the cell (used for cell signaling)

6 Functions of Membrane Proteins

Transport (channels and carriers)

Receptor (transduce signals from one side of membrane to the other)

Enzyme (performs a chemical reaction)

Cell-cell recognition (some glycoproteins serve as identification tags)

Cell-cell joining (linking two cells together)

ECM attachment (helps maintain cell shape and plays role in cell movement)

Tight Junctions

Prevents molecules from passing between cells

Desmosomes

Keeps cells from tearing apart (acts like velcro)

Gap Junctions

Contains channels that allow ions & small molecules to pass between cells

Simple Diffusion

Molecules move directly through the concentration gradient (from high to low), energy isn’t required, ex. hydrophobic molecules like oxygen, carbon dioxide, fat-soluble vitamins

Facilitated Diffusion

The use of a channel or carrier protein to transport molecules passively with the concentration gradient (high to low), ex.glucose, amino acids, ions

Osmosis

Movement of water across a semipermeable membrane, water moves from lower osmolarity to higher osmolarity (moves with gradient)

Passive Transport (three types)

Does not require ATP; three types are simple diffusion, facilitated diffusion, osmosis

Active Transport (two types)

Requires ATP and molecules are moved against their concentration gradients; larger and polar molecules can be moved; requires carrier proteins; two types are active transport and vesicular transport

Osmolarity

The concentration of solute; solvent = water and solute = substances dissolved in water

Tonicity

Ability of the extracellular fluid to change the shape of a cell

Isotonic Solution

Cell volume is stable (ECF = ICF)

Hypertonic Solution

Cell volume shrinks (ECF > ICF)

Hypotonic Solution

Cell volume grows (ECF < ICF)

Sodium-Potassium Pump

Most known example of active transport; moves sodium out of cell and potassium into cell; is vital for maintaining resting membrane potential

Aquaporins

Specialized water channels that speed up osmosis

Endocytosis

Active transport process, transporting external materials into cells

Exocytosis

Active transport process, transporting large molecules/waste out of cells

Pinocytosis

A cell engulfs extracellular fluids and dissolves small solutes

Phagocytosis

A cell uses its plasma membrane to engulf and digest large solid particles

Receptor-mediated Endocytosis

Specific substances using specific receptors on cell membrane

Mitochondria (structure and function)

Surrounded by a double membrane, produces the most ATP

Cytoplasm

All cellular material between the plasma membrane and nucleus; it is composed of cytosol (gel-like portion of cytoplasm), insoluble molecules, organelles (metabolic machinery structures of the cell

Rough Endoplasmic Reticulum

Site of synthesis for secreted proteins and membrane proteins

Smooth Endoplasmic Reticulum

Stores calcium, metabolizes lipids and glucose

Golgi Apparatus

Packages proteins from RER into secretory vesicles

Lysosomes

Acidic vesicles containing digestive enzymes; digests particles and microorganisms taken in my endocytosis; breaks down nonfunctional organelles through a process called autophagy

Nucleus

Site of DNA and RNA synthesis; surrounded by a nuclear envelope spotted with nuclear pores; contains nucleoli (site of ribosome synthesis)

Peroxisomes

Break down toxic substances like hydrogen peroxide and metabolize fatty acids

Chromatin

consists of DNA wrapped around histone proteins, DNA packaging

Nuclear Envelope

Double membrane structure that surrounds and protects the cell nucleus

Nucleolus

Membrane-less structure inside of the nucleus that primarily produces and assembles ribosomes

Cytoskeleton

Supports cell structures, provides machinery for cellular and subcellular movement, includes three filament types (microfilaments, intermediate filaments, microtubules)

Microfilaments

Made of actin protein; form cleavage furrow, responsible for membrane changes needed for endocytosis and exocytosis)

Intermediate Filaments

Attach to desmosomes to help cells resist external forces; maintain the shape of nucleus

Microtubules

Made of tubulin protein; determine cell shape and organelle distributions, form mitotic spindle for cell division, form cilia and flagella for cell movement

Cilia

Extension formed by centrioles that propel substances across a cell surface; tiny hair-like structures found on the surface of cells, in airways or the brain

Flagella

Extensions that propel the cell; spiral structures found on the outside of the cell membrane

Microvilli

Increase surface area of cell membrane to maximize the absorption of nutrients; found on small intestine and surface of specific epithelial cells

Centrosome

Microtubule organizing center, responsible for formation of mitotic spindles for cell division, consisted of centrioles

Interphase (subphases)

G1: growth and metabolism

S (synthesis): DNA replication

G2: preparation for cell division

S-Phase (interphase)

Uncoiling & separation (helicase unwinds DNA); Assembly (DNA polymerase adds nucleotides to each DNA template to form new strands; Restoration (ligase seals the strand)

Semiconservative Replication

Each new chromosome will have 1 strand from the old chromosome and 1 newly-synthesized strand; 1 daughter chromosome will go to each daughter cell with cell division

Cytokinesis

Dividing of cytoplasm into 2 daughter cells

Prophase

Chromatin condenses; sister chromatids are held together by a centromere; mitotic spindle forms; nuclear envelope breaks up

Metaphase

Chromosomes line up to the middle, spindle fibers are attached to centromeres

Anaphase

Centromeres of chromosomes split and get pulled towards the poles of the cell

Telophase

Chromosomes decondense to form chromatin (individual chromosomes are no longer available)

3 Stages of DNA Replication

Initiation, Elongation, Termination

Initiation

Helicase unwinds and unzips the DNA double helix to form a replication fork

Elongation

Primase builds a short RNA primer to give DNA polymerase a starting point, DNA polymerase reads the template strand and adds matching nucleotides

Termination

RNA primers are replaced with DNA nucleotides and ligase seals the DNA strand

Helicase

Unwinds the DNA double helix for replication

DNA Polymerase

Reads template strand and adds nucleotides

Ligase

Seals the strand of DNA during replication

Genetic Code

Set of rules used by living cells to translate information stored in DNA sequences into proteins

Transcription

Creation of mRNA from the strand of DNA, mRNA is processed and exported from the nucleus once created and serves as a template for protein translation

Translation

Strand of mRNA is translated to create a protein, tRNA brings the correct amino acids that will be used to make the protein and rRNA works with proteins to build ribosomes (where proteins are assembled)

tRNA

Acts as an anticodon to match up with the mRNA codon, has an attachment site for its specific amino acid on the other end

rRNA

Acts as an enzyme to catalyze the chemical bonds that link amino acids together into a growing chain

Ribosome

Organelle responsible for translation; translates amino acid chains from mRNA templates

Where Transcription Occurs

Nucleus

Where Translation Occurs

In cytoplasm on ribosomes

Role of DNA in gene expression

Has the blueprint-genetic code that allows for the protein to be built and expressed

G1 Checkpoint

restriction point, gate only opens if cell growth is sufficient

G2 Checkpoint

Gate opens if DNA replication is complete without major errors

Substances that travel through nuclear pores in nuclear envelope

Small water soluble molecules, ions and ATP

Gene

Unit of heredity made up of a specific sequence of DNA