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Chapter 3
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Functions
• Basic unit of life
• Synthesis of molecules
• Communication
• Cell metabolism and energy release
• Reproduction and inheritance (DNA)
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Cell Structure
• Organelles:
- specialized structures in cells that perform
specific functions
- Ex. Nucleus, mitochondria, ribosomes, etc.
• Cytoplasm:
jelly-like substance that holds organelles
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Cell Membrane
• What is it?
outermost component of a cell
• Functions:
- selective barrier
- encloses cytoplasm
• Extracellular: material outside cell
• Intracellular: material inside cell
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Structure of Cell Membrane
• Called Fluid Mosaic Model
• Made of phospholipids and proteins
• Phospholipids form a double layer or bilayer
• Phospholipids contain 2 regions: polar and
nonpolar
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• Polar regions:
- “heads”
- hydrophilic (H2O loving)
- exposed to H2O
• Nonpolar regions:
- “tails”
- hydrophobic (H2O fearing)
- away from H2O
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Figure 2.14b
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Figure 3.2a
Movement through Cell Membrane
• Cell membrane selectively determines what can
pass in and out of the cell.
• Enzymes, glycogen, and potassium are found in
higher concentrations INSIDE the cell.
• Sodium, calcium, and chloride are found in higher
concentrations OUTSIDE the cell.
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Ways molecules Pass through Cell Membrane
1. Directly through (diffusion):
O2 and CO2 (small molecules)
2. Membrane channels:
- proteins that extend from one side of cell
membrane to other
- size, shape, and charge (+/-) determine what can
go through
- Ex. Na+ passes through Na+ channels
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3. Carrier molecules:
- bind to molecules, transport them across, and
drop them off
- Ex. glucose
4. Vesicles:
- can transport a variety of materials
- fuse with cell membrane
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Figure 3.7
Diffusion
• What is it?
movement of molecules from areas of high to low
concentration
• Solution:
solid, liquid, or gas that contains one or more solutes
• Solute:
substance added to solvent that dissolves
• Solvent:
substance such as H2O that solute is being added to
Ex. Add salt to H2O. H2O =solvent, salt=solute,
mixture=solution
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• Concentration gradient:
- measures conc. difference at 2 points
- greater the distance the faster the solute
will travel
• Filtration:
movement of fluid through a partition with holes
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Mediated Transport Mechanisms
•
Facilitated diffusion:
- diffusion with aid of a carrier molecule
- requires no ATP
•
Active transport:
- moves substances from low to high conc.
- requires ATP
- Ex. Sodium-potassium pump
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Osmosis
• What is it?
diffusion of water across a cell membrane
• Osmotic pressure:
force required to prevent movement of water across
cell membrane
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Types of Osmotic Solutions
• Hypotonic solution:
- lower conc. of solutes outside cell
- higher conc. of H2O outside cell
- H2O moves into cell
- lysis (burst)
• Hypertonic solution:
- higher conc. of solutes outside cell
- higher conc. H2O inside cell
- H2O moves out
- crenation (shrinks)
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• Isotonic solution:
- equal conc. of solutes
- water doesn’t move
- cell remains intact
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Endocytosis
• What is it?
process that brings materials into cell using
vesicles
• 2 types
- Phagocytosis:
cell eating (solid particles)
- Pinocytosis:
cell drinking (liquid particles)
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Exocytosis
• What is it?
process that carries materials out of cell
using vesicles
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Cell Structures
• Cytoplasm
Location: inside cell
Characteristic: jelly-like fluid
Function: give cell shape and hold organelles in
place
• Nucleus
Location: center of cell
Characteristic: all cells contain nucleus at some
point
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Function: houses DNA
• Nuclear envelope:
Location: edge of nucleus
• Nuclear pores:
Location: surface of nucleus
Function: where materials pass in and out of
nucleus
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Figure 3.12a
• Chromosome:
Location: inside nucleus
Characteristic: made of DNA and proteins
Function: part of genetic makeup
• Chromatin:
Location: inside nucleus
Characteristic: loosely coiled chromosomes
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• Nucleolus
Location: in nucleus
Function: produce ribosomes
• Ribosome
Location: attached to RER or cytoplasm
Function: produce proteins
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• RER (Rough Endoplasmic Reticulum)
Location: cytoplasm
Characteristic: membranes with ribosomes attached
Function: site of protein synthesis
• SER (Smooth Endoplasmic Reticulum)
Location: cytoplasm
Characteristic: membranes with no ribosomes
Function: site of lipid synthesis (Ex. Cholesterol)
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Figure 3.15a
• Golgi apparatus
Location: cytoplasm
Characteristic: closely, packed stacks of
membranes
Function: collect, sort, package, and distribute
proteins and lipids
• Secretory vesicle
Location: cytoplasm
Function: distributes materials out of cell
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• Lysosome
Location: cytoplasm
Function: enzymes that digest foreign material
• Mitochondria
Location: cytoplasm
Characteristic: contains folds (cristae)
Function: produces ATP
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• Cilia
Location: cell surface
Characteristic: many per cell
Function: move materials across cell’s surface
• Flagella
Location: cell surface
Characteristic: 1 per cell
Function: move cell, Ex. sperm
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• Microvilli
Location: cell surface
Characteristic: shorter than cilia
Function: increase surface area
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Cytoskeleton
• What is it?
- cell’s framework
- made of proteins
• Functions:
- provide support
- hold organelles in place
- enable cell to change shape
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Types of Cytoskeleton
• Microtubules:
- largest diameter
- provide structural support
- form cilia and flagella
• Intermediate filaments:
- medium diameter
- maintain cell shape
• Microfilaments:
- smallest diameter
- involved in cell movement
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Whole Cell Activity
• A cell’s characteristics are determine by the
type of proteins produced
• Proteins’ function is determined by genetics
• Information in DNA provides the cell with a
code for its cellular processes
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DNA
• What is it?
- double helix in nucleus
- composed of nucleotides
- contains 5 carbon sugar (deoxyribose,
nitrogen base, phosphate
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Flow of Genetic Information
• Also called Central Dogma
• Occurs in three stages:
– DNA replication
– Transcription
– Translation
DNA
Replication
Gene Expression
• What is it?
- information in DNA directs protein
synthesis
- proteins provide code for gene expression
- enzymes regulate chemical reactions
- uses transcription and translation
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Transcription
• What is it?
- process by which DNA is “read”
- occurs in ribosomes
- produces mRNA (messenger RNA)
- mRNA contains codons
- codons: set of 3 nucleotide bases that code for
a particular amino acid
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Translation
• What is it?
- process by mRNA is converted into amino
acids (polypeptides)
- produces proteins
- codons pair with anticodons
- anticodons: 3 nucleotide bases carried by tRNA
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Cell Division
• What is it?
- formation of 2 daughter cells from a single
parent cell
- uses mitosis and meiosis
- each cell (except sperm and egg) contains
46 chromosomes (diploid)
- sperm and egg contain 23 chromosomes
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Mitosis
• What is it?
- cell division that occurs in all cells except
sex cells
- forms 2 daughter cells
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Components of Mitosis
• Chromatid:
2 strands of chromosomes that are genetically
identical
• Centromere:
where 2 chromatids are connected
• Centrioles:
small organelle composed of 9 triplets
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Stages in Mitosis
1. Interphase:
- time between cell divisions
- DNA is in strands (chromatin)
- DNA replication occurs
2. Prophase:
- chromatin condenses into chromosomes
- centrioles move to opposite ends
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3. Metaphase:
chromosomes align
4. Anaphase:
- chromatids separate to form 2 sets of
chromosomes
- chromosomes move towards centrioles
5. Telophase:
- chromosomes disperse
- nuclear envelopes and nucleoli form
- cytoplasm divides to form 2 cells
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