Cell Theory & Cell Structure

Cell Theory

• All organisms consist of cells.
• The cell is the basic structural and functional unit of all living things.
• Cells arise from the division of pre-existing cells.
• Cells can be cultured in vitro (outside the organism) or in vivo (inside the organism).

Cell Structure and Basic Functions

• Cell components work together to maintain homeostasis and perform life activities.

Cell Membrane

• Surrounds the cell, providing mechanical support and maintaining shape.
• Acts as a selective barrier regulating the passage of substances.
• Plays a crucial role in cellular communication.
• Primarily made of cellulose, a polysaccharide.

Cell Nucleus

• Houses DNA and is located in the center of eukaryotic cells.
• Stores and safeguards genetic information.
• Contains the nucleolus, which is involved in ribosome synthesis.

Cytoplasm

• Gel-like matrix containing water, salts, proteins, and other molecules.
• Site of biochemical reactions, energy production, and substance transport.
• Provides structural support to the cell and is essential for cellular metabolism.

Protein Synthesis

• Protein synthesis is essential for cellular structures, regulating biological processes, and expressing specific characteristics.

Ribosomes

• Organelles essential for cellular functioning and survival.
• Synthesize proteins using genetic information from mRNA.
• Located in the cytoplasm and the rough endoplasmic reticulum.
• Referred to as the "protein factories" of the cell.

Endoplasmic Reticulum (ER)

• A network of interconnected membranes extending from the nuclear membrane to the cell membrane.
• Transports, processes, and distributes proteins and lipids.
• The Rough Endoplasmic Reticulum (RER) contains ribosomes, involved in protein synthesis and modification.
• The Smooth Endoplasmic Reticulum (SER) specializes in lipid synthesis, carbohydrate metabolism, and detoxification.

Golgi Apparatus

• Processes and packages proteins and lipids.
• Synthesizes carbohydrates and lipoproteins.
• Essential for maintaining the cell’s internal balance and facilitating communication.
• Composed of flattened sacs called cisternae.
• Acts as the ‘shipping center’ as it sorts and packages proteins into vesicles for transport.

Mitochondria

• Generate energy through cellular respiration (ATP production).
• The double membrane allows the organization of various stages of the respiratory chain.
• Vital for cellular function and survival.

Chloroplasts

• Carry out photosynthesis, converting solar energy into chemical energy.
• Synthesize glucose and other organic compounds using carbon dioxide and water.
• Responsible for the production of oxygen.

Lysosomes

• Contain digestive enzymes to break down molecules and unwanted cellular materials.
• Facilitate cellular digestion by disposing of waste, recycling nutrients, and defending against pathogenic invasions.

Peroxisomes

• Contain enzymes that degrade hydrogen peroxide and toxic compounds.
• Protect the cell from oxidative damage.
• Play a role in the synthesis and degradation of lipids and bile acids, regulating lipid metabolism and overall homeostasis.

Cytoskeleton

• Composed of protein filaments (microtubules, microfilaments, and intermediate filaments) and provides support and enable movement in eukaryotic cells.
• Encompasses stability, intracellular transport, and contraction.
• Regulates cell shape and plays a role in division, migration, and communication.

Flagella and Cilia

• Specialized structures for movement.
• Flagella are elongated and enable locomotion in liquid environments.
• Cilia are shorter and create a coordinated flow on the cell surface.
• Composed of microtubules in a '9+2' pattern, essential for sperm motility.

Vacuoles

• Membrane-bound organelles found in animal and plant cells.
• Store nutrients, water, ions, and waste materials.
• Regulate turgor pressure and osmotic balance.
• Can be involved in digestion and serve as a defense mechanism containing toxins.

Vesicles and Endosomes

• Membrane vesicles that transport specific materials between organelles and cell membrane.
• Vesicles transport materials from the endoplasmic reticulum and the Golgi apparatus to other destinations.
• Endosomes capture and distribute materials for degradation, recycling, or their incorporation into metabolic pathways.

Cell Cycle

• The sequence of phases in the life cycle of a cell.
• A typical human cell cycle lasts 24 hours.
• G1 phase takes 11 hours.
• S (Synthesis) phase takes 8 hours.
• G2 phase takes 4 hours.
• M (Mitosis) phase takes 1 hour.

Interphase

• Often called the resting phase; the cell is not actively dividing.
• Occupies 23 hours or 95% of the entire cell cycle.
• Subphases include G1, S, and G2.
• During G1, the interval between Mitosis and the beginning of DNA replication, the cell synthesizes proteins important for replicating chromosomes.
• During S, DNA replication starts, chromosomes are replicated, resulting in two identical copies of DNA connected by the centromere called sister chromatids.
• During G2, proteins are synthesized in preparation for mitosis while cell growth continues, and replicated chromosomes condense.

Mitosis

• The cell’s way of making copies of itself.
• Growth, repair, and replacement of old or damaged cells.
• Occurs in somatic cells.

Mitosis: Interphase

• The longest part of the cell cycle.
• The cell grows, replicates DNA, and prepares for cell division.

Mitosis: Prophase

• Chromatin condenses into visible chromosomes.
• Each chromosome consists of two identical sister chromatids joined at the centromere.
• Spindle fibers start forming.

Mitosis: Metaphase

• Chromosomes line up along the center or equator of the cell.
• Spindle fibers are formed.

Mitosis: Anaphase

• Sister chromatids separate.
• Spindle fibers attached to the centromere shorten, pulling the sister chromatids apart to opposite poles.
• Spindle fibers start breaking down.

Mitosis: Telophase

• Separated chromosomes reach the opposite poles of the cell.
• New nuclear envelopes begin to form.
• Chromosomes start to discondense back into chromatids.
• Spindle fibers disassemble.

Cytokinesis

• The cytoplasm divides into two identical daughter cells (diploid cells).
• In animal cells, a cleavage furrow pinches the cell membrane inward until the cell divides.
• A human cell typically has 46 chromosomes or 23 pairs of chromosomes.

Meiosis

• A type of cell division where a single cell divides twice, producing four daughter cells (haploid cells).
• Ensures organisms produced via sexual reproduction contain the correct number of chromosomes, half from each parent.

Meiosis 1: Prophase 1

• Chromosomes condense.
• Crossing over occurs, genetic material is exchanged.

Meiosis 1: Metaphase 1

• Chromosomes align at the center or equator of the cell.
• Random assortment of chromosome pairs occurs.

Meiosis 1: Anaphase 1

• Chromosome pairs separate and move to approach the opposite ends of the cell.

Meiosis 1: Telophase 1

• Two new nuclei form around each set of chromosomes.
• Cytoplasm splits to form two haploid daughter cells.

Meiosis 2: Prophase 2

• Allows four haploid cells (egg/sperm cells) to be formed.
• Chromosomes condense.
• Spindle fibers start to form.

Meiosis 2: Metaphase 2

• Chromosomes align in a single file line in the center/equator of the cell.
• Ensures that sister chromatids separate in the next stage.

Meiosis 2: Anaphase 2

• Sister chromatids separate and move to opposite poles of the cell.

Meiosis 2: Telophase 2

• Four new nuclei form around each set of chromosomes.
• Cytoplasm splits, forming four haploid daughter cells.

Sexual Reproduction

• Involves the union of gametes, or sex cells.
• Fertilization occurs with the egg and sperm cells.

Sexual Reproduction: Internal Fertilization (In Vivo)

• Occurs within the female reproductive tract, sometimes resulting in fertilization of egg cells in the uterus.
• Sperm and egg cells meet at the fallopian tube.
• Copulation refers to sexual intercourse or mating, that occurs in fertilization.

Sexual Reproduction: External Fertilization (In Vitro)

• Happens outside the female reproductive system.
• Requires watery or moist environments to prevent the gametes from drying out.
• Both genders release clusters of gametes in the same area, called spawning.
• Exposure to harsh conditions lessens the survival rate of the zygotes.

Asexual Reproduction

• Does not involve the union of gametes.
• Requires only one parent organism.
• Creates genetically identical offspring.
• Commonly used by unicellular organisms.

Asexual Reproduction: Binary Fission

• The simplest form of asexual reproduction.
• Common in single-cell organisms.
• The genetic material of the parent cell is replicated, followed by division into two identical daughter cells.
• Examples include bacteria, protozoans, archaeans, amoeba, etc.

Asexual Reproduction: Bud Formation

• Common in plants and some cnidaria.
• A new organism develops from an outgrowth (bud) on the parent's body.
• The bud contains actively dividing cells.
• Casts off to become a new being when the source of food in the environment is abundant.
• Examples include hydra and cnidarians.

Asexual Reproduction: Fragmentation

• Each fragment can create new clones that match the genetical information exactly.
• Develops from the whole body that is cut up into fragments.
• Some animals have a self-cutting protection mechanism called autotomy.
• Examples: planaria.

Asexual Reproduction: Regeneration

• The ability to regrow a cut-off part.
• Often takes place in simple organisms.
• Examples include lizards and starfish.

Asexual Reproduction: Spore Formation

• Formation of many spores stored in special structures called sporangium.
• Easily carried by wind, pollinators, and humans.
• Germinates if it lands in a sufficient place.
• Examples include mushrooms, molds, fungi, fern, and moss.

Asexual Reproduction: Parthenogenesis

• An egg cell develops into an embryo without sperm involvement.
• Usually found in facultative or obligate species.
• The cell may be haploid or diploid.
• Examples include ants, wasps, bees, hornets, gumamela, papaya, acorn, etc.

Asexual Reproduction: Vegetative Propagation

• A form of asexual reproduction common in plants.
• Can be artificial or natural.

Natural Propagation

• Runners/Stolons: slender branches with nodes that develop roots and buds and are NOT underground.
• Bulbs: short underground stems with fleshy leaves.
• Tuber: swollen part of an underground stem with pits or eyes.
• Rhizome: long, horizontal, underground stems with nodes or internodes.
• Corm: short, vertical, underground stems with nodes and internodes where buds grow and develop into new plants.

Artificial Propagation

• Cutting: removing a part of the mother plant and potting it in a separate area.
• Layering: shoots or branches are bent down close to the ground and covered with moist soil.
• Grafting: combining two parts from different plants to create a new one.

Force & Motion

• Commonly exerted as a push or a pull applied on an object.
• The result of interaction between objects that can cause changes in motion.
• Examples: door opening, book falling, person walking, etc.

Key Terms: Force & Motion

• Acceleration: how fast an object can move when reaching the point of velocity.
• Magnitude: term for distance or quantity traveled (may be displacement).
• Speed: how fast an object can go, often measured in m/s (meters per second).
• Equilibrium: a state of rest that will not result in a change of motion due to balanced forces.
• Motion: constant change of position in a period of time.
• Velocity: how fast an object is going, accounting for the direction it is going in.

Average Speed

• Describes motion according to the fastness or slowness of an object.
• Disregards direction of motion.

Average Velocity

• Describes motion according to the fastness or slowness of an object plus direction traveled and displacement.
• Focuses more on direction and displacement.