Anatomy & Physiology | University of Florida
Difficulty: Introductory to Intermediate | Prerequisites: Cell structure basics (Doc 1) and chemical bonds/metabolism (Doc 2) will help considerably.
This set of topics moves from the molecular level to the tissue and systems level. You will learn how genetic information flows from DNA to protein (the central dogma), how cells organise into the four tissue types, how cells grow and divide, and how the body maintains stability through feedback loops. These concepts bridge the gap between cell biology and organ-system physiology. If you are behind, read the cell structure notes first, because gene expression and the cell cycle both depend on understanding organelles.
DNA stores genetic instructions; transcription copies them into mRNA; translation reads that mRNA to build proteins. Cells with the same DNA specialise into four tissue types (connective, epithelial, muscle, nervous) through differentiation. The cell cycle controls when cells grow and divide. Homeostasis keeps the internal environment stable using feedback loops, predominantly negative feedback.
DNA (deoxyribonucleic acid)
The double-stranded molecule that carries the cell's genetic blueprint. Stored in the nucleus, organised into chromosomes. Think of it as the master instruction manual.
RNA (ribonucleic acid)
A single-stranded nucleic acid involved in executing genetic instructions. Comes in several forms: mRNA, tRNA, rRNA.
mRNA (messenger RNA)
A transcript of a gene, copied from DNA during transcription. Carries the code from the nucleus to the ribosome. In simple terms, it is the photocopy of the recipe that gets taken to the kitchen.
tRNA (transfer RNA)
A small RNA molecule that delivers the correct amino acid to the ribosome during translation. Each tRNA has an anticodon that matches a specific mRNA codon.
rRNA (ribosomal RNA)
The structural and catalytic RNA component of ribosomes. Makes up most of the ribosome's mass.
Transcription
The process of copying a gene's DNA sequence into mRNA, carried out in the nucleus by RNA polymerase.
Translation
The process of reading mRNA at the ribosome to assemble a chain of amino acids into a protein.
Nucleotide
The monomer (building block) of nucleic acids. Each nucleotide consists of a sugar, a phosphate group, and a nitrogenous base.
Nitrogenous bases
The information-carrying part of each nucleotide. DNA uses adenine (A), thymine (T), cytosine (C), guanine (G). RNA replaces thymine with uracil (U). Base pairing: A-T (or A-U in RNA), C-G.
Connective tissue
The most abundant and varied tissue type. Supports, binds, and protects other tissues. Includes bone, cartilage, blood, adipose (fat), and loose/dense connective tissue.
Epithelial tissue
Sheets of tightly packed cells covering body surfaces and lining cavities. Functions include protection, absorption, secretion, and filtration.
Muscle tissue
Tissue specialised for contraction and movement. Three types: skeletal (voluntary), cardiac (heart), and smooth (organs, blood vessels).
Nervous tissue
Tissue that generates and conducts electrical impulses. Made up of neurons (signal carriers) and neuroglia (support cells).
Cell cycle
The ordered sequence of events from one cell division to the next. Includes interphase (growth and DNA replication) and the mitotic phase (division).
Interphase
The longest phase of the cell cycle, during which the cell grows, carries out normal functions, and replicates its DNA in preparation for division. Divided into G1, S, and G2 sub-phases.
Mitosis
Division of the nucleus into two genetically identical daughter nuclei. Proceeds through prophase, metaphase, anaphase, and telophase.
Cytokinesis
Division of the cytoplasm, physically splitting one cell into two. Overlaps with the final stage of mitosis.
Differentiation
The process by which a less specialised cell becomes a more specialised cell type (e.g. a stem cell becoming a neuron). All differentiated cells contain the same DNA but express different genes.
Apoptosis
Programmed cell death. A controlled, orderly process that removes damaged, infected, or unnecessary cells without triggering inflammation. Think of it as a planned demolition rather than an explosion.
Homeostasis
The maintenance of a stable internal environment (temperature, pH, blood glucose, fluid balance) despite changes outside the body.
Negative feedback
A feedback loop in which the response opposes the original stimulus, bringing the system back toward a set point. The most common type of feedback in the body. Example: blood glucose regulation by insulin and glucagon.
Positive feedback
A feedback loop in which the response amplifies the original stimulus, pushing the system further from its starting point until an endpoint is reached. Example: blood clotting, oxytocin during childbirth.
Receptor
A structure (often a protein) that detects a change in the internal or external environment (the stimulus).
Control centre
The structure (often in the brain or an endocrine gland) that receives information from receptors, compares it to a set point, and determines the appropriate response.
Effector
The organ or tissue that carries out the response directed by the control centre (e.g. a muscle contracts, a gland secretes a hormone).
Double helix: two antiparallel strands of nucleotides wound around each other
Each nucleotide = deoxyribose sugar + phosphate group + one of four nitrogenous bases
Base pairing rules: adenine (A) pairs with thymine (T), cytosine (C) pairs with guanine (G)
The sequence of bases along a strand encodes genetic information
Single-stranded; uses ribose sugar instead of deoxyribose; uracil (U) replaces thymine
mRNA: carries the gene's code from nucleus to ribosome
tRNA: ferries amino acids to the ribosome, matching each codon with the correct amino acid via its anticodon
rRNA: structural and catalytic backbone of the ribosome itself
Occurs in the nucleus
RNA polymerase binds to a promoter region on the DNA
The enzyme unwinds the double helix and reads the template strand (3' to 5'), building a complementary mRNA strand (5' to 3')
In eukaryotes, the mRNA is processed (introns removed, exons spliced together, a 5' cap and poly-A tail added) before leaving the nucleus
Occurs at ribosomes in the cytoplasm (or on the rough ER)
The ribosome reads the mRNA three bases at a time (each triplet = a codon)
Each codon specifies one amino acid; tRNA delivers that amino acid
The ribosome links amino acids together by peptide bonds, forming a polypeptide chain
Translation stops when a stop codon (UAA, UAG, UGA) is reached
The polypeptide then folds into its functional 3D shape (often with help from chaperone proteins)
Understanding transcription and translation is the basis for modern medicine and biotechnology. mRNA vaccines (such as those developed for COVID-19) work by delivering synthetic mRNA into cells, which then translate it into a viral protein that trains the immune system.
Connective tissue: the most diverse type. Subtypes include bone, cartilage, blood, adipose (fat), and fibrous connective tissue. All share a common feature: cells are dispersed within an extracellular matrix (ground substance + fibres). Functions: support, protection, binding, transport (blood), energy storage (adipose)
Epithelial tissue: tightly packed sheets of cells with minimal extracellular matrix. Lines body surfaces (skin) and cavities (digestive tract, blood vessels). Functions: protection, absorption, secretion, filtration. Classified by shape (squamous, cuboidal, columnar) and layers (simple = one layer, stratified = multiple layers)
Muscle tissue: specialised for contraction. Three types:
Skeletal: striated, voluntary, attached to bones
Cardiac: striated, involuntary, found only in the heart, cells connected by intercalated discs
Smooth: non-striated, involuntary, found in walls of hollow organs and blood vessels
Nervous tissue: neurons generate and transmit electrical signals; neuroglia (glial cells) support, insulate, and protect neurons. Found in the brain, spinal cord, and peripheral nerves
Cells of the same type group into tissues
Tissues combine to form organs (e.g. the heart contains cardiac muscle, connective tissue, epithelium, and nervous tissue)
Organs work together in organ systems (e.g. cardiovascular system = heart + blood vessels + blood)
Organ systems cooperate to sustain the organism
G1 phase (Gap 1): the cell grows, produces proteins and organelles, carries out normal functions. Longest sub-phase for most cells
S phase (Synthesis): DNA is replicated. Each chromosome is duplicated into two sister chromatids joined at the centromere
G2 phase (Gap 2): the cell checks for DNA replication errors and prepares for mitosis (produces proteins needed for division)
Prophase: chromatin condenses into visible chromosomes; the nuclear envelope begins to break down; spindle fibres form
Metaphase: chromosomes line up along the cell's equator (metaphase plate); spindle fibres attach to centromeres
Anaphase: sister chromatids are pulled apart to opposite poles of the cell
Telophase: nuclear envelopes re-form around each set of chromosomes; chromosomes decondense
Overlaps with telophase
In animal cells, a cleavage furrow pinches the cell in two
Result: two genetically identical daughter cells, each with a full set of chromosomes
All cells in an organism contain the same DNA, but different genes are switched on or off depending on cell type
A stem cell differentiating into a neuron expresses different genes from one differentiating into a muscle cell
Once fully differentiated, most cells do not divide (neurons, cardiac muscle cells); others retain the ability (epithelial cells, liver cells)
A tidy, controlled process: the cell shrinks, its DNA is fragmented, and it is consumed by neighbouring cells or immune cells
Removes cells that are damaged, infected, or no longer needed (e.g. webbing between fingers during embryonic development)
Distinct from necrosis, which is uncontrolled cell death due to injury, and which triggers inflammation
Every homeostatic mechanism follows the same three-component pattern:
Receptor: detects a change (stimulus) in the environment, e.g. thermoreceptors in the skin detect a drop in temperature
Control centre: receives the signal, compares it to a set point, and sends instructions. Often the hypothalamus or an endocrine gland
Effector: carries out the response, e.g. skeletal muscles shiver to generate heat
The response opposes the original stimulus, pushing the variable back toward the set point
Example, blood glucose regulation:
Blood glucose rises after a meal
Pancreas (control centre) detects the rise and releases insulin
Insulin signals cells to take up glucose, liver to store glucose as glycogen
Blood glucose falls back to normal
When glucose drops below the set point, glucagon is released to raise it again
Other examples: body temperature regulation, blood pressure regulation, blood calcium regulation
The response amplifies the original stimulus, driving the system further from its starting point until an event completes the cycle
Example, childbirth:
Pressure of the baby's head on the cervix stimulates nerve impulses to the hypothalamus
The hypothalamus signals the pituitary to release oxytocin
Oxytocin increases uterine contractions, which increase pressure on the cervix, which triggers more oxytocin
The loop ends when the baby is delivered
Other examples: blood clotting cascade, lactation (suckling stimulates more prolactin)
Type 1 diabetes is a failure of negative feedback: the immune system destroys insulin-producing beta cells, so the body cannot lower blood glucose after meals. Understanding the feedback loop explains both the disease mechanism and the rationale for insulin therapy.
Students often think RNA is just a "copy" of DNA with no other role. In fact, RNA comes in several functional forms (mRNA, tRNA, rRNA), and some RNA molecules have catalytic activity (ribozymes).
Mitosis and the cell cycle are sometimes treated as synonyms. Mitosis is only the nuclear-division phase; the cell cycle also includes interphase (G1, S, G2) and cytokinesis.
Positive feedback is sometimes assumed to be beneficial and negative feedback harmful, because of how "positive" and "negative" sound in everyday language. In physiology, negative feedback is the stabilising mechanism responsible for most regulation, while positive feedback drives events to completion and then stops.
Students may think differentiated cells lose DNA. They do not. Every cell retains a full genome; differentiation is about which genes are expressed, not which genes are present.
⚠️ Be able to trace the flow of genetic information: DNA to mRNA (transcription) to protein (translation)
⚠️ Know the base pairing rules for DNA (A-T, C-G) and RNA (A-U, C-G)
⚠️ Identify the four tissue types, their subtypes, and where each is found
⚠️ List the phases of the cell cycle in order, including the sub-phases of interphase and the stages of mitosis
⚠️ Compare negative and positive feedback with named examples of each
⚠️ Explain the three components of a feedback loop (receptor, control centre, effector) using a specific example
True or False: Uracil replaces thymine in RNA. (True)
Fill in the blank: The four stages of mitosis in order are ___, ___, ___, ___. (Prophase, metaphase, anaphase, telophase)
True or False: Positive feedback is the most common feedback mechanism in the body. (False, negative feedback is.)
Fill in the blank: The four primary tissue types are ___, ___, ___, ___. (Connective, epithelial, muscle, nervous)
True or False: Apoptosis triggers an inflammatory response. (False, that is necrosis.)
Q: Describe the process of transcription, including where it occurs and what enzyme is involved.
A: Transcription occurs in the nucleus. RNA polymerase binds to the promoter region of a gene, unwinds the DNA double helix, and reads the template strand (3' to 5'). It builds a complementary mRNA strand (5' to 3') using free RNA nucleotides. In eukaryotes, the mRNA is then processed (introns removed, cap and tail added) before it leaves the nucleus for translation.
Q: A cell is observed with its chromosomes lined up along the metaphase plate. What phase of mitosis is it in, and what happens next?
A: The cell is in metaphase. Next, it enters anaphase, during which the centromeres split and sister chromatids are pulled to opposite poles of the cell by spindle fibres.
Q: Explain how negative feedback regulates blood glucose after a meal.
A: After eating, blood glucose rises. The pancreas detects this increase and releases insulin. Insulin signals body cells to absorb glucose and signals the liver to convert glucose to glycogen for storage. Blood glucose falls back toward the set point. If it drops too low, the pancreas releases glucagon, which stimulates the liver to break glycogen back into glucose. This opposing response is what makes it negative feedback.
Q: Name the four tissue types and give one location in the body where each is found.
A: Connective tissue (bone, blood, tendons), epithelial tissue (skin surface, lining of the intestine), muscle tissue (skeletal muscles, heart wall, intestinal wall), nervous tissue (brain, spinal cord, peripheral nerves).
Q: What is the difference between apoptosis and necrosis?
A: Apoptosis is programmed, orderly cell death: the cell shrinks, its DNA is fragmented, and it is quietly consumed by neighbouring or immune cells without triggering inflammation. Necrosis is uncontrolled cell death caused by injury (e.g. trauma, toxins, infection), and it does trigger an inflammatory response.
Protein synthesis connects directly to cell structure: the proteins built by ribosomes become the enzymes, receptors, and structural components discussed in the membrane biology notes (Doc 1).
The cell cycle connects to tissue repair and cancer biology. Uncontrolled cell division (failure of cell-cycle checkpoints) is the basis of tumour formation, a topic you will revisit in pathology.
Homeostasis ties together every organ system in the course. The nervous system and endocrine system are the body's two main control systems, and nearly every organ-system chapter will include a homeostatic feedback example.
DNA, RNA, mRNA, tRNA, rRNA, transcription, translation, gene expression, central dogma, nucleotide, nitrogenous bases, adenine, thymine, cytosine, guanine, uracil, base pairing, RNA polymerase, codon, anticodon, ribosome, polypeptide, protein synthesis, connective tissue, epithelial tissue, muscle tissue, nervous tissue, skeletal muscle, cardiac muscle, smooth muscle, neurons, neuroglia, organ, organ system, cell cycle, interphase, G1 phase, S phase, G2 phase, mitosis, prophase, metaphase, anaphase, telophase, cytokinesis, differentiation, stem cells, apoptosis, programmed cell death, necrosis, homeostasis, negative feedback, positive feedback, receptor, control centre, effector, set point, insulin, glucagon, blood glucose regulation, oxytocin, blood clotting, anatomy and physiology, BIO 101