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Chapter 3

Cell Structure and Function

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Cell structure and function Outline• Cellular Organization

– Plasma MembraneFunctions

– NucleusCell division and protein synthesis (ch.

19 and 18)– Endomembrane System– Cytoskeleton– Cilia and Flagella

• Cellular Respiration• Fermentation

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Cellular Organization

• Plasma membrane surrounds the cell and regulates entrance and exit of substances.– Nucleus is the centrally located structure

containing chromosomes and is the control center of the cell.

– Cytoplasm is the portion of the cell between the nucleus and plasma membrane.

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Cellular Organization

– Organelles are small membranous structures, each with a specific function.

– Cytoskeleton is a network of interconnected filaments and microtubules in the cytoplasm that maintain cell shape.

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Plasma Membrane• Plasma membrane is a phospholipid bilayer with

attached or embedded proteins.– Polar head and non-polar tails.

Form spherical bilayer when placed in water.– Plasma membrane proteins form receptors,

conductors, or enzymes in metabolic reactions.

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Plasma Membrane Model

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Plasma Membrane Functions

• Plasma membrane is selectively permeable, and regulates movement of molecules and ions across the cell membrane.– Diffusion is the random movement of

molecules from an area of higher concentration to an area of lower concentration until they are equally distributed.

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Plasma Membrane Functions

– Osmosis is the diffusion of water across a plasma membrane.

Tonicity is the degree to which a solution’s solute concentration causes water to move into or out of cells.

Cells gain water in hypotonic solutions, and lose water in hypertonic solutions.

Osmotic pressure is the force exerted on a selectively permeable membrane due to the osmotic movement of water.

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Tonicity= # of solute particles dissolved per set volume

# solutes particles outside equals inside

For diagram b. # of solute particles outsideis lower than insideThus solvent outside is higher/lower (circle one) than Solvent inside

For diagram cSolvent outside is hiher/lower (circle one) thanSolvent inside

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Plasma Membrane Functions

– Transport by Carriers.Maintains cellular homeostasis

(membrane proteins create selective permeability)

Facilitated transport occurs when a molecule is transported across the plasma membrane down a concentration gradient.

Active transport occurs when a molecule is moving against a concentration gradient with the input of energy.

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Active Transport- things that normally do not get across the cell membrane

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Plasma Membrane Functions

– Transport by Carriers.Endocytosis occurs when a portion of the

plasma membrane invaginates to envelop a substance and then pinches off to form an intracellular vesicle.

Exocytosis occurs when a vesicle fuses with the plasma membrane as secretion occurs.

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The Nucleus

• The nucleus stores genetic information that determines body cell characteristics and metabolic functioning.

• Nucleus is separated from the cytoplasm by a nuclear envelope.

Contains nuclear pores to permit passage of proteins and ribosomal subunits.

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Ch. 19 DNA and RNA Structure and Function

• DNA is the genetic material found principally in chromosomes.– In between cell divisions, chromosomes

exist in long fine threads of chromatin.When a cell is about to divide,

chromosomes coil and condense.

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DNA Location and Structure

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DNA Structure and Replication

• DNA is a sequential series of joined nucleotides.– Sugar (deoxyribose), phosphate, and base.

Adenine (A).Thymine (T).Cytosine (C).Guanine (G).

nucleotides

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DNA Structure and Replication

• DNA is a double helix with a sugar-phosphate backbone and bases projecting between the backbones.– Exhibits complementary base pairing.

A-T.G-C.

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DNA Replication- for cell reproduction/division

• Replication Steps.– Hydrogen bonds between strands break

and the molecule unzips.– New nucleotides fit beside parental

strand.– DNA polymerase joins new nucleotides.– Two complete molecules present, each

with one old strand and one new strand.Semi-conservative replication.

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DNA Replication/ cell division Mitosis and Meiosis (replacing cells or making babies)

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Structure and Function of RNA- protein synthesis (the way we look)

• RNA is made up of nucleotides containing the sugar ribose and the base uracil in place of thymine.– Single stranded.

RNA is a helper to DNA allowing protein synthesis.

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Types of RNA

• Ribosomal RNA.– Joins with proteins made in the cytoplasm

to form the subunits of ribosomes.• Messenger RNA.

– Carries genetic information from DNA to the ribosomes in the cytoplasm where protein synthesis occurs.

• Transfer RNA.– Transfers amino acids to the ribosomes

where amino acids are joined.

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Gene Expression

• Structure and Function of Proteins.

– Proteins are composed of amino acids.

Proteins differ because the number and order of their amino acids differ.

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DNA Code

• Genetic code is essentially universal.– Contains a triplet code.

Every three bases represents one amino acid.

• Transcription.– Strand of mRNA forms that is

complementary to a portion of DNA.Triplet of mRNA is termed a codon.

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Processing of mRNA

• Most human genes are interrupted by introns.– Intragene segments interrupt gene

segments, exons.During processing, introns are removed

and exons are joined to form an mRNA molecule.

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Function of Introns

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Translation

• Translation is the synthesis of a polypeptide under the direction of an mRNA molecule.– Transfer RNA molecules bring amino

acids to the ribosomes.Anticodon is triplet complementary to

an mRNA codon.• Polypeptide synthesis requires three steps.

– Initiation.– Elongation.– Termination.

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Anticodon-Codon Base Pairing this occurs in cytoplasm or an endoplasmic reticulum

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Regulation of Gene Expression

• Gene Regulation Mechanisms.– Transcriptional control.– Posttranscriptional control.– Translational control.– Posttranslational control.

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Ch. 18 Genotype and Phenotype

• Genotype refers to an individual’s genes.– Alleles are alternate forms of a gene.

Dominant alleles are assigned uppercase letters, while recessive alleles are assigned lowercase letters.

Homozygous Dominant = EE. Homozygous Recessive = ee. Heterozygous = Ee.

• Phenotype refers to an individual’s physical appearance.

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Genetic Inheritance

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Dominant/Recessive Traits

• Forming the Genes.– Reduction of chromosome number occurs

when pairs of chromosomes separate as meiosis occurs.

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Gametogenesis

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Nucleus and Nuclear Membrane

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Ribosomes

• Ribosomes are found singly or in groups (polyribosomes) in the cytoplasm.– Function in protein synthesis.

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The Endomembrane System- also function in protein synthesis

• Endoplasmic Reticulum.– System of membranous channels and

saccules.Rough ER is studded with ribosomes

and synthesizes proteins.Smooth ER synthesizes phospholipids,

as well as various other functions.

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The Endomembrane System- process final products and monitor incoming vesicles

• The Golgi Apparatus.– Consists of a stack of three to twenty

curved saccules, along with vesicles.Receives protein and or lipid vesicles

that bud from the ER.• Lysosomes.

– Membranous sacs produced by the Golgi apparatus that contain hydrolytic digestive enzymes.

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Endomembrane System

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Mitochondria- The “powerhouse”

• Mitochondria are double-membrane organelles involved in cellular respiration.– Site of ATP production.

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The Cytoskeleton

• The cytoskeleton is formed of several types of filamentous structures that give the cell its shape and organelles the ability to move about the cell.– Microtubules.– Actin Filaments.

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Centrioles

• Centrioles are short cylinders composed of microtubules that are involved in spindle formation during cell division

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Cilia and Flagella

• Cilia and flagella (cilium, flagellum) are projections that move in an undulating or whipping fashion.– Cilia tend to be shorter while flagella tend

to be longer.

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Cellular Metabolism

• Cellular metabolism includes all the chemical reactions that occur in a cell.– Often organized into metabolic pathways.

Most regulated by feedback inhibition.

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Enzymes and Coenzymes

• When an enzyme speeds up a reaction, the participating reactants are called the enzyme’s substrates.– Many enzymes require cofactors for

assistance.Some cofactors may accept or donate

atoms to the reaction.

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Enzymatic Action

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Cellular Respiration

• Glucose breakdown requires three sub-pathways.– Glycolysis.– Citric Acid Cycle.– Electron Transport System.

• Altogether, the breakdown of one glucose molecule results in 36 ATP molecules.

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Cellular Respiration

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Fermentation

• Fermentation is an anaerobic process that results in the buildup of lactate.– Lactate is toxic to cells and causes

muscle cramps and fatigue.– Only produces two ATP per glucose

molecule.

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Lecture Review

• Describe the function and structure of the cell membrane.

• Define isotonic, hypotonic and hypertonic solutions.

• Describe the nucleus and its contents including the process of protein sysnthesis and cell reproduction (cell division- mitosis and meiosis).

• Describe cell metabolism (cell respiration) anaerobic and aerobic

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