Biology Midterm Notes
Characteristics of Living Things
1. Organisms tend to be complex and highly organized.
2. Living organisms have the ability to take energy from the environment and
change it from one form to another.
3. Organismstendtobehomeostatic– they regulate their bodies and other internal
structures to certain
4. Living creatures respond to stimuli. normal parameters.
5. Living things reproduce themselves by making copies of themselves.
6. Organisms tend to grow and develop.
7. Life adapts and evolves in step with external changes in the environment.
Lecture 2: A tour of the Cell
Anthony van Leeuwenhoek
Single Lens - ca. 1673
The Cell: first person to coin the word 'cell' to describe the tiniest
components of living systems - plants!
1635 - 1703
The Electron Microscope
Resolution limit of Light Microscope is about 0.2 microns (size of a small
bacterium – remember 1 micron is .001mm)
Magnification limit of about 1000 times
In 1950’s the introduction of the electron microscope enabled organelles,
viruses, proteins, etc.. to be imaged
The minimum resolution of a light microscope is about .2 microns, the size of
a small bacterium
Light microscopes can magnify effectively to about 1,000 times the size of the
– At higher magnifications, the image blurs.
Take cells apart to study their components
Centrifuge is used to fractionate cells and separate their major organelles
Ultracentrifuges are capable of speeds as fast as 150,000 rpm applying forces
over 1 million times the force of gravity
Cell = simplest collection of matter which has all the properties of life
1. Lowesthierarchicallevelwhichis alive 2. Cellisbasicunitoflife
3. Cell performs all functions necessary to live and reproduce
Occur in virtually every kind of organism
Some wreck havoc others cause no disease or outward sign of their presence
Often highly specific to host
Can reproduce only when they enter a cell
Pro-beforeandkaryote-nucleus – Examples – bacteria, cyanobacteria,
Nonucleus (genetic information in area
• Visible components–plasma membrane, ribosomes, nucleoid, cytoplasm, cell wall,
pili, flagella, mesosomes, photosynthetic membranes
• Eu - true, karyote - nucleus • Found in four (?) Kingdoms
• True Nucleus (surrounded with nuclear membrane, contains DNA,
• Visible Components
– Plasma membrane, cytoplasm, nucleus, ribosomes, organelles, endomembrane
system, cytoskeleton, cell wall, cell matrix, some organelles, flagella
The nucleus Eukaryotic cell’s genetic library
Most of the genes in a eukaryotic cell.
– Some genes are located in mitochondria and
Averages about 5 microns in diameter.
Separated from the cytoplasm by a double
– These are separated by 20-40 nm.
Where the double membranes are fused, a pore allows large macromolecules
and particles to pass through.
The nuclear side of the envelope is lined by the nuclear lamina, a network of
intermediate filaments that maintain the shape of the nucleus.
Within the nucleus, the DNA and associated proteins are organized into
fibrous material, chromatin.
Appear as diffuse mass. However when the cell
prepares to divide, the chromatin fibers coil up to be seen as separate
Eacheukaryoticspecieshas a characteristic number of chromosomes.
Inthenucleusisaregionof densely stained fibers and granules adjoining
chromatin, the nucleolus.
– In the nucleolus, ribosomal RNA (rRNA) is synthesized and assembled with
proteins from the cytoplasm to form ribosomal subunits.
• Thenucleusdirectsprotein synthesis by synthesizing messenger RNA
Material between the plasma membrane (cell membrane) and the nuclear
Has a variable viscosity
Main chemical constituents are water (approx. 80%), nucleic acids, proteins,
lipids, carbohydrates, pigments, etc.....
• Ribosomes contain rRNA and protein.
• A ribosome is composed of two subunits that combine to carry out protein
Cell types that synthesize large quantities of proteins (e.g., pancreas) have
large numbers of ribosomes and prominent nuclei.
• free ribosomes, are suspended in the cytosol and synthesize proteins that
function within the cytosol.
• bound ribosomes, are attached to the outside of the endoplasmic reticulum.
• Ribosomes can shift between roles
Many of the internal membranes in a eukaryotic cell are part of the
These membranes are either in direct contact or connected via transfer of
vesicles, sacs of membrane.
The endomembrane system includes the nuclear envelope, endoplasmic
reticulum, Golgi apparatus, lysosomes, vacuoles, and the plasma
There are two regions of ER that differ in structure and function.
– Smooth ER looks smooth because it lacks ribosomes.
– Rough ER looks rough because ribosomes (bound ribosomes) are attached to the
outside, including the outside of the nuclear envelope. Smooth ER
Smooth ER is rich in enzymes and plays a role in a variety of metabolic
Synthesize lipids, including oils, phospholipids, and steroids.
Smooth ER also catalyzes a key step in the mobilization of glucose from
stored glycogen in the liver.
Other enzymes in the smooth ER of the liver help detoxify drugs and poisons.
– These include alcohol and barbiturates.
– Frequent exposure leads to proliferation of smooth ER, increasing
tolerance to the target and other drugs.
Muscle cells are rich in enzymes that pump calcium ions from the cytosol to
Rough ER is especially abundant in those cells that secrete proteins.
– As a polypeptide is synthesized by the ribosome, it is threaded into the
cisternal space through a pore formed by a protein in the ER membrane.
Secretory proteins are packaged in transport vesicles that carry them to their
• Rough ER is also a membrane factory.
– Membrane bound proteins are synthesized directly into the membrane.
– Enzymes in the rough ER also synthesize phospholipids from precursors in
– As the ER membrane expands, parts can be transferred as transport
vesicles to other components of the endomembrane system.
Lecture 3: Tour of the Cell 2
The Golgi Apparatus
• transport vesicles from the ER Golgi apparatus for modification of their
• center of manufacturing, warehousing, sorting, and shipping
• extensive in cells specialized for secretion.
The Golgi Apparatus
• flattened membranous sacs – cisternae
– looking like a sac of pita bread
• membrane of each cisterna separates
its internal space from the cytosol • cis side -- receives material by fusing with vesicles, while the other side, the trans
side, buds off vesicles that travel to other sites
During their transit from the cis to trans pole, products from the ER are
modified to reach their final state
can manufacture its own macromolecules, including pectin and other non-
tags, sorts, and packages materials into transport vesicles
• The lysosome is a membrane-bounded sac of hydrolytic enzymes that
Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and
These enzymes work best at pH 5.
– Proteins in the lysosomal membrane pump hydrogen ions from the cytosol
to the lumen of the lysosomes.
Rupturing one or a few lysosomes has little impact on a cell
– Massive leakage from lysosomes can destroy an cell - autodigestion.
Lysosomes can fuse with food vacuoles, formed when a food item is brought
into the cell by phagocytosis.
Lysosomes can also fuse with another organelle or part of the cytosol.
– This recycling, this process of autophagy renews the cell.
• Vesicles (or Microbodies) and vacuoles (larger versions) are membrane-bound
sacs with varied functions.
– Food vacuoles, from phagocytosis, fuse with lysosomes.
– Contractile vacuoles, found in freshwater protists, pump excess water out of the
– Central vacuoles are found in many mature plant cells.
Plant Central Vacuole
The membrane surrounding the central vacuole, the tonoplast, is selective in
its transport of solutes into the central vacuole.
Functions - stockpiling proteins or inorganic ions, depositing metabolic
byproducts, storing pigments, and storing defensive compounds against
Endomembrane system plays a key role in the synthesis (and hydrolysis) of
macromolecules in the cell.
• The various components modify macromolecules for their various functions.
Mitochondria and Chloroplasts
Cell Energy Transformers Mitochondria and chloroplasts - main
energy transformers of cells
• Mitochondria and chloroplasts are the organelles that convert energy to forms
that cells can use for work.
• Mitochondriaarethesitesofcellularrespiration, generating ATP from the
catabolism of sugars, fats, and other fuels in the presence of oxygen.
• Chloroplasts, found in plants and eukaryotic algae, are the site of photosynthesis.
Like mitochondria, chloroplasts are dynamic structures.
– Their shape is plastic and they can reproduce themselves by pinching in
Mitochondria and chloroplasts are mobile and move around the cell along
tracks in the cytoskeleton.
Found in Plant and Animal cells
Enzymesthattransferhydrogenfrom various substrates to oxygen
Thisproduceshydrogenperoxidewhich is then converted to water
• Are made from cytosol not endomembrane system??
• The cytoskeleton is a network of fibers extending
throughout the cytoplasm.
• Thecytoskeleton organizes the structures and activities of
Structural support - cell motility -
• mechanical support and maintains shape of the cell
• Fibers act like a geodesic dome to stabilize a balance between opposing forces.
anchorage for many organelles and cytosolic enzymes.
Dynamic - dismantling in one part and reassembling in another to change cell
shape. Property Microtubules Mifrofilaments Intermediate
Two intertwined Fibrous proteins
Structure Hollow tubes
strands super coiled
Diameter 25 nm 7 nm 8 – 12 nm
Protein Tubulin Actin Keratin proteins
Maintain cell shape
Cell motility Maintain cell shape
Change cell shape Maintain cell
Function Chromosome Muscle contraction shape Organelle
Organelle Cytoplasmic streaming anchorage
• Hollow tubes
• 25 nm diameter
• Composed of protein tubulin
• Cell shape, cell mobility, chromosome movement, organelle movement
Anotherfunctionis as tracks that guide motor proteins carrying organelles to their
Two intertwined actin strands
7 nm in diameter
Cell shape, muscle contraction, cytoplasmic streaming, cell motility, cell
• Thick cables
• Different proteins (keratin family)
• Anchorage of nucleus and organelles
Centrosomes and Centrioles
In many cells microtubules grow out of the centrosome (region locate near
Within centrosome of animal cell are a pair of centrioles (9 sets of triplet
microtubules arranged in a ring
– Not present in plant cells Centrosome
In animal cells, the centrosome has a pair of centrioles, each with nine
triplets of microtubules arranged in a ring.
During cell division the centrioles
• Cilia - large numbers on the cell surface.
– They are about 0.25 microns in diameter and 2-20 microns long.
• One or a few flagella per cell.
– Flagella are the same width as cilia, but 10-200 microns long.
• A flagellum has an undulatory movement.
– Force is generated parallel to the flagellum’s axis.
• The bending of cilia and flagella is driven by the arms of a motor protein, dynein.
– ATP supplies energy
– Dynein arms alternately
grab, move, and release
the outer microtubules.
– Protein cross-links limit sliding and the force is
expressed as bending.
Cilia and flagella have the same ultrastructure.
Core of microtubules sheathed by the plasma membrane.
Nine doublets of microtubules arranged around a pair at the center, the “9 +
Flexible “wheels” of proteins connect outer doublets to each other and to the
Outer doublets are also connected by motor proteins.
Anchored in the cell by a basal body (centriole)
Thousands of actin filaments are arranged parallel to one another.
Thicker filaments composed of a motor protein, myosin, interdigitate with
the thinner actin fibers.
Myosin molecules walk along the actin filament, pulling stacks of actin fibers
together and shortening
• In plant cells (and others), actin- myosin interactions and sol-gel transformations
drive cytoplasmic streaming. Plant Cell Wall
Much thicker than plasma membrane
pm 0.008 microns (not visible in LM)
Cell wall 0.1 to several microns thick (visible in LM)
Cell walls are strong
Composition – fibres of cellulose (polymer of glucan), embedded in other
polysaccharides also pectin (polysaccharide)
• Anchoring Junctions (Desmosomes)
– Fig. 7.30
– Two cells attached by intercellular filaments – rivet cells together
• Tight Junctions
– Prevent materials from moving between cells – Form a belt around cell – forms a
• Gap Junctions
– Intercellular connections between animal cells
– Like Plasmodesmata, small molecules can pass
Lecture 4: Divide and Conquer
What do all cells require to survive?
•A complete set of genetic instructions
• Produce required molecules • direct life processes
• Genetic instructions are coded in the DNA of cells
Why do cells divide?
Activities of a cell from one cell division to the next
Cell divides into two identical daughter
Essential Features of Cell Division
Transmit a complete copy of genetic information (DNA)
Transmit materials necessary for cell to survive and use genetic information
Prokaryotic Cell • no nucleus – genetic material (DNA) in cytoplasm
• no membrane-bound organelles
• example: bacteria
• cell division is called binary fission
Prokaryotic Cell Cycle
Prokaryotic chromosome a circular loop
chromosome attaches to one point on plasma membrane
chromosome is replicated
– replicated chromosome attached to plasma membrane at a different nearby
Prokaryotic Cell Cycle
cellelongates–new plasma membrane is added between between chromosomes,
pushing them towards opposite ends of cell
plasma membrane grows in ward at middle of cell
parent cell is divided into two identical daughter cells
membrane-bound organelles, including a nucleus
genetic material (DNA) contained within the nucleus
examples: fungi, protists, plants, animals
• cell division of somatic cells called mitotic cell division
• Contain almost all the genetic information
– Mitosis only deals with nuclear chromosomes
• Mitochondria and Chloroplasts also have some DNA
– DNA replication here is handled differently
• Chromosomes = long thread like structures
– Highly condensed during Mitosis
– DNA + protein
– Contain most of the organisms genetic information
– # varies with species
Eukaryotic Chromosome Structure
• Strands of linear DNA • Human cells
– 46 strands (46 chromosomes) – Average length 4 cm
Each strand coiled up
Human cell approx. 3 metres of DNA
Total length of DNA in an adult human
approx. 2 x 1013 metres (distance earth to sun and back) Chromatin
• Many proteins are bound to DNA – Protect
– Transcription – Regulation
• DNA + bound protein = chromatin – Chromatin only about 50 % DNA
Review the basics of nucleotides and nucleic acids in the text book.
F37 – F39
You are responsible for this material.
During non-division phase of cell cycle
• DNA molecules in extended, uncondensed form = chromatin
• cell can only use DNA to produce molecules when in extended state
During division phase of cell cycle
DNA molecules condense to form chromosomes prior to division
eachchromosomeisasinglemolecule of DNA
easier to sort and organize DNA into daughter cells
What is Mitotic Cell Division?
Division of somatic cells (non reproductive cells) in eukaryotic
A single cell divides into two identical daughter cells (cellular
• Organisms have a specific number of sets in diploid and haploid cells
• Mitosis and Meiosis lead to different ploidy outcomes
Chromosome ploidy of cell
Ploidy – refers to the number of pairs of chromosomes in cells
• haploid–onecopyofeach chromosome
– designated as “n”
– designated as “2n”
• Haploid = 1 set (n)
• Diploid = 2 sets (2n) • Triploid = 3 sets (3n)
• Polyploid = more than two complete sets
– Common in plants, not animals Eukaryotic Cell Cycle • 2 major phases:
• Interphase (3 stages)
– DNA uncondensed (=
• Mitotic cell division (5 stages)
– DNA condensed (= chromosomes)
G1 – First Gap
Size Increases, Organelles may replicate
Normal Growth and Development
S – DNA synthesis
DNA is replicated, synthesis of
proteins associated with DNA
ploidy does not change
G2 – Second Gap
cell prepares for division, synthesis
of proteins associated with Mitosis
cell committed to divide
Occurs before stages of mitosis
Genetic material is called Chromatin
DNA replication occurs during this phase
•Nucleus well defined •Nucleoli present
•Centrosomes replicated (replicated centrioles in animal cells only)
•Microtubules extend from centrosomes (called aster [star])
•Chromosomes have duplicated but not condensed
Mitosis in Eukaryotic Cells has five stages:
5. Telophase (cytokinesis also occurs during this phase)
•Chromatin fibres become tightly coiled chromosomes •Nucleoli disappear
•Mitotic spindle begins to form
•Centrosomes move away from each other
•Nuclear envelope fragments
•Microtubules connect to chromosomes
•Kinetochores have formed
•Some microtubules connect with those from the opposite pole
•Centrosomes now at opposite poles
•Chromosomes at metaphase plate
•Centromeres of the chromosomes are on the metaphase plate
•Kinetochores of each chromatid connected to microtubules from different pole
•Begins when paired centromeres separate
•Chromosomes (1/2 of each s