Chapter 3- Cell Biology Pt 1

Cells

• basic unit of all living things

• components of cells

  • plasma membrane

  • nucleus

  • cytoplasm-

    • contains organelles

Functions of the cell

• Cell metabolism and energy use

• Synthesis of molecules

• Communication

• Reproduction and inheritance

Cell metabolism and energy use

• all chemical reactions in the cell

• often involve energy transfer

• many reactions release heat and play a role in regulating body temperature

Synthesis of molecules

• structural and functional characteristics of cells are determined by the types of molecules they produce

Communication

• use chemical and electrical signals for communication

Reproduction and inheritance

• Reproduction

  • passing genes from one cell to the next during cell division

• Inheritance

  • transmission of traits from one generation to the next, gamete production

Components of the plasma membrane

• Proteins (45-50%)

• Lipids(45-50%)

  • phospholipids

  • cholesterol

• Carbohydrates (4-8%)

  • Glycocalyx

    • glycoproteins and glycolipids on the outer suface of the plasma membrane

Functions of the Plasma Membrane

• Boundary separating the intracellular substances from the extracellular substances

• Encloses and supports the cell contents

• Attaches cells to the extracellular environment or to other cells

• Allows for recognition and communication between cells

• Determines movement of material into and out of the cell

Membrane lipids

• phospholipids

• cholesterol

Phospholipids

form th elipid bilayer due to amphipathic nature

Cholesterol

• Interspersed among the phospholipids

• 1/3 of the total lipids in the plasma membrane

• hydrophilic hydroxyl group allows it to associate with the hydrophilic membrane surface

• determines the fluid nature of the membrane by limiting movements of phospholipids

Fluid Mosaic Model

• membrane is not rigid or static structure

• highly flexible

• changes shape and composition

• dense liquid with proteins suspended in it

• allows for:

  • distribution of molecules in the plasma membrane

  • repair of slight damage

  • membrane fusion

Membrane Proteins

• carry out diverse functions in the plasma membrane

  • marker molecules, attachment proteins, transport proteins, receptor proteins, enzymes

• Integral membrane proteins

  • penetrate deeply into the lipid bilayer

• Peripheral membrane proteins

  • attach to the inner or outer surface of th elipid bilayer

  • can be bound to the integral proteins

Proteins: Marker Molecules

• allow cells to identify other cells or other molecules

• mostly glycoproteins and glycolipids

Attachment Proteins

• integral proteins that allow cells to attach to other cells or extracellular molecules

• often also attach to cytoplasmic molecules

Includes:

• CADHERINS

• INTEGRINS

cadherins

attach cells to other cells

integrins

• attach cells to extracellular molecules

• also attach to cytoplasmic molecules to allow for cellular communication

transport proteins

• integral proteins that allow ions or molecules to move across the plasma membrane

• Characteristics

  • specificity

  • competition

  • saturation

Transport proteins Characteristics- Specificity

bind only a certain type of molecule or ion

Transport proteins Characteristics- Competition

similarly shaped molecules can compete for the same binding site

Result of molecules of similar shape binding

Transport proteins Characteristics- Saturation

rate of movement of the molecule is limited by the number of transport proteins

Classes of Transport Proteins

• Channel Proteins

• Carrier Proteins

• ATP-powered pumps

Channel Proteins

• One or more integral proteins that form a tiny channel through the plasma membrane

• Hydrophobic regions face outward, hydrophilic portion face inward to determine ions that can pass through

• Includes:

  • Leak ion channel

  • Gated ion channel

leak ion channels

always open, responsible for membrane permeability at rest

gated ion channels

open and close depending on conditions of the cell

Carrier Proteins

• Transporters

• Integral proteins that move ions or molecules from one side of the membrane to the other

• Types:

  • Uniporter

  • Symporter

  • Antiporter

Uniporter

moves one ion or molecule

Symporter

moves two different ions or molecules in the same direction

Antiporter

moves two different ions or molecules in opposite directions

ATP-Powered Pumps

require ATP to move specific ions or molecules

Receptor Proteins

• Membrane proteins or glycoproteins that have a receptor site

• Used for intercellular communication

Receptor in receptor proteins can be coupled to

• channel proteins

• G protein complexes

Enzymes

• Catalyze chemical reactions on either side of the plasma membrane

• Can be always active or activated by membrane bound receptors of G protein complexes

Plasma Membrane

• selective permeable

• cell volume must remain constant

• must maintain the differences between intracellular and extracellular material

selective permeable

allows certain substances to pass through

Intracellular

enzymes, other proteins, glycogen, K⁺

Extracellular

Na⁺, Ca²⁺, Cl^-

simple diffusion

• net movement of particles from a place of high concentration to an area of low concentration, down a concentration gradient

• how oxygen and steroid hormones enter cells and carbon dioxide leaves

• DOES NOT USE ENERGY

• nonpolar and hydrophobic substances diffuse through lipid regions of membranes

• hydrophilic substances diffuse through protein channels in the membrane

osmosis

net movement of water through a selectively permeable membrane from area or relatively low concentration of solutes to the area of relatively high solute concentration

tonicity

• ability of a solution to affect intracellular pressure and volume

• determined by concentration of solutes that cannot pass through the plasma membrane

• isotonic

• hypertonic

• hypotonic

isotonic

have the same tonicity, cells gain and lose water at the same rate

hypertonicity

ECF has a higher concentration than ICF, water leaves the cell

hypotonic

ECF has a lower concentration than ICF, water enters the cell

facilitated diffusion

• type of carrier-mediated. transport

  • use carrier proteins in the plasma membrane

• moves molecules that could not pass through the plasma membrane

  • glucose

• solute moves down its concentration gradient

• does not require ATP (energy)

active transport

• type of carrier-mediated transport

• moves molecules up its concentration gradient

• requires ATP (energy)

• sodium-potassium (Na⁺-K⁺) pump

secondary active transport

• involves active transport of an ion out of the cell

• then its movement down the concentration gradient provides the energy necessary to move a different ion/molecule into the cell

vesicular transport

• moves larger particles or droplets of fluid through the membrane

• requires ATP

• Endocytosis

• Exocytosis

Endocytosis

moves matter into the cell

• Phagocytosis

• Pinocytosis

• Receptor-mediated endocytosis

Exocytosis

moves matter out of the cell

transcytosis

substances like large molecules, fluid, and even pathogens are transported across a cell, from one side to the other

cytoplasm

• cellular material outside the nucleus and inside the plasma membrane

• about half cytosol and half organelles

• cytosol

cytosol

• fluid portion of the cytoplasm

• viscous solution containing dissolved ions and molecules with suspended molecules (enzymes, cytoskeleton, cytoplasmic inclusions)

cytoskeleton

• support the cell

• holds the nucleus and organelles in place

• help change the cell shape

• movement of cell organelles

• consists of:

  • microtubules

  • microfilaments (actin filaments)

  • intermediate filaments

cytoplasmic inclusions

• aggregates of chemicals

• produced in the cell or taken in by the cell

• includes:

  • lipid droplets

  • glycogen granules

organelles

• “little organs”

• structures where individual functions of the cell take place

nucleus

• largest organelle

• most cells have only one nucleus

  • mature red blood cells have none, skeletal muscle cells can have dozens of nuclei

• nuclear envelope

• nuclear pores

• nucleoli

nuclear envelope

two layer-membrane surrounding the nucleus

nuclear pores

openings in the nuclear envelope

nucleoli

one or more per nucleus, structure where ribosomes are built

nucleus

chromosomes

• thread like bodies of DNA and protein found in the nucleus

  • 46 chromosomes in most human cells

nucleosomes

structural unit of chromosomes made of DNA wrapped around histones

chromatin

very fine filament broadly dispersed throughout the nucleus of non-dividing cells

ribosomes

• small granules made of protein and ribonucleic acid (RNA)

• produced in the nucleus

• “read” genetic code from the nucleus and build proteins from amino acids

• can be found attached to the nuclear envelope or rough ER or free in cytoplasm

Endoplasmic Reticulum

• membrane bound system of interconnected channels (cisternae)

Rough endoplasmic reticulum

• flat parallel cisternae covered with ribosomes

• continuous with the outer membrane of the nuclear envelope

• functions:

  • produces phospholipids and proteins of the plasma membrane

  • produces secreted proteins

  • produces secreted proteins

  • produces proteins stored in lysosomes

Smooth endoplasmic reticulum

• tubular shaped cisternae with more branching

• lacks ribosomes

• continuous with the rough ER

• functions:

  • synthesizes steroids and other lipids

  • detoxifies alcohol and other drugs

  • manufactures the cells internal and surface membranes

Golgi Complex

• cluster/stack of cisternae

• synthesize carbohydrates and finalize processing of proteins and glycoproteins

• pinches off Golgi Vesicles

  • some are lysosomes

  • some incorporate into the plasma membrane

  • some become secretory vesicles