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Chapter 3: The Cellular Level of Organization

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1 Chapter 3: The Cellular Level of Organization

2 The Cell Performs all life functions Figure 3–1

3 Sex Cells Sex cells (germ cells): reproductive cells male sperm
female oocytes (eggs)

4 Somatic Cells Somatic cells (soma = body):
all body cells except sex cells

5 Organelle Functions Table 3–1 (1 of 2)

6 Organelle Functions Table 3–1 (2 of 2)

7 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

8 Structures and functions of the cell membrane

9 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

10 6 Functions of Membrane Proteins (1 of 2)
Anchoring proteins (stabilizers): attach to inside or outside structures Recognition proteins (identifiers): label cells normal or abnormal Enzymes: catalyze reactions

11 6 Functions of Membrane Proteins (2 of 2)
Receptor proteins: bind and respond to ligands (ions, hormones) Carrier proteins: transport specific solutes through membrane Channels: regulate water flow and solutes through membrane

12 Membrane Carbohydrates
Proteoglycans, glycoproteins, and glycolipids: extend outside cell membrane form sticky “sugar coat” (glycocalyx)

13 Functions of Membrane Carbohydrates
Lubrication and protection Anchoring and locomotion Specificity in binding (receptors) Recognition (immune response)

14 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

15 What are cell organelles and their functions?

16 Types of Organelles Nonmembranous organelles: Membranous organelles:
no membrane direct contact with cytosol Membranous organelles: covered with plasma membrane isolated from cytosol

17 Nonmembranous Organelles
6 types of nonmembranous organelles: cytoskeleton microvilli centrioles cilia ribosomes proteasomes

18 The Cytoskeleton Structural proteins for shape and strength
Figure 3–3a

19 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

20 Intermediate Filaments
Mid-sized between microfilaments and thick filaments: durable (collagen) strengthen cell and maintain shape stabilize organelles stabilize cell position

21 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

22 Microvilli Increase surface area for absorption Attach to cytoskeleton
Figure 3–3b

23 Centrioles in the Centrosome
Centrioles form spindle apparatus during cell division Centrosome: cytoplasm surrounding centriole Figure 3–4a

24 Cilia Power Cilia move fluids across the cell surface Figure 3–4b,c

25 Ribosomes Build polypeptides in protein synthesis Two types:
free ribosomes in cytoplasm: proteins for cell fixed ribosomes attached to ER: proteins for secretion

26 Proteasomes Contain enzymes (proteases)
Disassemble damaged proteins for recycling

27 Membranous Organelles
5 types of membranous organelles: endoplasmic reticulum (ER) Golgi apparatus lysosomes peroxisomes mitochondria

28 Endoplasmic Reticulum (ER)
Figure 3–5a

29 Endoplasmic Reticulum (ER)
endo = within, plasm = cytoplasm, reticulum = network Cisternae are storage chambers within membranes

30 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

31 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)

32 Rough Endoplasmic Reticulum (RER)
Surface covered with ribosomes: active in protein and glycoprotein synthesis folds polypeptides protein structures encloses products in transport vesicles

33 Golgi Apparatus Figure 3–6a

34 Golgi Apparatus Vesicles enter forming face and exit maturing face
PLAY Functions of the Golgi Apparatus

35 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

36 Transport Vesicles Carry materials to and from Golgi apparatus
Figure 3–7a

37 Exocytosis Ejects secretory products and wastes Figure 3–7b

38 Lysosomes Powerful enzyme-containing vesicles:
lyso = dissolve, soma = body Figure 3–8

39 Lysosome Structures Primary lysosome: Secondary lysosome:
formed by Golgi and inactive enzymes Secondary lysosome: lysosome fused with damaged organelle digestive enzymes activated toxic chemicals isolated

40 Lysosome Functions Clean up inside cells: break down large molecules
attack bacteria recycle damaged organelles ejects wastes by exocytosis

41 Autolysis Self-destruction of damaged cells:
auto = self, lysis = break lysosome membranes break down digestive enzymes released cell decomposes cellular materials recycle

42 Peroxisomes Are enzyme-containing vesicles:
break down fatty acids, organic compounds produce hydrogen peroxide (H2O2) replicate by division

43 Membrane Flow A continuous exchange of membrane parts by vesicles:
all membranous organelles (except mitochondria) allows adaptation and change

44 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

45 Mitochondrion Structure
Figure 3–9a

46 Mitochondrion Structure
Have smooth outer membrane and folded inner membrane (cristae) Matrix: fluid around cristae

47 Mitochondrial Function
Mitochondrion takes chemical energy from food (glucose): produces energy molecule ATP Figure 3–9b

48 Aerobic Cellular Respiration
Aerobic metabolism (cellular respiration): mitochondria use oxygen to break down food and produce ATP

49 glucose + oxygen + ADP  carbon dioxide + water + 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)

50 KEY CONCEPT Mitochondria provide cells with energy for life:
require oxygen and organic substrates generate carbon dioxide and ATP

51 How does the nucleus control the cell?

52 The Nucleus Is the cell’s control center Figure 3–10a

53 Structure of the Nucleus
largest organelle Nuclear envelope: double membrane around the nucleus Perinuclear space: between 2 layers of nuclear envelope Nuclear pores: communication passages

54 Within the Nucleus DNA: Nucleoplasm: Nuclear matrix:
all information to build and run organisms Nucleoplasm: fluid containing ions, enzymes, nucleotides, and some RNA Nuclear matrix: support filaments

55 Nucleoli in Nucleus Are related to protein production
Are made of RNA, enzymes, and histones Synthesize rRNA and ribosomal subunits

56 Organization of DNA Nucleosomes: Chromatin: Chromosomes:
DNA coiled around histones Chromatin: loosely coiled DNA (cells not dividing) Chromosomes: tightly coiled DNA (cells dividing)

57 What is genetic code?

58 DNA and Genes DNA: Gene: instructions for every protein in the body
DNA instructions for 1 protein

59 Genetic Code The chemical language of DNA instructions:
sequence of bases (A, T, C, G) triplet code: 3 bases = 1 amino acid

60 KEY CONCEPT The nucleus contains chromosomes Chromosomes contain DNA
DNA stores genetic instructions for proteins Proteins determine cell structure and function

61 How do DNA instructions become proteins?

62 Protein Synthesis Transcription: Translation:
copies instructions from DNA to mRNA (in nucleus) Translation: ribosome reads code from mRNA (in cytoplasm) assembles amino acids into polypeptide chain

63 Protein Synthesis Processing:
by RER and Golgi apparatus produces protein

64 mRNA Transcription A gene is transcribed to mRNA in 3 steps:
gene activation DNA to mRNA RNA processing

65 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

66 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

67 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

68 Codons Table 3–2

69 Translation (1 of 6) mRNA moves: from the nucleus
through a nuclear pore Figure 3–13

70 Translation (2 of 6) mRNA moves: to a ribosome in cytoplasm
surrounded by amino acids Figure 3–13 (Step 1)

71 Translation (3 of 6) mRNA binds to ribosomal subunits
tRNA delivers amino acids to mRNA Figure 3–13 (Step 2)

72 Translation (4 of 6) tRNA anticodon binds to mRNA codon
1 mRNA codon translates to 1 amino acid Figure 3–13 (Step 3)

73 Translation (5 of 6) Enzymes join amino acids with peptide bonds
Polypeptide chain has specific sequence of amino acids Figure 3–13 (Step 4)

74 Translation (6 of 6) At stop codon, components separate
Protein Synthesis: Sequence of Amino Acids in the Newly Synthesized Polypeptide PLAY Figure 3–13 (Step 5)

75 KEY CONCEPT Genes: Protein synthesis requires:
are functional units of DNA contain instructions for 1 or more proteins Protein synthesis requires: several enzymes ribosomes 3 types of RNA

76 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

77 Overcoming the Cell Barrier
The cell membrane is semipermeable: nutrients must get in products and wastes must get out

78 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

79 Selective Permeability
Cell membrane is selectively permeable: allows some materials to move freely restricts other materials Membrane Transport: Fat- and Water-Soluble Molecules PLAY

80 Restricted Materials Selective permeability restricts materials based on: size electrical charge molecular shape lipid solubility

81 Transport Transport through a cell membrane can be:
active (requiring energy and ATP) passive (no energy required)

82 3 Categories of Transport
Diffusion (passive) Carrier-mediated transport (passive or active) Vesicular transport (active)

83 Solutions All molecules are constantly in motion
Molecules in solution move randomly Random motion causes mixing

84 Concentration Gradient
Concentration is the amount of solute in a solvent Concentration gradient: more solute in 1 part of a solvent than another

85 Function of Concentration Gradient
Diffusion: molecules mix randomly solute spreads through solvent eliminates concentration gradient

86 Diffusion Solutes move down a concentration gradient

87 Factors Affecting Diffusion Rates
Distance the particle has to move Molecule size: smaller is faster Temperature: more heat, faster motion

88 Factors Affecting Diffusion Rates
Gradient size: the difference between high and low concentration Electrical forces: opposites attract, like charges repel

89 Diffusion and the Cell Membrane
Diffusion can be simple or channel-mediated Figure 3–15

90 Simple Diffusion Materials which diffuse through cell membrane:
lipid-soluble compounds (alcohols, fatty acids, and steroids) dissolved gases (oxygen and carbon dioxide)

91 Channel-Mediated Diffusion
Materials which pass through transmembrane proteins (channels): are water soluble compounds are ions

92 Factors in Channel-Mediated Diffusion
Passage depends on: size charge interaction with the channel

93 Osmosis Osmosis is the diffusion of water across the cell membrane
Figure 3–16

94 How Osmosis Works More solute molecules, lower concentration of water molecules Membrane must be freely permeable to water, selectively permeable to solutes

95 Osmosis Water Movement
Water molecules diffuse across membrane toward solution with more solutes Volume increases on the side with more solutes

96 Osmotic Pressure Is the force of a concentration gradient of water
Equals the force (hydrostatic pressure) needed to block osmosis

97 Tonicity The osmotic effect of a solute on a cell:
2 fluids may have equal osmolarity, but different tonicity Figure 3–17a

98 Isotonic Solutions A solution that does not cause osmotic flow of water in or out of a cell iso = same, tonos = tension

99 Hypotonic Solutions hypo = below Has less solutes
Loses water through osmosis

100 Cells and Hypotonic Solutions
A cell in a hypotonic solution: gains water ruptures (hemolysis of red blood cells) Figure 3–17b

101 Hypertonic Solutions hyper = above Has more solutes
Gains water by osmosis

102 Cells and Hypertonic Solutions
A cell in a hypertonic solution: loses water shrinks (crenation of red blood cells) Figure 3–17c

103 KEY CONCEPT (1 of 2) Concentration gradients tend to even out
In the absence of membrane, diffusion eliminates concentration gradients

104 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

105 Special transport mechanisms

106 Special Transport Mechanisms
Carrier-mediated transport of ions and organic substrates: facilitated diffusion active transport

107 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

108 Special Transport Mechanisms
Cotransport 2 substances move in the same direction at the same time Countertransport 1 substance moves in while another moves out

109 Facilitated Diffusion
Passive Carrier mediated Figure 3–18

110 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

111 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

112 Sodium-Potassium Exchange Pump
Figure 3–19

113 Receptor-Mediated Endocytosis
Receptors (glycoproteins) bind target molecules (ligands) Coated vesicle (endosome) carries ligands and receptors into the cell

114 Pinocytosis Pinocytosis (cell drinking)
Endosomes “drink” extracellular fluid Figure 3–22a

115 Phagocytosis Phagocytosis (cell eating)
pseudopodia (psuedo = false, podia = feet) engulf large objects in phagosomes Figure 3–22b

116 Exocytosis Is the reverse of endocytosis Figure 3–7b

117 Summary The 7 methods of transport Table 3–3

118 What is transmembrane potential?

119 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

120 Cell Life Cycle Figure 3–3

121 Cell Life Cycle Most of a cell’s life is spent in a nondividing state (interphase)

122 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

123 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

124 DNA Replication DNA strands unwind
DNA polymerase attaches complementary nucleotides Figure 3–24

125 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

126 Features of Prophase Nucleoli disappear
Centriole pairs move to cell poles Microtubules extend between centriole pairs Nuclear envelope disappears Spindle fibers attach to kinetochore

127 Features of Metaphase Chromosomes align in a central plane (metaphase plate)

128 Features of Anaphase Microtubules pull chromosomes apart
Daughter chromosomes groups near centrioles

129 Features of Telophase Nuclear membranes reform Chromosomes uncoil
Nucleoli reappear Cell has 2 complete nuclei

130 KEY CONCEPT Mitosis duplicates chromosomes in the nucleus for cell division

131 Features of Cytokinesis
Division of the cytoplasm Cleavage furrow around metaphase plate Membrane closes, producing daughter cells

132 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

133 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)

134 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

135 KEY CONCEPT All body cells, except sex cells, contain the same 46 chromosomes Differentiation depends on which genes are active and which are inactive

136 SUMMARY (1 of 4) Structures and functions of human cells
Structures and functions of membranous and nonmembranous organelles

137 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

138 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

139 SUMMARY (4 of 4) Stages and processes of cell division:
DNA replication mitosis cytokinesis

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