Chapter 3 Cells Structure Function Cell Theory Cells

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Chapter 3 Cells Structure & Function

Chapter 3 Cells Structure & Function

Cell Theory Cells are the building blocks of the human body 4 concepts of

Cell Theory Cells are the building blocks of the human body 4 concepts of the cell theory: Ë Cells are the building blocks of all plants and animals Ë Cells are the smallest functioning units of life Ë Ë Cells are produced through the division of preexisting cells Each cells maintain homeostasis

The Study of Cells and Their Anatomy Cytology – the study of the structure

The Study of Cells and Their Anatomy 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: Ë Extracellular fluid – watery medium surrounding cells Ë In tissues it’s called interstitial fluid Plasma (Cell) membrane – separates the cell contents (cytoplasm) from extracellular fluid Ë Nucleus – control center for cellular operations Ë Cytoplasm subdivides into: Cytosol – liquid in cell Organelles – intracellular structures

Chromatin Nucleolus Nuclear envelope Nucleus Smooth endoplasmic reticulum Mitochondrion Cytosol Lysosome Centrioles Centrosome matrix

Chromatin Nucleolus Nuclear envelope Nucleus Smooth endoplasmic reticulum Mitochondrion Cytosol Lysosome Centrioles Centrosome matrix Cytoskeletal elements • Microtubule • Intermediate filaments Copyright © 2010 Pearson Education, Inc. Plasma membrane Rough endoplasmic reticulum Ribosomes Golgi apparatus Secretion being released from cell by exocytosis Peroxisome Figure 3. 2

Plasma Membrane General functions include: Ë Physical isolation Ë Regulation of exchange with the

Plasma Membrane General functions include: Ë Physical isolation Ë Regulation of exchange with the environment Ë Controls the entry of ions and nutrients, the elimination of wastes, and the release of secretions Sensitivity to the environment Ë A physical barrier that separates the inside of the cell from the extracellular fluid Contains a variety of receptors that enable the cell to recognize and respond to specific molecules in the environment Structural support For tissues

Hydrophilic head of phospholipid molecule Extracellular fluid (watery environment) Cholesterol Glycolipid Glycoprotein Carbohydrate of

Hydrophilic head of phospholipid molecule Extracellular fluid (watery environment) Cholesterol Glycolipid Glycoprotein Carbohydrate of glycocalyx Outward-facing layer of phospholipids Integral proteins Filament of cytoskeleton Peripheral Bimolecular proteins lipid layer containing Hydrophobic proteins tail of Cytoplasm (watery environment) Copyright © 2010 Pearson Education, Inc. phospholipid molecule Figure 3. 3

Plasma Membrane Lipids v Phosphate heads: polar and hydrophilic v Fatty acid tails: nonpolar

Plasma Membrane Lipids v Phosphate heads: polar and hydrophilic v 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 v Lipid-soluble molecules, oxygen, CO 2, etc. are able to cross v Ions and water-soluble compounds cannot Membrane Proteins The phospholipids in a plasma membrane lie in 2 distinct layers: (phospholipid bilayer) 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 Filtration The permeability of the plasma membrane is the property that determines

Diffusion and Filtration The permeability of the plasma membrane is the property that determines precisely which substances can enter or leave the cytoplasm. Ë If nothing can cross a membrane, it’s impermeable Ë If any substance can cross without difficulty, it’s freely permeable Ë Plasma membranes are selectively permeable Based on size, charge, shape, solubility Movement is either passive or active Ë Passive – move ions or molecules across the plasma membrane without any energy expenditure by the cell Diffusion Ë Ë Osmosis Filtration Active – require that the cell expend energy, usually in the form of ATP

Diffusion The net movement of molecules from an area of relatively high concentration to

Diffusion The net movement of molecules from an area of relatively high concentration to an area of relatively low concentration Ë The different areas create a concentration gradient Ë Movement happens until the gradient no longer exists Diffusion Across Plasma Membranes Ë Ë 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

Osmosis The diffusion of water across a membrane Because dissolved solute molecules occupy space

Osmosis 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 Ë 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: Ë Ë Ë 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. ) The osmotic pressure of a solution is an indication of the

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 Ë 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)

Filtration In this passive process, hydrostatic pressure forces water across a membrane If solute

Filtration 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 Transport Requires the presence of specialized membrane proteins It can be passive (no

Carrier-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. ) Facilitated Diffusion Ë Used when essential nutrients are insoluble in

Carrier-Mediated Transport (cont. ) Facilitated Diffusion Ë 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 Ë Ë Ë 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 +, Ca 2+, and Mg 2+ 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

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 Transport Involves the movement of materials within small membranous sacs called vesicles Always

Vesicular Transport Involves the movement of materials within small membranous sacs called vesicles Always an active process 2 major categories: Ë Endocytosis – the packaging of extracellular materials in a vesicle at the cell surface for import into the cell Ë 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 Cytosol Cytoplasm is a general term for material inside the cell including the

The 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: Ë Ë Ë 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 Organelles Internal structures that perform specific functions essential to normal cell structure, maintenance,

The Organelles Internal structures that perform specific functions essential to normal cell structure, maintenance, and metabolism Ë Cytoskeleton – internal protein framework of various threadlike filaments and hollow tubules that gives the cytoplasm strength and flexibility Ë Ë 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. ) Ë Ë Ë Ribosomes – manufacture proteins using information provided

The Organelles (cont. ) Ë Ë Ë 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 Ë 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. ) Ë Ë Lysosomes – filled with digestive enzymes. Perform cleanup

The Organelles (cont. ) Ë Ë 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 functions it can perform by controlling which proteins synthesized, under what circumstances, and in what amounts

Transcription and Translation Transcription – the production of m. RNA from a single strand

Transcription and Translation Transcription – the production of m. RNA from a single strand of DNA Ë Takes place in the nucleus Ë Steps: RNA polymerase binds to the promoter of a gene Promotes the synthesis of an m. RNA strand using complementary nucleotides A sequence of 3 nitrogenous bases along the new m. RNA strand represents a codon that corresponds to a triplet on the gene At the DNA “stop” signal the m. RNA detaches Translation – the assembling of a protein by ribosomes, using the information carried by the RNA molecule Ë Takes place in the cytoplasm Ë Steps: Begins at the “start” codon of m. RNA (AUG) with the attachment of the first t. RNA carrying an amino acid The small and large ribosomal subunits join together to enclose the m. RNA A second t. RNA arrives, carrying a different amino acid, and binds to the next codon Ribosomal enzymes remove AA 1 from its t. RNA and attach it to AA 2 with a peptide bond This continues until it reaches the “stop” codon, where the strand detaches

Nuclear envelope Transcription RNA Processing DNA Pre-m. RNA Translation Polypeptide Nuclear pores Ribosome

Nuclear envelope Transcription RNA Processing DNA Pre-m. RNA Translation Polypeptide Nuclear pores Ribosome

Nucleus Energized by ATP, the correct amino acid is attached to each species of

Nucleus Energized by ATP, the correct amino acid is attached to each species of t. RNA by aminoacyl-t. RNA synthetase enzyme. RNA polymerase m. RNA Leu Template strand of DNA 1 After m. RNA synthesis in the nucleus, m. RNA leaves the nucleus and attaches to a ribosome. Amino acid Nuclear pore t. RNA Nuclear membrane 2 Translation begins as incoming aminoacyl-t. RNA recognizes the complementary codon calling for it at the A site on the ribosome. It hydrogen-bonds to the codon via its anticodon. G A A Released m. RNA Aminoacyl-t. RNA synthetase Leu 3 As the ribosome moves along the m. RNA, and each codon is read in sequence, a new amino acid is added to the growing protein chain and the t. RNA in the A site is translocated to the P site. Ile G Pro 4 Once its amino acid is released from the P site, t. RNA is ratcheted to the E site and then released to reenter the cytoplasmic pool, ready to be recharged with a new amino acid. The polypeptide is released when the stop codon is read. U A A A U E site P site G G C A site A U A C C G C U U Codon 15 Codon 17 Codon 16 Direction of Portion of m. RNA ribosome advance already translated Large ribosomal subunit Small ribosomal subunit t. RNA “head” bearing anticodon

SECOND BASE C A U UUU U UUC A UAU UCC UAC Ser UGC

SECOND BASE C A U UUU U UUC A UAU UCC UAC Ser UGC Cys U C UCG CUU CCU CAU CUC CCC CAC CUA Leu UCA CCA Pro UAA CUG CCG CAG AUU ACU AAU ACC AAC AUC Ile AUA ACA Thr Met or AUG Start ACG G Tyr UGU Stop UGA Stop A UAG Stop UGG Trp G UUA UUG C Phe UCU G AAA AAG GUU GCU GAU GUC GCC GAC GUA GUG Val GCA GCG Ala GAA GAG His Gln Asn Lys Asp Glu CGU U CGC C CGA Arg A CGG G AGU U AGC AGA AGG Ser Arg C A G GGU U GGC C GGA GGG Gly A G

Cell Life Cycle The duplication of a cell’s genetic material is called DNA replication,

Cell Life Cycle The duplication of a cell’s genetic material is called DNA replication, and nuclear division is called mitosis (only in somatic cells) Ë Sex cells = meiosis Stages: Ë Interphase – where cells spend most of their lives, an interval of time in which they perform normal functions Ë Ë Ë Four subphases: Ë G 1 (gap 1)—vigorous growth and metabolism Ë G 0—gap phase in cells that permanently cease dividing Ë S (synthetic)—DNA replication Ë G 2 (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

G 1 checkpoint (restriction point) S Growth and DNA synthesis G 1 Growth M

G 1 checkpoint (restriction point) S Growth and DNA synthesis G 1 Growth M G 2 Growth and final preparations for division G 2 checkpoint