Levels of Organization:
Multi-cellular (many-celled) organisms have the following five levels of organization:
Cells - Tissue - Organs - Organ systems - Organisms
Intro to Cells & Cell Theory:
CELL THEORY
1) all living organisms are made of 1 or more cells
2) a cell is the basic organizational unit of life that can function on its own
3) all cells come from pre-existing cells
Cell Parts and Their Functions
Our bodies are made up of 100 trillion cells
Organelles are small structures in cells that maintain the process of life:
Intake of nutrients (food/water/minerals)
Movement
Growth
Response to stimuli
Exchange of gases
Reproduction
Types of Membranes:
Permeable membranes allow all molecules/particles which can normally move through living cells to pass through the membrane due to large pores
Impermeable membranes - do not allow any particles to pass through due to no pores
Semi-permeable - allows water, carbon dioxide, & oxygen molecules to pass through due to sub-microscopic pores
E.g.. Cell membrane
Diffusion:
Diffusion is the process by which particles move from an area of high concentration to an area of low concentration
The dissolved particles are solutes, and the liquid it is in is called the solution
Osmosis:
Osmosis is the difusion of water accross a semi-permiable membrane
Water moves in the direction of the greater solute concentration
This equalizes the concentrations of materials on either side of the membrane
Structures and Organelles:
Some structures are the same for plant and animal cells
Cell Membrane:
The cell membrane forms a protective barrier around the cell
Made of a double layer of lipids
Materials can diffuse across the cell membrane
PLANT AND ANIMAL CELL PARTS
Cell Membrane (Both): The cell membrane forms a protective barrier around the cell, made of a double layer of lipids. Materials can diffuse across the cell membrane.
Cell Wall (Plant Cells): Found in plant cells, the cell wall provides additional support and protection. It is rigid and composed mainly of cellulose.
Cytoplasm (Both): The cytoplasm is a gel-like substance within the cell membrane that contains organelles and is the site for many cellular processes.
Ribosomes (Both): Ribosomes are the cellular structures responsible for protein synthesis. They can be free-floating in the cytoplasm or attached to the Rough Endoplasmic Reticulum.
Smooth Endoplasmic Reticulum (Both): The SER is involved in lipid synthesis and metabolism, detoxification, and calcium ion storage. It lacks ribosomes on its surface.
Rough Endoplasmic Reticulum (Both): The RER has ribosomes on its surface and is involved in protein synthesis and modification. It also aids in the transport of proteins to the Golgi apparatus.
Golgi Apparatus (Both): The Golgi apparatus modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
Lysosomes (Both): Lysosomes contain enzymes that digest waste materials and cellular debris. They are considered the cleaning crew of the cell.
Mitochondria (Both): Mitochondria are known as the powerhouse of the cell, generating ATP through cellular respiration. They have their own DNA and replicate independently.
Chloroplasts (Plant Cells): Chloroplasts are found in plant cells and are responsible for photosynthesis, converting sunlight into chemical energy. They contain chlorophyll, the pigment that captures light.
Vacuoles (Both, larger in Plant Cells): Vacuoles are storage sacs within cells, used to store nutrients, waste products, or other materials. Plant cells typically have a large central vacuole that maintains turgor pressure.
Centrioles (Animal Cells): Centrioles are cylindrical structures involved in cell division, helping to organize the assembly of the mitotic spindle.
Nucleus (Both): The nucleus is the control center of the cell, housing the cell's genetic material (DNA).
Nuclear Membrane (Both): The nuclear membrane surrounds the nucleus, protecting the genetic material and regulating the passage of materials in and out of the nucleus.
Nucleoplasm (Both): Nucleoplasm is the substance within the nucleus, providing a medium for the genetic material and nucleolus.
Nucleolus (Both): The nucleolus is a structure within the nucleus responsible for producing ribosomes.
CELL CYCLE AND MITOSIS
The Life and Death of Skin Cells:
Every minute we lose 30,000 - 40,000 skin cells
Skin is constantly being created and pushed to the outer surface, where it forms a protective barrier
Genes & DNA:
We know from our discussion of organelles that the nucleus contains chromosomes
In almost every cell, chromosomes come in pairs - one of each pair comes from each parent
Chromosomes are made of a material called deoxyribonucleic acid (DNA), which carries the genetic instructions for the development, functioning, growth, and reproduction of all known living organisms.
A single molecule of DNA is divided into segments called genes
Genes provide instructions for making proteins & help give structure to cells by controlling what proteins are made of and when
The Cell Cycle:
Every hour 100 million cells die and equal amounts are created in your body
The repeated cycle of events in the life of a celll is called the cell cycle
The main goal of the cell cycle is division
During cell division, each cell gets a copy of DNA
Stages of the Cell Cycle:
1) Interphase: The phase where the cell spends most of its life, preparing for division by replicating its DNA and increasing in size.
2) Mitosis: The process where the cell divides its replicated DNA into two identical sets, resulting in two daughter cells.
Growth and Cell Division:
A cell spends 90% of it’s time in interphase
One reason cells divide is because as the become larger, the relationship between surface area to cell size changes
Chromosomes:
As you already learned, a chromosome is a long piece of coiled DNA and proteins
Different specifies have different numbers of chromosomes:
Horses have 64
Hermit crabs have 254
Humans have 46
Chromosomes exist in matching pairs, so humans have 2 sets of 23 for a total of 46
Chromatin in the nucleolus condenses to be visible chromosomes which consist if two identical copies called sister chromatids
Each new cell gets 1 identical set of the two sister chromatids
DNA Replication:
Every parent cell makes a copy of every chromosome before it divides - giving one copy to each of the daughter cells - called DNA replication
During replication, each chromosome is duplicated, although 2 copies remain attached to each other
DNA replication is very precise, so when copying errors occur, they are usually detected and fixed by special '“proof-reading” and repair proteins
Mitosis:
10% of a cell cycle is in mitosis
During this phase, all energy is devoted to cell devision
There are 4 phases from which two identical daughter cells emerge
Prophase
Metaphase
Anaphase
Telophase and Cytokineses
Prophase:
During prophase, chromatin condenses to form chromosomes creating sister chromatids
Sister chromatids are attached together at a centromere
Nuclear envelope disintegrates
Spindle Fibers form to move chromatids
Chromatids are attached to spindle via centromeres
In animal cells centrioles move to each end to act as anchors at the poles (also known as centrosomes)
“pro” - before
Metaphase:
During metaphase, each condensed chromosomes move toward the centre of the cell
The centrioles reach the opposite poles
Held in place by the spindle fibers, which stretch from centriole to centriole
“meta” - middle
Anaphase:
During anaphase, sister chromatids seperate at the centromere and are pulled to opposite ends if the cell towards the centroles
“ana” - away
Telophase:
The last phase is telophase where the cell divides into two new portions
“telos” - end
Spindle fibers start to dissapear
Membranes form around 2 new daughter nuclei
Nuclelus appears and chromosomes become less coiled and harder to see
Rest of the cell is now ready to divide
Cytokinesis:
The process of splitting is called cytokinesis
In animal cells, the cell is halved by the cleavage furrow
In plant cells, the cell is halved by a cell wall which forms internally
Mitosis: The Result
The end product is two identical daughter cells each with the same DNA, size, organelles, and functions
In humans, the chromosomes must double to 92 so that when they are halves, they return to the functioning number of 46 (2 sets of 23)
Mitosis is continuous - there are no breaks between phases
CELL GROWTH AND REPAIR
Various cells undergo mitosis at various rates
The reasons for mitosis are
Growth - as you grow in size, you need more cells, eg: as an adolescent becomes a young adult
Maintenance - some cells have high rates of damage such as stomach ining cells being exposed to HCI
Repair - damage to cells such as injury, ie cuts to your skin
Apoptosis:
Necrosis occurs when cells are exposed to various noxious chemical or are cut off from nutrients & oxygen
Cell death is also regulated and controlled through a process called apoptosis
Apoptosis is programed cell death and is used when cells have lost their ability to perform efficiently or have been invaded by viruses
Cancer Cells:
A cancer cell that divides unconditionally and uncontrollable
When a cell DNA has changed, it is known as a mutation
Viruses, UV radiation, and cigarrette smoke can all cause mutations leading to cancer
Some cancers are inherited
Normal cells live on average 50-60 lifespans, cancer cells do not stop dividings
Cancer cells do not undergp any checkpoints during interphase which would normally terminate the cell
Metastasis:
Cancer spreads to other parts of body
Why is DNA important?:
Each DNA molecule contains 100s or 1000s of genes
DNA controls many features such as your hair, and eye colour of whether you can digest certain foods eg. Diary or Gluten
Through your genes, your DNA also determines how your body might function or look, since genes control what proteins are made
DNA Screening:
Testing for genetic disorders is referred to as genetic screening or DNA screening
Some types of geentic disorders can be observed by looking at a person’s chromosomes
Example of this is Down Syndrome which can even be detected in a fetus
Another example that can be detected through early DNA screening is:
PKU - Which can lead to brain damage if left untreated
Altering Genes: Transgenic Organisms & CLONING:
Genetic code is universal, which means the same 4 DNA building block molecules produce the code for proteins in all types of organisms, including bacteria, plant and animals
For a number of years, scientists have been combining DNA from different species through genetic engineers
These “altered” species are called transgenic organisms (or genetically modified organisms, GMO)
Closing is the process of producing identical offspring from genes, cells, or an entire organism
Eg. Taking cuttings from a plant, rooting them and producing more plants that are the exact copies of the parent plant