Cell Structure and Function
Chapter 3
Basic Characteristics of Cells
• Smallest living
subdivision of the human
body
• Diverse in structure and
function
• Small
Basic Characteristics of Cells
• Divided into organelles
– Structures and
compartments in the cell
– Isolation of chemical
reactions
– Each organelle performs a
specific function
Each Cell Has Three Primary
Regions
• Plasma Membrane
• Cytoplasm
• Nucleus
The Plasma Membrane
• Plasma membrane = outer casing of the
cell
– separates intracellular environment from the
extracellular environment.
• Regulates movement of materials into and
out of cell
– a selective mechanical barrier
The Plasma Membrane
• Composed of Lipids,
Proteins and
Carbohydrates
– Arranged in a lipid
bilayer
– “Fluid mosaic model”
Cell Membrane Components:
Phospholipids
• one end is hydrophilic
• other end is
hydrophobic
• tend to aggregate in a
lipid bilayer
– hydrophilic ends face
outward, hydrophobic
ends in the middle
Cell Membrane Components:
Proteins
• Suspended in lipid
bilayer
• May span layer or
attached only to one
surface
• Different functions
Types of Membrane Proteins
• Structural Proteins
– Maintain membrane shape
and integrity, movement
• Channel Proteins
– Pore-like proteins
– Enable small ions to pass
• Carrier proteins
– Shuttle specific substances
across membrane
Types of Membrane Proteins
• Enzymes
– Catalyze specific
reactions
• Receptor proteins
– Bind cellular signals
• Signaling proteins /
Recognition proteins
– Enable cells to identify
and interact with each
other
Cell Membrane Components:
Carbohydrates
• Branched polymers
attached to
extracellular surface
• Forms “sugar coating”
(glycocalyx) of cells
• Functions
– Lubricated surface
– Protect underlying
proteins
– Cell recognition
The Cytoplasm
Cytosol
• semi-liquid, gel-like
• contains various
dissolved materials,
enzymes, etc.
• cytoskeleton =
network of protein
fibers throughout
cytosol
– structure
– movement
Cytoplasmic Organelles:
Ribosomes
• Large protein-RNA
complexes
• Found free floating in
cytosol or attached to
endoplasmic
reticulum
• synthesize proteins
based on RNA codes
Cytoplasmic Organelles:
Endoplasmic Reticulum (ER)
• Rough Endoplasmic
Reticulum (RER)
– Coated with ribosomes
– Synthesis of proteins for:
• Cell membranes
• Interior (lumen) of
membrane-bound
organelles
• Export out of the cell
Cytoplasmic Organelles:
Endoplasmic Reticulum (ER)
• Smooth Endoplasmic
Reticulum (SER)
– No ribosomes
– Functions
• Lipid synthesis
• Ca2+ storage
• Vesicular release
Cytoplasmic Organelles:
Golgi Apparatus
• Stacks of flattened sacs
• Functions:
– processes ER products into
final form
– sort and direct finished
products to final
destinations (intracellular or
extracellular)
– vesicles - small membrane
coated chambers used to
transport materials
Cytoplasmic Organelles:
Lysosome
• Sac-like organelles
which contain enzymes
• Break down large
molecules
– cell’s “digestive system”
• Destroy bacteria, old
organelles, etc.
Cytoplasmic Organelles:
Mitochondria
• Surrounded by two
membranes
• Possess own DNA
• Power generators of the
cell
• Convert food energy (e.g.,
glucose) to usable form
– ATP
• high energy compound.
• major source of metabolic
energy for the cell
The Nucleus
The Nucleus
• Cell's "control center"
• Largest organelle
• Surrounded by
nuclear envelope
• Contains DNA
– genetic information in form
of nucleic acid polymers
– instructs synthesis of
proteins
DNA Structure
• Deoxyribonucleic acid
• Polymer of nucleotides
– base + sugar + phosphate
• Four different bases
– adenine (A), guanine (G),
cytosine (C), thymine (T)
– alternate in order
– “Four-letter alphabet”
• Double helix
– Two strands linked together
by hydrogen bonds
– Complementary sequences
Genes and Chromosomes
• Genes
– sequences of DNA
containing information
needed to make proteins
with the proper amino acid
sequence
• DNA is wrapped around
proteins to form
chromosomes
Chromosomes
• 46 chromosomes per
human cell
• 23 different types
– pairs of homologous
chromosomes
– one of each pair
inherited from each
parent
DNA function
•
Information in DNA used to
make proteins
1. Transcription:
•
sequence of DNA copied into
an RNA (ribonucleic acid)
molecule
2. Translation
•
RNA sequence read by
ribosomes to generate a
protein with a specific amino
acid sequence
Cell Reproduction
• Reproduction of cells (cell division)
requires :
– copying of the DNA (chromosomes)
– distribution of chromosomes to daughter cells
• Two types of cell division
– mitosis (most cells)
– meiosis (gametes)
Mitosis
• Cells duplicate all
their chromosomes
• One copy of each of
the 46 chromosomes
is distributed to each
of the daughter cells.
Meiosis
• Occurs only in gametes
• Cells duplicate all
chromosomes
• Cells undergo two separate
divisions
– each daughter cell has 23 total
chromosomes
• Gametes combine to form a
new cell (zygote) with 46
chromosomes