chapter 3: the cellular level of organization. figure 3–1 the cell performs all life functions
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Chapter 3: The Cellular Level of Organization
Figure 3–1
The Cell
• Performs all life functions
Sex Cells
• Sex cells (germ cells):– reproductive cells – male sperm– female oocytes (eggs)
Somatic Cells
• Somatic cells (soma = body):– all body cells except sex cells
Organelle Functions
Table 3–1 (1 of 2)
Organelle Functions
Table 3–1 (2 of 2)
Functions of Cell Membrane (1 of 2)
• Physical isolation• Monitors & Regulates exchange
with environment:– extracellular fluid composition– chemical signals– ions and nutrients enter– waste and cellular products released
• Structural support: – anchors cells and tissues
Structures and functions of the
cell membrane
The Cell Membrane
• Contains lipids, carbohydrates, and functional proteins
• Double layer of phospholipid molecules:– hydrophilic heads—toward watery
environment, both sides– hydrophobic fatty-acid tails—inside
membrane – barrier to ions and water soluble
compounds
6 Functions of Membrane Proteins (1 of 2)
1. Anchoring proteins (stabilizers):– attach to inside or outside structures
2. Recognition proteins (identifiers): – label cells normal or abnormal
3. Enzymes: – catalyze reactions
6 Functions of Membrane Proteins (2 of 2)
4. Receptor proteins:– bind and respond to ligands (ions,
hormones)
5. Carrier proteins: – transport specific solutes through
membrane
6. Channels: – regulate water flow and solutes through
membrane
Membrane Carbohydrates
• Proteoglycans, glycoproteins, and glycolipids:– extend outside cell membrane– form sticky “sugar coat” (glycocalyx)
Functions of Membrane Carbohydrates
• Lubrication and protection• Anchoring and locomotion• Specificity in binding (receptors)• Recognition (immune response)
Cytoplasm
• All materials inside the cell and outside the nucleus: – cytosol (fluid):
• dissolved materials:– nutrients, ions, proteins, and waste products
– organelles: • structures with specific functions
What are cell organelles and their functions?
Types of Organelles
• Nonmembranous organelles: – no membrane– direct contact with cytosol
• Membranous organelles: – covered with plasma membrane– isolated from cytosol
Nonmembranous Organelles
• 6 types of nonmembranous organelles: – cytoskeleton – microvilli – centrioles – cilia – ribosomes – proteasomes
Figure 3–3a
The Cytoskeleton
• Structural proteins for shape and strength
Microfilaments
• Thin filaments composed of the protein actin: – provide additional mechanical
strength – interact with proteins for consistency– Pairs with thick filaments of myosin
for muscle movement
Intermediate Filaments
• Mid-sized between microfilaments and thick filaments:– durable (collagen)– strengthen cell and maintain shape– stabilize organelles– stabilize cell position
Microtubules
• Large, hollow tubes of tubulin protein:– attach to centrosome– strengthen cell and anchor organelles– change cell shape– move vesicles within cell (kinesin and
dynein)– form spindle apparatus
Figure 3–3b
Microvilli
• Increase surface area for absorption
• Attach to cytoskeleton
Centrioles in the Centrosome
• Centrioles form spindle apparatus during cell division
• Centrosome: cytoplasm surrounding centriole
Figure 3–4a
Cilia Power
• Cilia move fluids across the cell surface
Figure 3–4b,c
Ribosomes
• Build polypeptides in protein synthesis
• Two types: – free ribosomes in cytoplasm:
• proteins for cell
– fixed ribosomes attached to ER:• proteins for secretion
Proteasomes
• Contain enzymes (proteases)• Disassemble damaged proteins for
recycling
Membranous Organelles
• 5 types of membranous organelles:– endoplasmic reticulum (ER)– Golgi apparatus– lysosomes– peroxisomes– mitochondria
Endoplasmic Reticulum (ER)
Figure 3–5a
Endoplasmic Reticulum (ER)
• endo = within, plasm = cytoplasm, reticulum = network
• Cisternae are storage chambers within membranes
Functions of ER
• Synthesis of proteins, carbohydrates, and lipids
• Storage of synthesized molecules and materials
• Transport of materials within the ER
• Detoxification of drugs or toxins
Smooth Endoplasmic Reticulum (SER)
• No ribosomes attached• Synthesizes lipids and carbohydrates:
– phospholipids and cholesterol (membranes)
– steroid hormones (reproductive system)– glycerides (storage in liver and fat cells)– glycogen (storage in muscles)
Rough Endoplasmic Reticulum (RER)
• Surface covered with ribosomes:– active in protein and glycoprotein
synthesis– folds polypeptides protein structures– encloses products in transport
vesicles
Golgi Apparatus
Figure 3–6a
Golgi Apparatus
• Vesicles enter forming face and exit maturing face
Functions of the Golgi ApparatusPLAYPLAY
Vesicles of the Golgi Apparatus
• Secretory vesicles:– modify and package products for
exocytosis
• Membrane renewal vesicles:– add or remove membrane
components
• Lysosomes:– carry enzymes to cytosol
Transport Vesicles
Figure 3–7a
• Carry materials to and from Golgi apparatus
Figure 3–7b
Exocytosis
• Ejects secretory products and wastes
Lysosomes
Figure 3–8
• Powerful enzyme-containing vesicles:– lyso = dissolve, soma = body
Lysosome Structures
• Primary lysosome: – formed by Golgi and inactive
enzymes
• Secondary lysosome: – lysosome fused with damaged
organelle– digestive enzymes activated– toxic chemicals isolated
Lysosome Functions
• Clean up inside cells:– break down large molecules– attack bacteria– recycle damaged organelles– ejects wastes by exocytosis
Autolysis
• Self-destruction of damaged cells:– auto = self, lysis = break– lysosome membranes break down– digestive enzymes released– cell decomposes– cellular materials recycle
Peroxisomes
• Are enzyme-containing vesicles:– break down fatty acids, organic
compounds
– produce hydrogen peroxide (H2O2)
– replicate by division
Membrane Flow
• A continuous exchange of membrane parts by vesicles:– all membranous organelles (except
mitochondria)– allows adaptation and change
KEY CONCEPT
• Cells: basic structural and functional units of life– respond to their environment– maintain homeostasis at the cellular
level– modify structure and function over
time
Mitochondrion Structure
Figure 3–9a
Mitochondrion Structure
• Have smooth outer membrane and folded inner membrane (cristae)
• Matrix: – fluid around cristae
Mitochondrial Function
• Mitochondrion takes chemical energy from food (glucose):– produces energy molecule ATP
Figure 3–9b
Aerobic Cellular Respiration
• Aerobic metabolism (cellular respiration):– mitochondria use oxygen to break
down food and produce ATP
The Reactions
glucose + oxygen + ADP carbon dioxide + water + ATP
• Glycolysis: – glucose to pyruvic acid (in cytosol)
• Tricarboxylic acid cycle (TCA cycle):– pyruvic acid to CO2 (in matrix)
KEY CONCEPT
• Mitochondria provide cells with energy for life:– require oxygen and organic
substrates– generate carbon dioxide and ATP
How does the nucleus control the cell?
Figure 3–10a
The Nucleus
• Is the cell’s control center
Structure of the Nucleus
• Nucleus:– largest organelle
• Nuclear envelope:– double membrane around the nucleus
• Perinuclear space:– between 2 layers of nuclear envelope
• Nuclear pores:– communication passages
Within the Nucleus
• DNA:– all information to build and run
organisms
• Nucleoplasm:– fluid containing ions, enzymes,
nucleotides, and some RNA
• Nuclear matrix:– support filaments
Nucleoli in Nucleus
• Are related to protein production• Are made of RNA, enzymes, and
histones• Synthesize rRNA and ribosomal
subunits
Organization of DNA
• Nucleosomes:– DNA coiled around histones
• Chromatin:– loosely coiled DNA (cells not dividing)
• Chromosomes:– tightly coiled DNA (cells dividing)
What is genetic code?
DNA and Genes
• DNA:– instructions for every protein in the
body
• Gene:– DNA instructions for 1 protein
Genetic Code
• The chemical language of DNA instructions:– sequence of bases (A, T, C, G)– triplet code:
• 3 bases = 1 amino acid
KEY CONCEPT
• The nucleus contains chromosomes
• Chromosomes contain DNA• DNA stores genetic instructions for
proteins• Proteins determine cell structure
and function
How do DNA instructions become proteins?
Protein Synthesis
• Transcription:– copies instructions from DNA to
mRNA (in nucleus)
• Translation:– ribosome reads code from mRNA (in
cytoplasm)– assembles amino acids into
polypeptide chain
Protein Synthesis
• Processing:– by RER and Golgi apparatus produces
protein
mRNA Transcription
• A gene is transcribed to mRNA in 3 steps:– gene activation– DNA to mRNA– RNA processing
Step 1: Gene Activation
• Uncoils DNA, removes histones• Start (promoter) and stop codes on
DNA mark location of gene:– coding strand is code for protein– template strand used by RNA
polymerase molecule
Step 2: DNA to mRNA
• Enzyme RNA polymerase transcribes DNA:– binds to promoter (start) sequence– reads DNA code for gene– binds nucleotides to form messenger
RNA (mRNA)– mRNA duplicates DNA coding strand,
uracil replaces thymine
Step 3: RNA Processing
• At stop signal, mRNA detaches from DNA molecule:– code is edited (RNA processing)– unnecessary codes (introns) removed– good codes (exons) spliced together– triplet of 3 nucleotides (codon)
represents one amino acid
Codons
Table 3–2
Translation (1 of 6)
• mRNA moves: – from the nucleus– through a nuclear
pore
Figure 3–13
Translation (2 of 6)
• mRNA moves:– to a ribosome in
cytoplasm– surrounded by amino
acids
Figure 3–13 (Step 1)
Translation (3 of 6)
• mRNA binds to ribosomal subunits
• tRNA delivers amino acids to mRNA
Figure 3–13 (Step 2)
Translation (4 of 6)
• tRNA anticodon binds to mRNA codon
• 1 mRNA codon translates to 1 amino acid
Figure 3–13 (Step 3)
Figure 3–13 (Step 4)
Translation (5 of 6)
• Enzymes join amino acids with peptide bonds
• Polypeptide chain has specific sequence of amino acids
Protein Synthesis: Sequence of Amino Acids in the Newly Synthesized Polypeptide
PLAYPLAY
Figure 3–13 (Step 5)
Translation (6 of 6)
• At stop codon, components separate
KEY CONCEPT
• Genes: – are functional units of DNA – contain instructions for 1 or more
proteins
• Protein synthesis requires:– several enzymes– ribosomes– 3 types of RNA
KEY CONCEPT
• Mutation is a change in the nucleotide sequence of a gene:– can change gene function
• Causes:– exposure to chemicals– exposure to radiation– mistakes during DNA replication
Overcoming the Cell Barrier
• The cell membrane is semipermeable: – nutrients must get in– products and wastes must get out
Permeability
• Permeability determines what moves in and out of a cell:
• A membrane that: – lets nothing in or out is impermeable– lets anything pass is freely permeable– restricts movement is selectively
permeable
Selective Permeability
• Cell membrane is selectively permeable:– allows some materials to move freely– restricts other materials
Membrane Transport: Fat- and Water-Soluble MoleculesPLAYPLAY
Restricted Materials
• Selective permeability restricts materials based on:– size– electrical charge– molecular shape– lipid solubility
Transport
• Transport through a cell membrane can be:– active (requiring energy and ATP)– passive (no energy required)
3 Categories of Transport
• Diffusion (passive)• Carrier-mediated transport
(passive or active)• Vesicular transport (active)
Solutions
• All molecules are constantly in motion
• Molecules in solution move randomly
• Random motion causes mixing
Concentration Gradient
• Concentration is the amount of solute in a solvent
• Concentration gradient: – more solute in 1 part of a solvent
than another
Function of Concentration Gradient
• Diffusion: – molecules mix randomly – solute spreads through solvent – eliminates concentration gradient
Diffusion
• Solutes move down a concentration gradient
Factors Affecting Diffusion Rates
• Distance the particle has to move• Molecule size:
– smaller is faster
• Temperature: – more heat, faster motion
Factors Affecting Diffusion Rates
• Gradient size: – the difference between high and low
concentration
• Electrical forces: – opposites attract, like charges repel
Diffusion and the Cell Membrane
Figure 3–15
• Diffusion can be simple or channel-mediated
Simple Diffusion
• Materials which diffuse through cell membrane:– lipid-soluble compounds (alcohols,
fatty acids, and steroids)– dissolved gases (oxygen and carbon
dioxide)
Channel-Mediated Diffusion
• Materials which pass through transmembrane proteins (channels):– are water soluble compounds– are ions
Factors in Channel-Mediated Diffusion
• Passage depends on:– size– charge– interaction with the channel
Osmosis
Figure 3–16
• Osmosis is the diffusion of water across the cell membrane
How Osmosis Works
• More solute molecules, lower concentration of water molecules
• Membrane must be freely permeable to water, selectively permeable to solutes
Osmosis Water Movement
• Water molecules diffuse across membrane toward solution with more solutes
• Volume increases on the side with more solutes
Osmotic Pressure
• Is the force of a concentration gradient of water
• Equals the force (hydrostatic pressure) needed to block osmosis
Tonicity
• The osmotic effect of a solute on a cell: – 2 fluids may have equal
osmolarity, but different tonicity
Figure 3–17a
Isotonic Solutions
• A solution that does not cause osmotic flow of water in or out of a cell
• iso = same, tonos = tension
Hypotonic Solutions
• hypo = below• Has less solutes• Loses water through osmosis
Cells and Hypotonic Solutions
• A cell in a hypotonic solution:– gains water– ruptures (hemolysis of
red blood cells)
Figure 3–17b
Hypertonic Solutions
• hyper = above • Has more solutes• Gains water by osmosis
Cells and Hypertonic Solutions
• A cell in a hypertonic solution:– loses water– shrinks (crenation of red
blood cells)
Figure 3–17c
KEY CONCEPT (1 of 2)
• Concentration gradients tend to even out
• In the absence of membrane, diffusion eliminates concentration gradients
KEY CONCEPT (2 of 2)
• When different solute concentrations exist on either side of a selectively permeable membrane, osmosis moves water through the membrane to equalize the concentration gradients
Special transport mechanisms
Special Transport Mechanisms
• Carrier-mediated transport of ions and organic substrates:– facilitated diffusion – active transport
Characteristics of Carrier-Mediated Transport
• Specificity: – 1 transport protein, 1 set of
substrates
• Saturation limits: – rate depends on transport proteins,
not substrate
• Regulation: – cofactors such as hormones
Special Transport Mechanisms
• Cotransport– 2 substances move in the same
direction at the same time
• Countertransport– 1 substance moves in while another
moves out
Facilitated Diffusion
• Passive• Carrier mediated
Figure 3–18
How Facilitated Diffusion Works
• Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids):– molecule binds to receptor site on
carrier protein– protein changes shape, molecules pass
through– receptor site is specific to certain
molecules
Active Transport
• Active transport proteins:– move substrates against
concentration gradient– require energy, such as ATP – ion pumps move ions (Na+, K+, Ca+,
Mg2+) – exchange pump countertransports 2
ions at the same time
Sodium-Potassium Exchange Pump
Figure 3–19
Receptor-Mediated Endocytosis
• Receptors (glycoproteins) bind target molecules (ligands)
• Coated vesicle (endosome) carries ligands and receptors into the cell
Figure 3–22a
Pinocytosis
• Pinocytosis (cell drinking) • Endosomes “drink” extracellular
fluid
Phagocytosis
• Phagocytosis (cell eating)– pseudopodia (psuedo =
false, podia = feet) – engulf large objects in
phagosomes
Figure 3–22b
Figure 3–7b
Exocytosis
• Is the reverse of endocytosis
Summary
Table 3–3
• The 7 methods of transport
What is transmembrane potential?
Electrical Charge
• Inside cell membrane is slightly negative, outside is slightly positive
• Unequal charge across the cell membrane is transmembrane potential
• Resting potential ranges from —10 mV to —100 mV, depending on cell type
Cell Life Cycle
Figure 3–3
Cell Life Cycle
• Most of a cell’s life is spent in a nondividing state (interphase)
3 Stages of Cell Division
• Body (somatic) cells divide in 3 stages:– DNA replication duplicates genetic
material exactly– Mitosis divides genetic material
equally – Cytokinesis divides cytoplasm and
organelles into 2 daughter cells
Interphase
• The nondividing period: – G-zero phase—specialized cell
functions only – G1 phase—cell growth, organelle
duplication, protein synthesis – S phase—DNA replication and histone
synthesis– G2 phase—finishes protein synthesis
and centriole replication
DNA Replication
Figure 3–24
• DNA strands unwind • DNA polymerase attaches
complementary nucleotides
Mitosis
• Mitosis divides duplicated DNA into 2 sets of chromosomes:– DNA coils tightly into chromatids– chromatids connect at a centromere– protein complex around centromere is
kinetochore
Features of Prophase
• Nucleoli disappear • Centriole pairs move to
cell poles• Microtubules extend
between centriole pairs• Nuclear envelope disappears• Spindle fibers attach to
kinetochore
Features of Metaphase
• Chromosomes align in a central plane (metaphase plate)
Features of Anaphase
• Microtubules pull chromosomes apart
• Daughter chromosomes groups near centrioles
Features of Telophase
• Nuclear membranes reform
• Chromosomes uncoil• Nucleoli reappear• Cell has 2 complete
nuclei
KEY CONCEPT
• Mitosis duplicates chromosomes in the nucleus for cell division
Features of Cytokinesis
• Division of the cytoplasm
• Cleavage furrow around metaphase plate
• Membrane closes, producing daughter cells
Long Life, Short Life
• Muscle cells, neurons rarely divide• Exposed cells (skin and digestive
tract) live only days or hours• Normally, cell division balances cell
loss
Factors Changing Cell Division
• Increases cell division:– internal factors (MPF) – extracellular chemical factors (growth
factors)
• Decreases cell division:– repressor genes (faulty repressors cause
cancers)– worn out telomeres (terminal DNA
segments)
Cell Differentiation
• Cells specialize or differentiate:– to form tissues (liver cells, fat cells,
and neurons) – by turning off all genes not needed by
that cell
KEY CONCEPT
• All body cells, except sex cells, contain the same 46 chromosomes
• Differentiation depends on which genes are active and which are inactive
SUMMARY (1 of 4)
• Structures and functions of human cells
• Structures and functions of membranous and nonmembranous organelles
SUMMARY (2 of 4)
• ATP, mitochondria, and the process of aerobic cellular respiration
• Structures and functions of the nucleus:– control functions of nucleic acids– structures and replication of DNA– DNA and RNA in protein synthesis
SUMMARY (3 of 4)
• Structures and chemical activities of the cell membrane:– diffusion and osmosis – active transport proteins– vesicles in endocytosis and exocytosis– electrical properties of plasma
membrane
SUMMARY (4 of 4)
• Stages and processes of cell division:– DNA replication– mitosis– cytokinesis
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