Biology: Cell Theory, Organelles, DNA, Cell Cycle, and Systems

Cell Theory

All living organisms are made of one or more cells. The cell is the basic organizational unit of life. All cells come from pre-existing cells.

Organelles

Small parts within a cell that perform certain tasks.

Cell Wall

Provides support for plant cells.

Cell Membrane

Surrounds, protects, and controls flow of material into and out of the cell.

Cytoplasm/Cytosol

Fluid that holds all organelles.

Golgi Apparatus

Sorts and packages proteins.

Mitochondria

Produce energy for cellular activities.

Chloroplast

Converts energy from the Sun into stored energy for the cell (photosynthesis).

Lysosome

Breaks down and recycles old organelles.

Nucleus

Controls all cellular activities.

Nucleolus

Contains information (RNA) for producing ribosomes.

Nuclear Membrane/Nuclear Envelope

Protects DNA within the nucleus.

Nuclear Pores

Openings within the nuclear membrane.

Chromatin/Chromosomes

Contains condensed genetic material (DNA).

Ribosomes

Produce proteins.

Endoplasmic Reticulum

Transport materials.

Cytoskeleton

Framework for the cell to maintain structure.

Centrioles

Involved in cell division.

Cilia and Flagella

Enable cell movement; Cilia = wave-like motion, Flagella = whip-like motion.

Vacuole

Store materials.

DNA

Deoxyribonucleic acid; found in chromosomes inside the nucleus.

Nucleotide

Subunit (1 molecule of DNA).

Genes

Segments of DNA that control protein production.

Discovery of DNA

In 1953, scientists James Watson and Francis Crick created the double helix model of DNA.

DNA Structure - Double Helix

DNA has two main parts: the sugar-phosphate backbone and the nitrogen bases.

Importance of DNA

Controls many features through the production of proteins.

DNA Screening

Analyzing a karyotype may allow doctors to detect potential genetic disorders.

Genetic Disorders

Caused by abnormalities in a person's DNA.

Mutations

A change in the DNA of an organism, may be caused by mutagens.

Cell Cycle

A continuous sequence of cell growth and division.

DNA Replication

Takes place during interphase of the cell cycle.

Stages of Mitosis

Prophase, Metaphase, Anaphase, Telophase.

Cytokinesis

The division of the rest of the cell (Cytoplasm and other organelles)

Prophase

Nuclear membrane breaks down, centrioles move to opposite poles, spindle fibres appear, nucleolus disappears

Metaphase

Centrioles reach opposite poles, chromosomes line up in the middle of the cell, spindle fibres attach to centromeres

Anaphase

Spindle fibres pull double-stranded chromosomes apart towards the poles; each single-stranded chromosome is called a chromatid

Telophase

Chromatids reach opposite poles, spindle fibres disappear, nuclear membrane reappears, nucleolus reappears

Cytokinesis in Animal Cells

Cell membrane 'pinches in' until 2 cells are created

Cytokinesis in Plant Cells

Golgi bodies produce vesicles that line up between the 2 new cells, creating a cell plate in the middle

End Result of Mitosis

Two identical cells containing the same genetic information (same number of chromosomes)

Cell Cycle Checkpoints

Specialized proteins that manage the cell cycle and ensure cell division does not occur if conditions are not met

Consequences of Not Dividing

Many cells become non-dividing (e.g., muscle, nerve cells) or undergo pre-programmed cell death (apoptosis)

Cancer

Cells with abnormal genetic material that are dividing uncontrollably and can spread to other body parts

Unusual Features of Cancer Cells

They cannot stop dividing, do not obey signals from other cells, do not self-destruct when damaged, and do not stick together

Types of Tumours

Benign: slow-growing/non-growing tumour that does not spread; Malignant: fast-growing tumour that can spread throughout the body

Metastasis

When cancer cells escape to a new part of the body and may start new tumours

Causes of Cancer

DNA damage through mutations, especially in regions that produce checkpoint or 'suicide' proteins

Carcinogens

Things that cause DNA mutations, including tobacco, toxins, radiation, and some viruses

Prevention of Cancer

Avoid carcinogens

Early Diagnosis of Cancer

Annual health checks

Treatment of Cancer

Surgery, radiation therapy, chemotherapy

Cellular Differentiation

Process where unspecialized cells change shape, contents, and structure to perform different functions

Stem Cells in Animals

Unspecialized cells that can differentiate into various cells in the body

Types of Stem Cells

Embryonic Stem Cells: found in embryos; Adult Stem Cells: found in bone marrow with less flexibility of specialization

Plasticity of Stem Cells

Ability to turn into different tissues; early in development, they are totipotent, then pluripotent, and finally adult stem cells

Applications of Stem Cells

Medical treatments to repair and replace damaged cells in patients

Controversies in Stem Cell Research

Ethical/moral/legal issues regarding cloning human embryos and the destruction of embryos for stem cells

Factors Influencing Cell Specialization

Effect of cytoplasm, environmental conditions, and neighboring cells

Effect of Cytoplasm

Cytokinesis can lead to uneven distribution of organelles and contents in daughter cells

Effect of Environmental Conditions

Triggers for specialization can include temperature and presence/absence of nutrients

Effect of Neighboring Cells

Substances produced by one cell can diffuse through a neighboring cell's membrane and change gene expression

Diffusion

Movement of particles from an area of high concentration to low concentration without using energy

Ingestion

Intake of food

Egestion

Excretes as solid waste feces

Digestive Tract

Includes mouth, esophagus, small intestine, stomach, and large intestine

Accessory organs

Includes liver, gallbladder, and pancreas

Small Intestines

Covered with millions of inner folds, called microvilli and villi

Microvilli and Villi

Increase surface area for absorption of nutrients in the small intestines

Muscular and Skeletal Systems

Involved in body movement

Digestive and Circulatory Systems

Break down food and dissolve nutrients in blood to transport to cells

Circulatory and Respiratory Systems

Transport oxygen to all cells in the body for cellular respiration

X-Rays

A beam of high-energy electromagnetic radiation transmitted through the body onto photographic film

X-Rays Pros

Best used for hard tissue (e.g., bones) since x-rays go through soft tissues

X-Rays Cons

Exposure to radiation

CT (CAT) Scan

X-ray source rotates around the body and takes images of thin 'slices' of body part

CT (CAT) Scan Pros

Shows 3-D image and soft tissue more clearly than x-ray

CT (CAT) Scan Cons

Exposure to radiation

Ultrasound

A small transmitter sends a high-frequency sound wave reflected by internal structures

Ultrasound Pros

No adverse effects reported; can monitor real-time movement of body parts

Ultrasound Cons

Do not produce clear images

MRI

Magnetic Resonance Imaging that surrounds the body with a strong magnetic field

MRI Pros

Very clear image; excellent for viewing soft tissues; no exposure to radiation

MRI Cons

Expensive; time-consuming; claustrophobia

Endoscopy

A tiny camera and light attached to a flexible tube inserted into body opening

Endoscopy Pros

Good for detecting ulcers in stomach or intestine

Endoscopy Cons

May tear tissue walls; risk of infection, bleeding, and pain

Tissue

A cluster of similar cells that share the same specialized structure and function

Xylem

Tissue that transports water and minerals in one direction (roots → stems → leaves)

Phloem

Tissue that transports sugars made in leaves in two directions (leaves ↔ roots, stems, fruits)

Organ

A combination of several types of tissue working together to perform a specific function.

Epithelial Tissue

Cells tightly packed, minimal extracellular space, arranged in sheets, forming coverings and linings.

Connective Tissue

Cells widely spaced in an extracellular matrix, functions include support, protection, and transport.

Muscle Tissue

Long, contractile cells with actin and myosin, types include skeletal, cardiac, and smooth.

Nervous Tissue

Neurons specialized for signal transmission with long extensions for rapid communication.

Dermal Tissue

Outer layer of plant that protects and reduces water loss.

Ground Tissue

Bulk of plant tissue responsible for photosynthesis, storage, and support.

Vascular Tissue

Transport system in plants that includes xylem and phloem.

Integumentary System

Protection and temperature control.

Skeletal System

Support, protection, and blood cell production.

Muscular System

Movement and heat production.