Cell Physiology Flashcards
What percentage of body weight is total body water in a dog, and how is it distributed?
Total body water in a dog is approximately 60% of body weight.
It is distributed as 1/3 extracellular fluid (ECF) and 2/3 intracellular fluid (ICF).
Define homeostasis
Homeostasis is the maintenance of a nearly constant internal environment.
What are the key differences in ion composition between extracellular fluid and intracellular fluid?
Extracellular fluid contains mainly Na, Cl, and HCO₃, Intracellular fluid contains primarily K, Mg, and PO₄.
Describe negative feedback in body control systems with an example.
Negative feedback occurs when an increased value triggers a compensatory mechanism that decreases the value (negative to the initiating stimulus).
Example: When arterial blood pressure rises, baroreceptors signal to lower it back to normal range.
What is the formula for calculating the gain of a control system?
Gain = Correction/Error
The gain determines the effectiveness with which a control system maintains constant conditions.
When can positive feedback be useful in physiological systems?
Positive feedback, though potentially dangerous (creating “vicious cycles”), can be useful in processes such as blood clotting, uterine contractions during childbirth, and nerve signal generation.
What are the two main systems for protection of the body
Immune system and integument
What are the two main mechanisms for regulation of body functions
nervous system and hormones
What are structural proteins
Long filaments often forming microtubules to provide cytoskeleton of cellular organelles
What are functional proteins
Tubular globular forms that act as enzymes, often mobile; can adhere to cell membrane to catalyse reactions
What is the composition of the cell membrane
55% protein, 25% phospholipid, 13% cholesterol, 4% other lipid, 3% carbohydrates
What substances can easily penetrate the lipid bilayer
Fat-soluble substances (O₂, CO₂, alcohol)
What is glycocalyx and what are its functions
A loose coat of proteoglycans around the cell, formed by glycoproteins or glycolipids that protrude from the cell surface
Repels negatively charged objects, attaches cells together, serves as receptors for hormone binding, activates intracellular enzymatic reactions, and participates in immune reactions
What is the difference between rough ER and smooth ER
Rough ER has ribosomes attached to its outer surface and is involved in protein synthesis;
Smooth ER lacks ribosomes and is involved in lipid synthesis (mainly cholesterol and phospholipids)
What is the function of the Golgi apparatus
It processes vesicles from the ER to form lysosomes, secretory vesicles, and other cytoplasmic components
What are lysosomes
Vesicles that break off from the Golgi apparatus, containing hydrolase enzymes that function as the cell’s digestive system
What do peroxisomes contain
Oxidases, hydrogen peroxide, and catalase
What is the main function of mitochondria
Oxidation of nutrients to form CO₂, H₂O, and energy, which is used to form ATP
What is the function of microfilaments
They provide elastic support and enable muscle contraction (actin/myosin)
What is the function of intermediate filaments
They provide strength and support to the cell
What is the function of microtubules
They provide strength and structure to the cytoskeleton, and form centrioles and mitotic spindles
What is the function of the nucleus
It serves as the control centre for cell growth, maturation, replication, and death
What are nucleoli
Structures within the nucleus (without a membrane) that contain large amounts of RNA and proteins, involved in ribosome formation
What is pinocytosis
Ingestion of minute particles that occurs continuously in the cell membrane
What is phagocytosis
Ingestion of large particles, bacteria, or whole cells by specialized cells like macrophages and some leukocytes
What happens in a digestive vesicle
Lysosomes empty hydrolases into pinocytic vesicles, forming digestive vesicles where hydrolysis products can diffuse through the membrane
What is autophagy
The process where organelles are transferred to lysosomes by autosomes, which fuse with lysosomes to form autophagosomes, allowing nutrients to be reused by the cell
What antibacterial agents do lysosomes contain
Lysozyme (dissolves bacterial cell walls),
Lysoferrin (binds iron to prevent bacterial growth),
and an acidic pH that activates hydrolases and inactivates bacterial metabolism
What is ATP composed of
A nitrogenous base (adenine), a pentose sugar (ribose), and three phosphate radicals
What percentage of cellular ATP is formed in mitochondria
95%
What are three major uses of ATP in cellular function
Transport of substances through cell membranes,
Synthesis of chemical compounds,
Mechanical work
What is ameboid movement and what cells use it
A form of cell movement where new membrane formation causes pseudopodia to project forward, followed by receptor binding and actin filament contraction to pull the cell forward
White blood cells, tissue macrophages, fibroblasts, embryonic cells, and neoplastic cells
What is chemotaxis
The process that initiates cell movement toward (positive) or away from (negative) a chemical substance
What is the structure of cilia
11 microtubules - 9 doubles and 2 single in the centre, which are outgrowths of the basal body
What are the two types of cilia
Motile cilia (with whip-like motion) and non-motile cilia (serving as sensory antennae)
Motile cilia - Respiratory airways and fallopian tubes
What is required for ciliary movement
ATP (causes dynein protein to project), calcium, and magnesium
What are the basic chemical components of an acidic nucleotide in DNA?
Phosphoric acid, deoxyribose sugar, and a nitrogenous base (either purine or pyrimidine)
What are the two types of nitrogenous bases in DNA, and which bases belong to each type?
Purines (adenine, guanine) and pyrimidines (thymine, cytosine)
What is the base pairing rule in DNA?
Adenine always pairs with thymine, and guanine always pairs with cytosine
What is a triplet in genetic code?
A triplet is a sequence of three bases that forms a code word, with each triplet responsible for coding a specific amino acid
How does RNA differ from DNA?
RNA uses ribose (contains extra hydroxyl ion) instead of deoxyribose,
RNA uses uracil instead of thymine as a pyrimidine base
What are the four nucleotides in RNA?
Adenine (A), uracil (U), cytosine (C), and guanine (G)
How are RNA nucleotides activated?
By RNA polymerase adding two extra phosphate radicals to form triphosphates, using ATP to add new nucleotides to the end of the developing chain
What is Pre-mRNA and what are its components?
Precursor messenger RNA is a large single strand of RNA processed in the nucleus to form mRNA
it includes introns (removed by splicing) and exons (retained in mRNA)
What is the function of small nuclear RNA (snRNA)?
It directs the splicing of pre-mRNA to form mRNA
What is the function of messenger RNA (mRNA)?
It carries genetic code from the nucleus to the cytoplasm to control protein formation
How does transfer RNA (tRNA) function in protein synthesis?
tRNA transports activated amino acids to ribosomes
it recognizes specific codons on mRNA through its anticodon, delivering the appropriate amino acid to the right place in the protein chain
What is the structure and function of ribosomal RNA?
Ribosomal RNA, along with 75 different proteins, forms ribosomes where proteins are assembled; it works in association with mRNA and tRNA
What is microRNA (miRNA) and its function?
miRNA consists of single-strand RNA molecules that regulate gene transcription and translation
It binds to mRNA, causing repression of translation or degradation of the mRNA
What is transcription?
The process where DNA code is transferred to RNA
What are the main steps in RNA chain assembly during transcription?
1) RNA polymerase attaches to the promoter on DNA
2) DNA unwinds and separates
3) Polymerase moves along and adds RNA nucleotides to the chain
4) Chain terminating sequence causes polymerase to break away, and the new RNA chain separates from DNA
What are polyribosomes?
Clusters of ribosomes (3-10) attached to the same mRNA
What is the TATA box and its function?
The TATA box is a sequence of bases (TATAAA) in the basal promoter that serves as the binding site for TATA-binding protein and transcription factor IID complex
RNA polymerase must bind to the basal promoter before it can synthesize RNA.
What are enhancers in gene regulation?
Enhancers are regions of DNA that can bind to transcription factors and can be located far from the gene they regulate
What are insulators in genetic regulation?
Insulators are gene sequences that provide a barrier between active and suppressed genes; they can be modulated by DNA methylation
What are histones
DNA is wound around histone proteins in chromosomes.
When wound tightly, DNA cannot form RNA; specific mechanisms can unwind selected areas to allow gene expression
How does DNA replication differ from RNA transcription?
In DNA replication: both DNA strands are replicated, replication occurs from end to end, DNA polymerase (not RNA polymerase) is used, and DNA ligase bonds nucleotides together
What is the role of DNA helicase in replication?
DNA helicase enzymes break down hydrogen bonds between base pairs to allow ‘unzipping’ and replication fork formation
Why is DNA replication only in the 5’ to 3’ direction?
DNA polymerase can only add nucleotides to the 3’ end of a growing DNA strand
What are Okazaki fragments?
Short, newly synthesized DNA fragments that are formed on the lagging strand during DNA replication and later joined by DNA ligase
What is the role of topoisomerase in DNA replication?
Topoisomerase breaks phosphodiester bonds in the DNA backbone to prevent overwinding in the helix in front of the replication fork
What are the main phases of mitosis?
Prophase, prometaphase, metaphase, anaphase, and telophase
What happens during prophase?
The spindle forms and chromosomes condense
What occurs during metaphase?
Chromatids are pulled tightly by attached microtubules to the center of the cell, forming the equatorial plate of the mitotic spindle
What happens during anaphase?
Chromatids are pulled apart at the centromere, separating 46 chromatids into 46 daughter chromosomes, with one set pulled toward each aster
What occurs during telophase?
The two sets of daughter chromosomes are pushed completely apart, the mitotic apparatus dissipates, new nuclear membranes form, and the cell pinches in two due to a contractile ring of microfilaments
What are telomeres and their function?
Telomeres are regions of repetitive nucleotide sequences at the end of chromosomes that prevent degradation of chromosomes and act as a protective cap to prevent loss of genome
How do telomeres relate to cell aging?
When telomeres shorten to a critical length, chromosomes become unstable and cells die; telomere erosion is caused by cell division, oxidative stress, and inflammation
What is the role of telomerase?
Telomerase is an enzyme that adds bases to the ends of telomeres in certain cells like stem cells
In cancer cells, telomerase activity is activated and allows uncontrolled replication
What is apoptosis?
Programmed cell death involving a proteolytic cascade that causes cell shrinkage, condensation, cytoskeleton disassembly, and membrane changes to allow phagocytosis by macrophages
How is apoptosis initiated?
By activation of caspases, which are protease enzymes stored in cells as inactive procaspases
How does apoptosis differ from necrosis?
In apoptosis, cells undergo programmed death
In necrosis (due to injury), cells swell and burst, causing inflammation and injury to nearby cells
What are proto-oncogenes? What are oncogenes?
Genes that code for proteins controlling cell adhesion, growth, and division
when mutated, they become oncogenes responsible for cancers
What are tumor suppressor genes?
Anti-oncogenes that suppress the activation of specific oncogenes
Why do only a small proportion of mutated cells cause cancer?
Mutated cells often have less survival capacity,
Most still have normal feedback control to prevent excessive growth,
Many are destroyed by the body’s immune system
What gives cancer cells their invasive characteristics?
Cancer cells don’t respect usual cellular growth limits,
Less adhesive than normal cells,
Produce angiogenic factors that promote blood vessel growth and nutrient supply
How do cancer cells kill?
By competing for nutrients and disrupting vital organ function
