Chapter 3

cell

cell

is the basic structural and functional unit of life

Plasma membrane

forms the outer boundary of the cell

organelles

each performs specific functions

Nucleus

contains the cell’s genetic material and directs cell activities

Cytoplasm

: the material between the plasma membrane and nucleus

Lipid bilayer

- double layer of lipids with imbedded, dispersed proteins

Bilayer

- consists mainly of phospholipids and cholesterol (20%)

Phospholipids

have hydrophobic (nonpolar tails) and hydrophilic (polar heads) bipoles

diffusion, osmosis, mediated transport , vesicular transport

Ions and molecules move across plasma membranes by:

Diffusion

The movement of a solute from an area of higher concentration to an area of lower concentration within a solvent

Solution

: any mixture of liquids, gases, or solids in which the substances are uniformly distributed with no clear boundary between the substances

Solute

: dissolves in a solvent to form a solution

Concentration gradient

: the concentration difference between two points divided by the distance between those two points

Osmosis

The diffusion of a solvent (water) across a selectively permeable membrane via diffusion.

Osmotic pressure

the force required to prevent the movement of water across a selectively permeable membrane

Isosmotic solutions

have the same concentration of solute particles as a reference solution

Hyperosmotic solutions

have a greater concentration of solute particles than a reference solution

Hypoosmotic solutions

have a lesser concentration of solute particles than a reference solution

Channel proteins

form membrane channels (ion channels)

Carrier proteins

bind to ions or molecules and transport them

Uniport (facilitated diffusion)

moves an ion or molecule down its concentration gradient

Symport

moves two or more ions or molecules in the same direction

Antiport

moves two or more ions or molecules in opposite directions

ATP-powered pumps

move ions or molecules against their concentration gradient using the energy from ATP

Secondary active transport

uses the energy of one substance moving down its concentration gradient to move another substance across the plasma membrane

Vesicular Transport

Transport of large particles and macromolecules across plasma membranes

Endocytosis

the movement of materials into cells by the formation of a vesicle

Phagocytosis

: the movement of solid material into cells

o Pinocytosis

: the uptake of small droplets of liquids and the materials in them

Receptor-mediated endocytosis

involves plasma membrane receptors attaching to molecules that are then taken into the cell

Exocytosis

the secretion of materials from cells by vesicle formation

Half cytosol

Consists of a fluid part (the site of chemical reactions), the cytoskeleton, and cytoplasmic inclusions

Cytoskeleton

supports the cell and enables cell movements

Microtubules

– provide support, aid in cell division, and are components of organelles

Actin filaments

– support the plasma membrane and define the shape of the cell

Intermediate filaments

– provide mechanical support to the cell

Cytoplasmic Inclusions -

are aggregates of chemicals either produced by the cell or taken in by the cell (lipids, glycogen, hemoglobin, melanin)

Cytoplasmic Organelles

Specialized subcellular structures with specific functions

Centrioles and ribosomes

Nonmembranous organelles

Mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus

membranous organelles

nucleus

Contains the genetic library with blueprints for nearly all cellular proteins

Nucleoli

dark-staining spherical bodies within the nucleus

Ribosomes:

sites of protein synthesis

Endoplasmic Reticulum (ER) -

Series of membranes forming sacs and tubules that extend from the outer nuclear membrane into the cytoplasm

Rough ER (RER)

Studded with ribosomes , Major site of protein synthesis

Smooth ER (SER)

Does not have ribosomes attached , Major site of lipid and carbohydrate synthesis

Golgi Apparatus

Series of closely packed membranous sacs that collect, package, and distribute proteins and lipids produced by the ER

Secretory vesicles

small, membrane-bound sacs that transport material from the golgi apparatus to the exterior of the cell

Lysosomes

Spherical membranous bags containing digestive enzymes

Peroxisomes

Membranous sacs containing oxidases and catalases

Mitochondria

The major sites of the production of ATP (the major energy source for cells) via aerobic cellular respiration

Centrioles

cylindrical organelles located in the centrosome

Centrosome

a specialized zone of the cytoplasm , the site of microtubule formation

Spindle fibers

Microtubules called —— extend out in all directions from the centrosome

Spindle fibers

are involved in the separation of chromosomes during cell division

Cilia

move substances over the surface of cells

Flagella

are much longer than cilia and propel sperm cells

Microvilli

increase the surface area of cell and aid in absorption and secretion

Transcription

cell makes a copy of the gene necessary to make a particular protein: messenger RNA (mRNA)

Translation

requires both mRNA and transfer RNA (tRNA)

Messenger RNA (mRNA)

carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm

Transfer RNAs (tRNAs)

bound to amino acids base pair with the codons of mRNA at the ribosome to begin the process of protein synthesis

Ribosomal RNA (rRNA)

– a structural component of ribosomes

RNA Polymerase

An enzyme that oversees the synthesis of RNA

Posttranscriptional processing

modifies mRNA before it leaves the nucleus by removing introns (noncoding) and then splicing exons (coding) together with enzymes called spliceosomes

Functional mRNA

consists only of exons

Alternative splicing

produces different combination of exons, allowing one gene to produce more than one type of protein

Translation

Synthesis of proteins in response to the codons of mRNA

Codon

: a set of 3 nucleotides that codes for 1 amino acid during translation

Anticodon

: part of tRNA and consists of three nucleotides and is complementary to a particular codon of mRNA

mitosis

produces new cells for growth and tissue repair

meiosis

produces gametes (sex cells).