WEEK THREE - DNA/RNA, HISTOLOGY, ORGANISATION AND HISTOLOGY OF NERVOUS SYSTEM Flashcards
Structure of DNA and organisation in nucleus
polymer of nucleotides with
- phosphate group
- sugar - deoxyribose
- nitrogenous base
non-dividing state - compacted, around histone protein
dividing state = DNA copies into 2 parallel sister chromatids
base pairing = A-T, C-G
compare the structure and function of DNA vs RNA
RNA - polymer of nucleotides
phosphate group
sugar - ribose
nitrogenous base
RNA = smaller than DNA
only one nucleotide chain not double helix
DNA = CTAG
RNA = CUAG [Uracil replaces Thymine as nitrogenous base]
DNA function - codes for protein synthesis
RNA function - interprets DNA code
Define the genetic code and describe how DNA codes for protein structure
system that enables FOUR nucleotides to code for amino acid sequence of proteins
three nucleotides / amino acids
codon = mirror image sequence of nucleotides found in mRNA
64 possible codons [AUG=start = codes for methionine]
[3 stop codons]
Explain the process of transcription
copying instructions from DNA –> RNA
- RNA polymerase binds to DNA
- opens DNA helix and transcribes bases from 1 strand of DNA into pre mRNA
[DNA ‘C’ = mRNA ‘G’]
[DNA ‘A’ = mRNA ‘U’ - rewinds DNA helix
Explain the process of translation
- RNA reads amino acids assembled into protein molecules in mRNA
- tRNA takes amino acids to ribosomes
- converts nucleotides into sequence of amino acids = proteins
ribosome in cytosol or RER
- small subunit attaches to mRNA leader sequence
- larger subunit joins and pulls mRNA along whilst reading it [from AUG start codon]
- small subunit binds activated tRNA with corresponding anticodon
- large subunit enzyme forms peptide bonds = growth of polypeptide chains
- process repeats until stop codon reached
- polypeptide chain released and ribosome subunits separate
Describe how DNA is replicated
DNA helicase open short segment of helix [creates replication fork]
Primase enzyme binds to spot -annealing RNA primer
DNA polymerase III binds to RNA primer and begins generating complementary strand of DNA
List and describe the 4 main phases of the cell cycle
G1 Phase [first gap phase]
Accumulates materials needed to replicate DNA
S phase [synthesis phase]
DNA replication
G2 [second gap phase]
Replicates centrioles
Synthesises enzymes for division
Growth for preparation for mitosis
M phase [Mitotic]
Nuclear and cytoplasmic division
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
G0 phase [cells that have left the cycle]
List the phases of mitosis and summarise the events that occur in each phase [IPMATC]
One cell divides into TWO DAUGHTER CELLS with identical copies of DNA
Function - growth and replacement of worn out cells
Phases
Interphase
Chromosomes duplicate = two duplicate chromatins joined at centromere
Prophase
Chromosomes condense + nuclear envelope breaks down
Spindle fibres grow from centrioles
Centrioles migrate to opposite poles of cell
Metaphase
Membrane breaks apart
Spindle fibres attaches to chromosome and line up equator of cell
Anaphase
Spindle fiber shortens and centromere divides = becomes two separate chromatins
Two chromatids are pulled to polar ends of cell by spindle fibers and centromeres
Telophase
Chromosomes arrive at cell poles
Nuclear membrane forms around each set of chromosomes
Spindle fibers break down
Cytokinesis
Cell membrane breaks into two separate sets of chromatins
= TWO DAUGHTER CELLS
List and define the 4 primary tissue classes [ECNM] - e-cinema
Epithelial
Layers of closely spaced cells that cover organ surfaces, form glands
Function = protection, secretion, absorption
Connective
Usually moe matrix than volume
Function = often specilised to support, bind and protect organs
Nervous
Tissue contains excitable cells
Functions = rapid transport of coded info to other cells
Muscular
Elongated, excitable muscle cells
Function = contraction
Describe the structural properties that define epithelial tissue
Layers of loosely adhering cells with little extracellular matrix
One or more cells thick
Upper surface usually exposed to environment or internal space in body
Avascular [no room between cells for blood cells]
Relies on the diffusion of nutrients and gases from vessel-rich underlying CT layer
High rate of mitosis with cells closest to the CT layer [allows rapid repair]
List and exemplify 5 functions of epithelial tissue [PSAFS]
Protecting underlying structures
Eg outer layer of skin and epithelium of oral cavity protect underlying structures from abrasion
Secretion of substances
Eg mucous glands, sweat glands, enzyme-secreting portions of pancreas all composed of epithelial cells
Absorption
Absorption of nutrients across epithelium of small intestine
Filtration
Eg kidney epithelia is glomeruli filter out wastes from blood capillaries
Sensation
Epithelial structures with sensory nerve endings are found in the skin, nose, ears and eyes
List & define how epithelia are classified by layers & shape
LAYERS
Simple
Single layer of cells attached to basement membrane
Stratified
More than one layer
Only basal layer attached to basement membrane
Pseudostratified
Type of simple epithelium where epithelium appears to be stratified but is not
Some cells do not extend to free surface
SHAPE
Squamous
Cells are flat and scale-like
Cuboidal
Cube-shaped, as wide as tall
Columnar
Cells taller than they are wide
List the 8 types of epithelia, describe their structure and give examples where they can be found
Simple Squamous Epithelium
Single row of flat cells
Permits diffusion of substances//Secretes serous fluid
Alveoli, glomeruli, endothelium and serosa
Simple Cuboidal Epithelium
Single row cube shaped cells with microvilli
Absorption and secretion, mucus production
Liver, thyroid, mammary and salivary glands, bronchioles and kidney tubules
Simple Columnar Epithelium
Single row, tall narrow cells
Oval nuclei in basal half of cell
Absorption and secretion; mucus secretion
Lining and GI tract, uterus, kidney and uterine tubes
Pseudostratified Epithelium
Single row of cells some not reaching free surface
Nuclei give layer stratified look
Often with goblet cells and ciliated
Secretes and propels respiratory mucus
Typically found in trachea
Keratinised Stratified Squamous
Surface layer of dead cells
Multilayered epithelium covered with dead squamous cells packed with tough protein [keratin]
Retards water loss and barrier to organisms
Found in epidermal layer of skin where abrasion is high
Non-Keratinised Stratified Squamous
Multilayered surface epithelium forming moist, slippery layer
Without surface layer of dead cells
Resists abrasion
Tongue, oral mucosa, oesophagus, anal canal and vagina
Stratified Cuboidal Epithelium
Two or more cell layers; surface cells = square
Secretes sweat; produces sperm and hormones
Sweat gland ducts; ovarian follicles and seminiferous tubules
Transitional Epithelium
Multilayered epithelium surface cells that change from round to flat when stretched
Allows for filling of urinary tract
Lining Of urinary bladder and ureter
Exemplify how the structural differences between epithelia relate to their functional differences
Different tissue types are more suited to particular types of body - some need protection eg keratinized + non-keratinised stratified squamous, whilst others need diffusion of materials across membranes eg simple squamous.
eg Stratified epithelia are found where a barrier is needed and where there is abrasion present
Eg oral cavity and epidermis
Simple epithelium in these areas would just wear way
Describe the structural properties that define connective tissue
Most abundant and variable tissue type
Widely spaced cells - produces intracellular matrix
Multitude of different cell types
