Cells and homeostasis Flashcards
What are the 3 basic principles of cell theory?
-All living organisms are composed of one or more cells.
-A cell is the basic structural and functional unit of living organisms.
-All cells arise from pre-existing cells.
Cell structure
cytoplasm
cytosol
organelles (mitochondria, smooth endoplasmic reticulum (SER), rough endoplasmic reticulum (RER), Golgi apparatus, lysosomes, cytoskeleton, centrioles, ribosomes)
Nucleus
All body cells have at least 1 nucleus.
Largest organelle and contained within nuclear envelope.
Contains body’s genetic material
Also contains the nucleolus, involved in synthesis of some ribosomes
Endoplasmic reticulum
Extensive series of interconnecting membranous canals. Two types, smooth and rough
Smooth - synthesises lipids, steroid hormones and vesicles to transport them to other parts of the cell
Rough - studded with ribosomes, site of protein synthesis. Enzymes and hormones are exported out the cell by exocytosis for use elsewhere
Vesicle
A structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer’ used for transportation
Ribosomes
Granules of RNA and protein.
Uses the RNA to synthesise proteins from amino acids for use in the cell.
Found on outer surface of nuclear envelope and RER.
Mitochondria
Powerhouse of the cell.
Central to aerobic respiration, making chemical energy in the form of ATP.
Released energy when cell breaks down ATP.
This process requires oxygen.
Most active cell types have greatest number of mitochondria.
Golgi apparatus
Stacks of folded flattened membranous sacs with vesicles budding from it.
Proteins move from RER to golgi where packaged into membrane bound vesicles. These are stored for when needed.
lysosomes
Small vesicles pinched off from the golgi.
Membrane bound.
Contain enzymes and large molecules like DNA, carbohydrates, proteins.
Cytoskeleton
Extensive network of tiny protein fibres.
Provides internal support for the cell, Anchors organelles as well as guiding movement around cell interior.
Microfilaments
protein fibres anchored to inside of cell membrane, giving support and shape
Microtubules
large rigid proteins giving mechanical support, providing guidance tracking for internal movement.
Centrosome
directs organisation of microtubules within the cell. Consists of pair of centrioles.
Plasma membrane
Selective barrier, controls passage of substances in and out of the cell, regulating intracellular environment.
How many layers of phospholipids are there?
Two layers of phospholipids with proteins, cholesterol and glucolipids imbedded.
What are phospholipids?
Phospholipids have a hydrophilic head and hydrophobic tail. Heads on outer surfaces, tails sandwiched in between. Affects how substances are transported across the membrane.
Particle size affects how transported across membrane, if at all.
What are the 2 kinds of transport?
passive and active.
Diffusion + facilitated diffusion
The movement of molecules from an area of high concentration to an area of low concentration.
Factors can affect the rate, including temperature or concentration.
Molecules need to be small or soluble enough to cross membrane with diffusion alone.
Lipid soluble materials cross the lipid part of the membrane. Water soluble cross through water-filled channels.
Facilitated diffusion- some substances unable to diffuse across membrane, e.g. glucose, amino acids. need protein carrier molecules to aid diffusion.
Osmosis
osmosis refers specifically to diffusion down a concentration gradient.
Usually because other molecules are too large to pass through membrane
Force at which this occurs is called osmotic pressure.
Movement is to achieve equilibrium in concentration not necessarily volume, this is called isotonic
Active transport
Transporting substances up the concentration gradient from lower concentration gradient to higher concentration gradient.
To do this requires energy in the form of ATP
Sodium potassium pump - supports transport mechanisms such as glucose uptake.
Also is essential in maintaining the electrical gradient needed to generate action potentials in nerve and muscle cells.
Active transport maintains the unequal concentrations of sodium and potassium ions either side of plasma membrane.
Cell cycle
An ordered sequence of events including duplication of cellular contents and division that all cells follow.
For growth and repair.
The rate of replication varies with different types of tissues.
Aged cells ‘self destruct’ known as apoptosis.
Cell cycle: What are the 4 discrete phases?
G1 - gap phase - cells grow in size, some do not prepare for division but instead, ‘rest’ (G0)- specific cellular functions. Cells may stay in G0 for whole life span.
S - synthesis phase, DNA replication, 2 identical copies. Cell now has 92 chromosomes
G2 – gap phase, further growth and preparation for division
M – mitosis phase, cell divides
What are the 2 types of cell division?
Mitosis and meiosis
Explain mitosis
-Occurs in somatic (non-reproductive) cells for growth and repair
-One round of replication
-One division
-1 parent cell produces two identical daughter cells (2n)
-No genetic diversity
-cell contains 46 chromosomes
Explain meiosis
-Occurs in reproductive cells- formation of gametes (egg and sperm)
-Not a ‘cell cycle’, linear because of its products
-One round of DNA replication
-Two successive divisions
-Results in four different daughter
cells that contain half the number of chromosomes of the parent cell (1n)
- Each daughter cell contains 23 chromosomes, haploid cells
5 stages of mitosis
Prophase - Chromosomes appear condensed, nuclear envelope no longer apparent. Centrioles begin moving to opposite ends of the cell and fibres extend from the centromeres.
Metaphase - Spindle fibres align the thick, coiled chromosomes, each made of 2 chromatids, along the middle of the cell nucleus; referred to as the metaphase plate.
Anaphase - The paired sister chromatids separate and move to opposite sides of the poles of the cell as the spindles shorten.
Telophase - Chromatids arrive at opposite poles of cell, and new nuclear membranes form around the daughter nuclei. Chromosomes become more diffuse. Spindle fibres disperse, cytoplasm may begin dividing.
Cytokinesis - Cell division is complete and two identical daughter cells are produced. Chromosomes start to decondense, and the cells return to interphase.
Meiosis- Genetic recombination
Genetic recombination happens in meiosis. Where two molecules of DNA exchange parts of genetic material when homologous chromosomes are lined up in pairs.
This is known as chromosomal crossover or “crossing over”
Results in new genetic combinations – creates genetic variation/diversity
Due to genetic recombination, any offspring will have a different combination of alleles and genes than their parents do
Homeostasis
Keeping a stable constant internal environment via use of negative feedback e.g. regulating temperature and chemical levels.
The homeostatic process ensures that variables never deviate outside of the normal perimeter
Afferent pathway- to the control center
Efferent pathway- to the effectors
Stimulus detected- deviation from set point
Receptors detect these changes
Control centre generates a response to make changes
Effectors carry out that response
Homeostasis: What are the 2 types of bodily fluid
Intracellular fluid- within cells
Extracellular fluid- outside cells
Content of both fluids is: water, oxygen, nutrients, proteins and various ions
Homeostasis: Types of extracellular fluid
Interstitial fluid- around cells and tissues
Plasma- within the blood
Lymph- within lymphatic vessels
Cerebrospinal fluid- around and in the brain and spinal cord
Synovial fluid- within joints
What happens to the composition of fluid during homeostasis?
Composition of fluid changes as it moves between it and blood plasma due to various forces; hydrostatic pressure (force pushing fluid out of vessels occurs in arteries due to heart pumping) and osmatic pressure (due to concentration differences, passing from high concentration to low concentration tends to occur at venous ends).
This process allows the movement of materials into the interstitial required by cells and the removal of waste products e.g. carbon dioxide.
Homeostatic imbalances can result in disorder and disease.
What are feedback systems and what are the 2 types?
Generally the nervous and endocrine system tend to be responsible for maintaining homeostasis. These systems can work independently or together.
The nervous system sends nervous impulses.
The endocrine results in the release of hormones into the blood.
Two types of feedback system:
-Negative feedback
-Positive feedback - amplification of symptoms.
Examples of positive feedback include contractions/labour and breastfeeding
Feedback systems: What affects the body’s control system?
Age affects the body’s control system becoming less efficient resulting in a less stable internal environment.
Occasionally the negative feedback system can become overwhelming and the positive feedback system results leading to potentially life-threatening situation (heart failure).
