Transcript A View of Life

Chapter 3
Cell Structure and Function
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Cell structure and function Outline
Cellular Organization
– Plasma Membrane
 Functions
– Nucleus
 Cell division and protein synthesis (ch.
19 and 18)
– Endomembrane System
– Cytoskeleton
– Cilia and Flagella
Cellular Respiration
Fermentation
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Cellular Organization
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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
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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
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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
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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
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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
For diagram b.
# of solute particles outside
is lower than inside
Thus solvent outside is higher/lower (circle one) than
Solvent inside
For diagram c
Solvent outside is
hiher/lower (circle
one) than
Solvent inside
# solutes particles outside equals inside
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Plasma Membrane Functions
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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
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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
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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
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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
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DNA is a sequential series of joined
nucleotides.
– Sugar (deoxyribose), phosphate, and base.
 Adenine (A).
 Thymine (T).
nucleotides
 Cytosine (C).
 Guanine (G).
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DNA Structure and Replication
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DNA is a double helix with a sugarphosphate 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
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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)
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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
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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
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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
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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
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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
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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
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Gene Regulation Mechanisms.
– Transcriptional control.
– Posttranscriptional control.
– Translational control.
– Posttranslational control.
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Ch. 18 Genotype and Phenotype
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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
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appearance.
Genetic Inheritance
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Dominant/Recessive Traits
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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
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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
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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
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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”
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Mitochondria are double-membrane
organelles involved in cellular respiration.
– Site of ATP production.
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The Cytoskeleton
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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
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Centrioles are short cylinders composed of
microtubules that are involved in spindle
formation during cell division
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Cilia and Flagella
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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
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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
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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
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Glucose breakdown requires three subpathways.
– 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
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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
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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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