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Rod R. SeeleyIdaho State University

Trent D. StephensIdaho State University

Philip TatePhoenix College

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Chapter 03Chapter 03

Lecture OutlineLecture Outline**

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Chapter 3

Cell Biology and Genetics

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• Plasma membrane • Cytoplasm containing organelles • Nucleus

Basic Structure of the Cell

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• Cell metabolism and energy use• Synthesis of molecules• Communication. Cells produce and receive

electrical and chemical signals• Reproduction and Inheritance. Each cell contains

DNA. Some cells are specialized to gametes for exchange during sexual intercourse

Functions of the Cell

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Plasma Membrane• Separation of intracellular vs.

extracellular materials• Production of charge difference

(membrane potential) across the membrane by regulation of intracellular and extracellular ion concentrations– Outside of membrane positively

charged compared to inside because of gathering ions along outside and inside

• Glycocalyx: combinations of carbohydrates and lipids (glycolipids) and proteins (glycoproteins) on outer surface.

• Fluid-mosaic model

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Membrane Lipids• Phospholipids and cholesterol predominate

– Phospholipids: bilayer. Polar heads facing water in the interior and exterior of the cell (hydrophilic); nonpolar tails facing each other on the interior of the membrane (hydrophobic)

– Cholesterol: interspersed among phospholipids. Amount determines fluid nature of the membrane

• Fluid nature provides/allows

– Distribution of molecules within the membrane

– Phospholipids automatically reassembled if membrane is damaged

– Membranes can fuse with each other

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Membrane Proteins

• Integral or intrinsic – Extend deeply into membrane,

often extending from one surface to the other

– Can form channels through the membrane

• Peripheral or extrinsic– Attached to integral proteins at

either the inner or outer surfaces of the lipid bilayer

• Functioning depends on 3-D shape and chemical characteristics. Markers, attachment sites, channels, receptors, enzymes, or carriers.

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Marker Molecules: Glycoproteins and Glycolipids

• Allow cells to identify one another or other molecules – Immunity

– Recognition of oocyte by sperm cell

– Intercellular communication

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Attachment Proteins

• Cadherins – attach cells to other cells

• Integrins – integral proteins that attach to extracellular molecule – Sometimes allow

communication due to contact with intracellular molecules

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Transport Proteins

• Hydrophilic region faces inward; charge determines molecules that can pass through

• Includes channel proteins, carrier proteins, and ATP-powered pumps.

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Channel Proteins

• Nongated ion channels: always open– Responsible for the permeability of

the plasma membrane to ions when the plasma membrane is at rest

• Gated ion channels can be opened or closed by certain stimuli– Ligand gated ion channel: open in

response to small molecules that bind to proteins or glycoproteins

– Voltage-gated ion channel: open when there is a change in charge across the plasma membrane

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Carrier Proteins

• Also called transporters• Integral proteins move ions from

one side of membrane to the other– Have specific binding sites

– Protein changes shape to transport ions or molecules

– Resumes original shape after transport

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Carrier Proteins (cont.)

• Carrier proteins come in several forms– Uniporters – moves one particle

– Symporters – move two particles in the same direction at the same time

– Antiporters – move two particles in opposite directions at the same time

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ATP-Powered Transport• Requires ATP. The use of

energy allows the cell to accumulate substances

• Rate of transport depends on concentration of substrate and on concentration of ATP

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Receptor Proteins• Proteins or glycoproteins in membranes with an exposed

receptor site• Can attach to specific chemical signal molecules and act

as an intercellular communication system• Ligand can attach only to cells with that specific receptor

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Receptors Linked to Channel Proteins

• Receptor molecules linked to channel proteins

• Attachment of receptor-specific chemical signals (e.g., acetylcholine) to receptors causes change in shape of channel protein

• Channel opens or closes• Changes permeability of cell to some

substances– Cystic fibrosis: defect in genes

causes defect(s) in channel proteins– Drugs used to alter membrane

permeability through attachment to channel protein-linked receptors

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Receptors Linked to G Protein Complexes

• Alter activity on inner surface of plasma membrane

• Leads to intracellular chemical signals that affect cell function

• Some hormones function in this way

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Enzymes in the Plasma Membrane

• Enzymes: some act to catalyze reactions at outer/inner surface of plasma membrane. Surface cells of small intestine produce enzymes that digest dipeptides

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Summary of Membrane Proteins

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Movement through the Plasma Membrane

• Diffusion

• Osmosis

• Filtration

• Mediated Transport – Facilitated diffusion– Active transport– Secondary active transport

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Diffusion• Movement of solutes from an area of higher

concentration to lower concentration in solution– Concentration or density gradient: difference

between two points– Viscosity: how easily a liquid flows

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Osmosis

• Diffusion of water (solvent) across a selectively permeable membrane. Water moves from an area of low concentration of solute to an area of high concentration of solute

• Osmotic pressure: force required to prevent water from moving across a membrane by osmosis

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Osmosis• Comparative terms used

to describe osmotic pressures of solutions– Isosmotic: solutions with

the same concentrations of solute particles

– Solution with a greater concentration of solute is hyperosmotic

– Solution with a lesser concentration of solute is hyposmotic

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Osmosis and Cells• Important because large volume changes caused by water movement

disrupt normal cell function• Cell shrinkage or swelling

– Isotonic: cell neither shrinks nor swells– Hypertonic: cell shrinks (crenation)– Hypotonic: cell swells (lysis)

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Filtration• Works like a sieve• Depends on pressure difference on either side

of a partition• Moves from side of greater pressure to lower• Example: urine formation in the kidneys.

Water and small molecules move through the membrane while large molecules remain in the blood

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Mediated Transport

• Involve carrier proteins or channels in the cell membrane

• Characteristics– Specificity for a single type

of molecule

– Competition among molecules of similar shape

– Saturation: rate of transport limited to number of available carrier proteins

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Saturation of a Carrier Protein1. When the concentration of x molecules outside the cell is low, the transport

rate is low because it is limited by the number of molecules available to be transported.

2. When more molecules are present outside the cell, as long as enough carrier proteins are available, more molecules can be transported; thus, the transport rate increases.

3. The transport rate is limited by the number of carrier proteins and the rate at which each carrier protein can transport solutes. When the number of molecules outside the cell is so large that the carrier proteins are all occupied, the system is saturated and the transport rate cannot increase.

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Mediated Transport – Facilitated Diffusion

• Facilitated diffusion: carrier- or channel-mediated. Passive.– Move large, water

soluble molecules or electrically charged molecules across the plasma membrane.

– Amino acids and glucose in, manufactured proteins out.

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Mediated Transport – Active Transport

• ATP-Powered Transport– Requires ATP. The use of energy

allows the cell to accumulate substances

– Rate of transport depends on concentration of substrate and on concentration of ATP

– Example: Na+/K+ exchange pump that creates electrical potentials across membranes

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Mediated Transport – Secondary Active Transport

• Ions or molecules move in same (symport) or different (antiport) direction.

• Is the movement of glucose a symporter example or an antiporter example?

• This example shows cotransport of Na+ and glucose. 1. A sodium-potassium exchange

pump maintains a concentration of Na that is higher outside the cell than inside. Active transport.

2. Na moves back into the cell by a carrier protein that also moves glucose. The concentration gradient for Na provides the energy required to move glucose against its concentration gradient.

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Endocytosis• Internalization of substances by formation of a vesicle• Types

– Phagocytosis (shown)– Pinocytosis– Receptor-mediated endocytosis

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Pinocytosis and Receptor-Mediated Endocytosis

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Exocytosis

• Accumulated vesicle secretions expelled from cell• Examples

– Secretion of digestive enzymes by pancreas

– Secretion of mucous by salivary glands

– Secretion of milk by mammary glands

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Cytoplasm• Cellular material outside

nucleus but inside plasma membrane

• Composed of Cytosol, Cytoskeleton, Cytoplasmic Inclusions, Organelles

• Cytosol: fluid portion. Dissolved molecules (ions in water) and colloid (proteins in water)

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Cytoskeleton• Supports the cell but has to allow for

movements like changes in cell shape and movements of cilia

– Microtubules: hollow, made of tubulin.

• Internal scaffold, transport, cell division

– Microfilaments: actin. • Structure, support for microvilli,

contractility, movement

– Intermediate filaments: mechanical strength

• Cytoplasmic inclusions: aggregates of chemicals such as lipid droplets, melanin

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Organelles

• Small specialized structures with particular functions

• Most have membranes that separate interior of organelles from cytoplasm

• Related to specific structure and function of the cell

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Nucleus• Membrane-bound• Nucleoplasm, nucleolus and nuclear envelope• Much of the DNA in a cell located here

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Chromosome Structure

• Chromatin: DNA complexed with proteins (histones)

• During cell division, chromatin condenses into pairs of chromatids called chromosomes. Each pair of chromatids is joined by a centromere

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Ribosomes• Sites of protein synthesis• Composed of a large and

a small subunit• Types

– Free

– Attached (to endoplasmic reticulum)

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Endoplasmic Reticulum• Types

– Rough• Has attached ribosomes• Proteins produced and modified here

– Smooth• No attached ribosomes• Manufactures lipids

• Cisternae: Interior spaces isolated from rest of cytoplasm

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Golgi Apparatus

• Modification, packaging, distribution of proteins and lipids for secretion or internal use

• Flattened membrane sacs stacked on each other

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Function of Golgi Apparatus

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Action of Lysosomes

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Peroxisomes and Proteasomes• Peroxisomes

– Smaller than lysosomes– Contain enzymes to break down fatty acids and

amino acids– Hydrogen peroxide is a by-product of

breakdown

• Proteasomes– Consist of large protein complexes– Include several enzymes that break down and

recycle proteins in cell

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Mitochondria

• Major site of ATP synthesis• Membranes

– Cristae: Infoldings of inner membrane

– Matrix: Substance located in space formed by inner membrane

• Mitochondria increase in number when cell energy requirements increase.

• Mitochondria contain DNA that codes for some of the proteins needed for mitochondria production.

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Centrioles and Spindle Fibers

• Located in centrosome: specialized zone near nucleus

• Center of microtubule formation

• Before cell division, centrioles divide, move to ends of cell and organize spindle fibers

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Cilia• Appendages projecting from cell surfaces• Capable of movement• Moves materials over the cell surface

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Flagella

• Similar to cilia but longer

• Usually only one per cell

• Move the cell itself in wave-like fashion

• Example: sperm cell

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Microvilli• Extension of plasma membrane• Increase the cell surface area• Normally many on each cell• One tenth to one twentieth size of cilia• Do not move

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Genes and Gene Expression

• Gene– Functional unit of heredity– Types

• Structural: serve as template for mRNA, code for amino acid sequences

• Regulatory: control which structural genes transcribed in given tissue

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Genes and Gene Expression• Transcription: DNA used to form RNA• Translation: synthesis of a protein at the ribosomes

using mRNA, tRNA and rRNA

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Transcription• The strands of DNA are

separated• RNA polymerase binds at a

promoter region• RNA polymerase catalyses

the formation of a mRNA chain using the DNA as a template and following the rules of complimentary base pairing– A with U – C with G

• Transcription ends at a terminator sequence

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Posttranscription Processing• The mRNA is modified after

transcription and before it can leave the nucleus– Intron removal

– Guanosine cap added

– Poly-A tail added

• The mRNA now contains the genetic code that will be used to manufacture a polypeptide

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Translation

• Process that occurs on ribosomes

• Turns mRNA into a polypeptide

• Involves rRNA, tRNA, and mRNA

• tRNA anticodons match with mRNA codons, and the rRNA catalyzes the formation of a peptide bond between the amino acids at the opposite end of the tRNA

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Regulation of Protein Synthesis

• All nucleated cells except germ cells have the full complement of DNA.

• During development, differentiation occurs and some segments of DNA are turned off in some cells while those segments remain “on” in other cells.

• During the lifetime of a cell, the rate of protein synthesis varies depending upon chemical signals that reach the cell.– Example: thyroxine from the thyroid causes cells to

increase their metabolic rate. More thyroxine, higher metabolic rate; less thyroxine, lower metabolic rate.

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Cell Life Cycle• Interphase: phase between cell

divisions– Replication of DNA– Ongoing normal cell activities

• Mitosis: series of events that leads to the production of two cells by division of a mother cell into two daughter cells. Cells are genetically identical.– Prophase– Metaphase– Anaphase– Telophase

• Cytokinesis: division of cell cytoplasm

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Replication of DNA• DNA strands separate• The old strands become the templates for the new

(complementary) strands to form• Two identical DNA molecules are formed by semiconservative

replication

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Mitosis• Interphase – DNA replication

occurs• Mitosis

– Prophase – nuclear envelope disintegrates, chromatin condenses, spindles attach to kinetochore

– Metaphase – chromosomes are aligned at the nuclear equator

– Anaphase – spindles separate the chromatids, cytokinesis begins

– Telophase – chromosomes decondense, nuclear envelope reforms, cytokinesis continues

• Cytokinesis – cytoplasmic division, separate process from mitosis

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Genetics

• Study of heredity

• Explains how certain characteristics are passed on to offspring

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Mendalian Genetics

• Genotype: actual set of alleles a person has for a given trait

• Phenotype: person’s appearance

• Dominant and recessive alleles– Dominant masks effects of recessive genes

• Sex-linked traits: traits affected by genes on sex chromosomes

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Mendalian Genetics

• Homozygous: Having two of the same alleles for a trait.– Homozygous dominant: AA– Homozygous recessive: aa

• Heterozygous: Having one dominant and one recessive allele for a trait– Aa

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Chromosomes• Genetics: study of heredity• DNA: hereditary material of

cells and controls cell activities• Found in discrete sections

called chromosomes– Karyotype or display– Autosomal and sex (X or Y)– Contain thousands of genes

• Diploid: two copies of chromosomes

• Haploid: one copy of chromosomes, only in gametes

• Karyotype: map of chromosomes

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Inheritance of Sex

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Chromosomes

• Homologous: pairs of chromosome where one is from the father and the other is from the mother

• Locus: the location of a gene on a chromosome

• Allele: different forms of the same gene– Multiple alleles –

sometimes alleles come in more than just dominant and recessive forms

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Gene Dominance

• Complete dominance: the dominant allele covers up the recessive allele and is the only allele expressed

• Codominance: both alleles are expressed equally at the same time

• Incomplete dominance: the dominant allele and the recessive allele both are expressed, with the recessive being at a much lower level

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Other Types of Gene Expression

• Polygenic traits– Determined by

expression of multiple genes on different chromosomes

– Height, eye and skin color, intelligence

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Sex-linked Traits

• Affected by areas of the X and Y chromosome

• X-linked traits more often affect males

• Y-linked traits only affect males

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Meiosis and the Transmission of Genes

• Meiosis: DNA replication followed by two cell divisions

• Homologous pairs are separated

• Resulting gametes (egg, sperm) unite to form a zygote

• Homologous pairs are reunited– New pairs are a mixture of

DNA from two individuals

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Genetic Disorders• Genetic disorders:

abnormalities in DNA• Congenital disorders

– Birth defects not necessarily genetic

– Teratogens: agents that cause birth defects

• Mutation– Mutagens: agents that

cause mutations

• Cancer: tumor resulting from uncontrolled cell divisions– Oncogenes: genes

associated with cancer

– Tumor suppressor genes

– Carcinogens

– Genetic susceptibility or predisposition