Chapter 3
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Transcript of Chapter 3
Cell TheoryCell Theory Cells are the building blocks of the human
body 4 concepts of the cell theory:
Cells are the building blocks of all plants and animals
Cells are the smallest functioning units of life Cells are produced through the division of
preexisting cells Each cells maintain homeostasis
The Study of Cells and Their The Study of Cells and Their AnatomyAnatomy
Cytology – the study of the structure and function of cells The 2 most common methods used to study cell and tissue
structure are light microscopy and electron microscopy Anatomy:
Extracellular fluid – watery medium surrounding cells In tissues it’s called interstitial fluid
Plasma (Cell) membrane – separates the cell contents (cytoplasm) from extracellular fluid
Nucleus – control center for cellular operations Cytoplasm subdivides into:
Cytosol – liquid in cell Organelles – intracellular structures
Copyright © 2010 Pearson Education, Inc. Figure 3.2
Secretion beingreleased from cellby exocytosis
Peroxisome
Ribosomes
Roughendoplasmicreticulum
Nucleus
Nuclear envelopeChromatin
Golgi apparatus
NucleolusSmooth endoplasmicreticulum
CytosolLysosome
Mitochondrion
CentriolesCentrosomematrix
Cytoskeletalelements• Microtubule• Intermediate filaments
Plasmamembrane
Plasma MembranePlasma Membrane General functions include:
Physical isolation A physical barrier that separates the inside of the cell from
the extracellular fluid Regulation of exchange with the environment
Controls the entry of ions and nutrients, the elimination of wastes, and the release of secretions
Sensitivity to the environment Contains a variety of receptors that enable the cell to
recognize and respond to specific molecules in the environment
Structural support For tissues
Copyright © 2010 Pearson Education, Inc. Figure 3.3
Integralproteins
Extracellular fluid(watery environment)
Cytoplasm(watery environment)
Hydrophilic head ofphospholipid molecule Glycolipid
Cholesterol
Peripheralproteins
Bimolecularlipid layercontainingproteins
Inward-facinglayer ofphospholipids
Outward-facinglayer of phospholipids
Carbohydrate of glycocalyx
Glycoprotein
Filament of cytoskeleton
Hydrophobictail of phospholipid molecule
Plasma MembranePlasma Membrane Membrane Lipids
The phospholipids in a plasma membrane lie in 2 distinct layers: (phospholipid bilayer) Phosphate heads: polar and hydrophilic Fatty acid tails: nonpolar and hydrophobic
The hydrophobic tails won’t associate with water or charged molecules, allowing the plasma membrane to act as a physical barrier Lipid-soluble molecules, oxygen, CO2, etc. are able to cross Ions and water-soluble compounds cannot
Membrane Proteins The most common of these membrane proteins span the width of the
membrane 1 or more times and are known as transmembrane proteins May function as receptors, channels, carriers, enzymes, anchors, and
identifiers Membrane Carbohydrates
Carbs form complex molecules with proteins and lipids on the outer surface of the membrane
Function as cell lubricants and adhesives, receptors for extracellular compounds, and form part of a recognition system from attacking the body’s cells and tissues
Diffusion and FiltrationDiffusion and Filtration The permeability of the plasma membrane is the property that
determines precisely which substances can enter or leave the cytoplasm. If nothing can cross a membrane, it’s impermeable
If any substance can cross without difficulty, it’s freely permeable
Plasma membranes are selectively permeable
Based on size, charge, shape, solubility Movement is either passive or active
Passive – move ions or molecules across the plasma membrane without any energy expenditure by the cell Diffusion
Osmosis Filtration
Active – require that the cell expend energy, usually in the form of ATP
DiffusionDiffusion The net movement of molecules from an area of
relatively high concentration to an area of relatively low concentration The different areas create a concentration gradient Movement happens until the gradient no longer exists
Diffusion Across Plasma Membranes An ion or molecule can independently diffuse across a
plasma membrane by either: Moving across the lipid portion of the membrane Passing through the channel protein in the membrane
Diffusion ability depends on lipid solubility and size
OsmosisOsmosis The diffusion of water across a membrane Because dissolved solute molecules occupy space that would
otherwise be taken up by water molecules, the higher the solute concentration, the lower the water concentration As a result, water molecules tend to flow across a membrane
toward the solution containing the higher solute concentration, because this movement is down the concentration gradient for water molecules
Three characteristics of osmosis that are important to remember: Osmosis is the diffusion of water molecules across a membrane Osmosis occurs across a selectively permeable membrane that is
freely permeable to water but is not freely permeable to solutes In osmosis, water flows across a membrane toward the solution
that has the higher concentration of solutes, because that is where the concentration of water is lower
Osmosis (cont.)Osmosis (cont.) The osmotic pressure of a
solution is an indication of the force of water movement into that solution as a result of solute concentration
Pushing against a fluid generates hydrostatic pressure Can be either isotonic (no
net movement), hypotonic (water flows in and swells the cell and lyse), or hypertonic (water flows out of the cells and causes shriveling called crenation)
FiltrationFiltration In this passive process, hydrostatic pressure forces
water across a membrane If solute molecules are small enough to fit through
membrane pores, they will be carried through with the water
Filtration across specialized blood vessels in the kidneys is an essential step in the production of urine
Carrier-Mediated TransportCarrier-Mediated Transport Requires the presence of specialized membrane proteins It can be passive (no ATP required) or active (ATP
dependent), depending on the substance being transport and the nature of the transport mechanism
In CMT , membrane proteins bind specific ions or organic substrates and carry them across the plasma membrane
Passive = high conc. to low conc. Active = low conc. to high conc.
Countertransport – when one substance is moved into a cell while the other is moved out
Cotransport – 2 substances are moved into or out of a cell at the same time
Carrier-Mediated Transport (cont.)Carrier-Mediated Transport (cont.) Facilitated Diffusion
Used when essential nutrients are insoluble in lipids and too large to fit through membrane channels. Passively transported across the membrane by carrier proteins First, the molecule binds to a receptor site on the carrier protein. Then
the shape of the protein changes, moving the molecule to the inside of the plasma membrane, where it is released into the cytoplasm
Active Transport In this case, the high energy bond in ATP provides the energy needed to
move ions or molecules across the membrane Despite the energy cost, this transport has one great advantage : it isn’t
concentration gradient dependent All cells have ion pumps that actively transport Na+, K +, Ca2+, and Mg2+
across plasma membranes either in or out of the cell. If one kind of ion is moving in and another is moving out it is called an exchange pump Exchange pumps mainly function in maintaining cell homeostasis Sodium-potassium exchange pump
Lipid-insoluble solutes (such as sugars or amino acids)
Carrier-mediated facilitated diffusion via a protein carrier specific for one chemical; binding of substrate causes shape change in transport protein
Vesicular TransportVesicular Transport Involves the movement of materials within small
membranous sacs called vesicles Always an active process 2 major categories:
Endocytosis – the packaging of extracellular materials in a vesicle at the cell surface for import into the cell 3 types: receptor-mediated endocytosis (involves the formation
of small vesicles at the membrane surface to import substances), pinocytosis (“cell drinking”, the formation of small vesicles filled with extracellular fluid), and phagocytosis (“cell eating”, produces vesicles containing solid objects that may be as large as the cell itself)
Exocytosis – the functional reverse of endocytosis. In exocytosis, a vesicle created inside the cell fuses with the plasma membrane and discharges its contents into the extracellular environment Ejected material may be a secretion or waste product
The CytosolThe Cytosol Cytoplasm is a general term for material inside the
cell including the cytosol and the organelles Cytosol is the intracellular fluid , which contains
dissolved nutrients, ions, soluble and insoluble proteins, and waste products
It differs from extracellular fluid in that: Contains a higher concentration of potassium ions and a
lower concentration of sodium ions Has a high concentration of dissolved proteins Usually contains small quantities of carbohydrates and
large reserves of amino acids and lipids
The OrganellesThe Organelles Internal structures that perform specific functions essential
to normal cell structure, maintenance, and metabolism Cytoskeleton – internal protein framework of various threadlike
filaments and hollow tubules that gives the cytoplasm strength and flexibility Microfilaments, intermediate filaments, and microtubules
(anchors major organelles) Microvilli – small, finger shaped projections of the plasma
membrane on the exposed surfaces of many cells. Increase surface area for absorption
Centrioles, Cilia, and Flagella Centrioles – cylindrical structure composed of short
microtubules Cilia – relatively long, slender extensions of the plasma
membrane. Undergo active movements that require ATP Flagella – move a cell through surrounding fluid, rather than
moving the fluid past a stationary cell
The Organelles (cont.)The Organelles (cont.) Ribosomes – manufacture proteins using information provided
by DNA. Can be either free or fixed Proteasomes – remove and recycle damaged or denatured
proteins and for breaking down abnormal proteins The Endoplasmic Reticulum (ER) – a network of intracellular
membranes connected to the membranous nuclear envelope surrounding the nucleus. 4 major functions: snythesis of proteins, carbs and lipids, storage of synthesized molecules/materials, transport of materials, and detoxification Smooth ER and Rough ER: ratio depends on cell function
Golgi Apparatus – consists of a set of 5 or 6 flattened membranous discs. Main functions: modification and packaging of secretions, renewal or modification of the PM, and packaging of special exzymes. Creates lysosomes, secretory vesicles, and membrane renewal vesicles
The Organelles (cont.)The Organelles (cont.) Lysosomes – filled with digestive enzymes. Perform
cleanup and recycling functions within the cell Peroxisomes – smaller than lysosomes and carry a
different group of enzymes. Absorb and break down fatty acids and other organic compounds
Mitochondria – small organelles that provide energy via ATP bonds for the cell. Have a double membrane
Nucleus – control center for cellular operations. Stores all the information needed to control the synthesis of more than 100,000 different proteins. Determines both the structure of the cell and the and the functions it can perform by controlling which proteins synthesized, under what circumstances, and in what amounts
Transcription and TranslationTranscription and Translation Transcription – the production of mRNA from a single strand of DNA
Takes place in the nucleus Steps:
RNA polymerase binds to the promoter of a gene Promotes the synthesis of an mRNA strand using complementary nucleotides A sequence of 3 nitrogenous bases along the new mRNA strand represents a codon
that corresponds to a triplet on the gene At the DNA “stop” signal the mRNA detaches
Translation – the assembling of a protein by ribosomes, using the information carried by the RNA molecule Takes place in the cytoplasm Steps:
Begins at the “start” codon of mRNA (AUG) with the attachment of the first tRNA carrying an amino acid
The small and large ribosomal subunits join together to enclose the mRNA A second tRNA arrives, carrying a different amino acid, and binds to the next codon Ribosomal enzymes remove AA1 from its tRNA and attach it to AA2 with a peptide
bond This continues until it reaches the “stop” codon, where the strand detaches
Nuclearpores
mRNA
Pre-mRNARNA Processing
Transcription
Translation
DNA
Nuclearenvelope
Ribosome
Polypeptide
1
2
3
4
Leu
Leu
Energized by ATP, the correct aminoacid is attached to each species oftRNA by aminoacyl-tRNA synthetaseenzyme.
Amino acid
tRNA
Aminoacyl-tRNAsynthetase
G A A
tRNA “head”bearinganticodon
Psite A
siteE
site
Ile
Pro
A AU U UC C C
CG G
G
Largeribosomalsubunit
Smallribosomalsubunit
Direction ofribosome advancePortion of mRNA
already translated
Codon15
Codon16
Codon17
Nucleus
mRNA
Released mRNA
Nuclearmembrane
Nuclear pore
RNA polymerase
Templatestrand ofDNA
After mRNA synthesis in thenucleus, mRNA leaves the nucleusand attaches to a ribosome.
Translation begins as incomingaminoacyl-tRNA recognizes thecomplementary codon calling forit at the A site on the ribosome. Ithydrogen-bonds to the codon viaits anticodon.
As the ribosome moves alongthe mRNA, and each codon isread in sequence, a new aminoacid is added to the growingprotein chain and the tRNA inthe A site is translocated to theP site.
Once its amino acid is releasedfrom the P site, tRNA is ratchetedto the E site and then released toreenter the cytoplasmic pool,ready to be recharged with a newamino acid. The polypeptide isreleased when the stop codon isread.
G A A
UU
A
SECOND BASE
UUGUUAUUCUUU
Phe
Leu
CUGCUACUCCUU
Leu
AUAAUCAUU
Ile
GUGGUAGUCGUU
Val
UCGUCAUCCUCU
Ser
CCGCCACCCCCU
Pro
ACGACAACCACU
Thr
GCGGCAGCCGCU
Ala
UACUAU
Tyr
CAGCAACACCAU
His
Gln
AAGAAAAACAAU
Asn
Lys
GAGGAAGACGAU
Asp
Glu
UGCUGU
Cys
Trp
CGGCGACGCCGU
Arg
AGGAGAAGCAGU
Ser
Arg
GGGGGAGGCGGU
Gly
UAA Stop UGA Stop
AUG Met orStart
UAG Stop UGG
U C A G
GACU
GACU
GACU
GACU
U
C
A
G
Cell Life CycleCell Life Cycle The duplication of a cell’s genetic material is called DNA replication, and
nuclear division is called mitosis (only in somatic cells) Sex cells = meiosis
Stages: Interphase – where cells spend most of their lives, an interval of time in which they
perform normal functions Four subphases:
G1 (gap 1)—vigorous growth and metabolism G0—gap phase in cells that permanently cease dividing S (synthetic)—DNA replication G2 (gap 2)—preparation for division
Stage 1 – prophase – begins when the chromosomes become visible, each with two chromatids joined at a centromere. Centrosomes separate and migrate toward opposite poles. Mitotic spindles and asters form
Stage 2 – metaphase – chromatids move to a narrow central plate called the metaphase plate
Stage 3 – anaphase – shortest phase, chromatids separate and begin moving to the poles of the cell
Stage 4 – telophase – the cell prepares to return to interphase. Nuclear membrane forms and chromosomes uncoil
Cytokinesis – the cytoplasmic division that forms 2 daughter cells. Marks the end of cell division
G1
Growth
SGrowth and DNA
synthesis G2
Growth and finalpreparations for
divisionM
G2 checkpoint
G1 checkpoint(restriction point)