Anatomy Notes Week 2 PDF

The Cell 2. Cytoplasm All cellular material between the cell membrane and the nucleus A) cytosol = gel-like intracellular fluid (ICF); mainly H2O  suspension of carbohydrates, proteins, lipids, and dissolved ions (thus is site of many chemical reactions)  higher [K+] and lower [Na+] than extrace...

The Cell 2. Cytoplasm All cellular material between the cell membrane and the nucleus A) cytosol = gel-like intracellular fluid (ICF); mainly H2O  suspension of carbohydrates, proteins, lipids, and dissolved ions (thus is site of many chemical reactions)  higher [K+] and lower [Na+] than extracellular fluid (ECF) B) organelles – specialized cellular compartments  each performs specific functions essential for cell life i) non-membranous organelles  are in direct contact with the cytosol Organelles a) ribosomes – sites of protein synthesis  contain ribosomal RNA (rRNA) and proteins  either floating free in the cytosol or attached to the endoplasmic reticulum b) centrosomes – dense area of cytoplasm  microtubule organizing center of the cell; organizes the cytoskeleton  forms spindle apparatus for mitosis/meiosis  the centrosome of most cells contains a pair of microtubules (centrioles); function uncertain  thought that centrioles may help direct movement of chromosomes during cell division centrioles Organelles c) cytoskeleton – internal scaffolding of cell  composed of protein filaments  important for cell shape, cell division, structural support, and the anchoring and movement of organelles i) microfilaments – made of actin subunits  help determine cell shape; assist cell motility ii) intermediate filaments – tough protein filaments  secures organelles in place; provides strength and flexibility  anchor cells together; protein composition is tissue specific iii) microtubules – hollow tubes made of tubulin  forms centrioles, spindle, cilia, and flagella  movement of organelles within the cytosol Organelles ii) membranous organelles – all have bilayer membranes  separates these organelles from the cytosol, allowing them to regulate their internal environment a) mitochondria – ‘power plants’ of cells; major site of ATP synthesis  enclosed by two separate bilayer membranes; a smooth outer membrane and a highly folded inner membrane  contain their own DNA (mtDNA), RNA, and proteins enzymes ribosome matrix inner membrane mitochondrial DNA outer membrane Organelles b) endoplasmic reticulum (ER)  network of interconnected membrane channels Rough ER – ribosomes attached  site of secretory, lysosomal, and membrane protein synthesis Smooth ER – no ribosomes  continuous with the RER  functions vary with organ but include: i) lipid and steroid hormone synthesis ii) drug and toxin detoxification Organelles c) Golgi apparatus (Golgi complex)  stacks of membrane disks  sorts, modifies, packages, and delivers proteins and lipids to the plasma membrane, to lysosomes, or for secretion wastes d) lysosomes  filled with digestive enzymes down bacteria, and old/damaged organelles and cells Golgi apparatus  breaks food particle lysosome The Cell 3. Nucleus – DNA containing control center of the cell  the largest membranous organelle Note: some cells have more than 1 nuclei A) nuclear envelope – has two (inner and outer) bilayer membranes  outer nuclear envelope chromatin nucleolus ER membrane contains many pores, and is continuous with the ER B) nucleolus (nucleoli) – non-membranous  dense, dark staining bodies of DNA, RNA, and proteins within the nucleus (generally 1 or 2 per cell)  sites of ribosome production pores The Cell: Nucleus C) chromosomes/chromatids  composed of DNA coiled around histone proteins  found in two states i) DNA strands not individually visible – chromatin  most common state; present when cells are not dividing chromatin chromosome DNA histones 100,000 bp loop sister chromatids ii) chromosomes – condensed, individually visible bar-like bodies found only during the process of cell division  either as single ‘bars’, or as a pair of sister chromatids Somatic cells All cells of the body except those undergoing or resulting from meiosis XY The nuclei of each somatic cell contains 46 chromosomes (23 from mother [ovum] and 23 from father [sperm]): 23 chromosome pairs → 22 autosomal pairs → (encode somatic characteristics) 1 sex pair (♂/♀) from mother ♀ = 22 pairs + XX ♂ = 22 pairs + XY from father Genes – ‘functional’ segments of DNA found within each chromosome; the unit of heredity  each contains ‘instructions’ for the synthesis of a protein(s) Somatic cells Each autosomal chromosome pair is not identical, but equivalent = homologous chromosomes (1 from each parent) i.e. are highly similar in length and centromere position, and (generally) have genes for the same traits (e.g. eye colour) at the same position (locus) on both chromosomes, but... ...they may have different versions (alleles) of certain genes allele for blue eyes ♂ locus for eye colour gene homologous pair of chromosomes ♀ allele for brown eyes e.g. a gene may encode for blue eyes (from Dad), but that same gene on the other chromosome may encode for brown eyes (from Mom) The Cell Life Cycle Series of changes that a cell goes through from the time it is formed until it replicates; essential for growth and repair Interphase S G1 G2 M 1. Interphase – period of normal cell activities and growth  DNA and histone proteins present as chromatin a) G1 phase – rapid cell growth, increased protein synthesis  cells that no longer divide said to be in the G0 phase The Cell Life Cycle b) S (synthetic) phase  DNA replicates, new histone proteins are made  resulting chromatin pairs (each strand termed a chromatid) held together by centromeres  kinetochores (protein) sister chromatids form on each centromere  site of attachment of spindle microtubules c) G2 phase – additional growth and protein synthesis  production of enzymes and proteins needed for cell division  centrosome replication (initiated in G1) is completed The Cell Life Cycle Summary G1 chromatid (23 pairs) ~8–10 hrs S centromere sister chromatids G2 kinetochore DNA replication prepare for cell division ~6–8 hrs ~4–6 hrs Note: chromosomes are not visible during any of these stages The Cell Life Cycle 2. Cell division – ‘M phase’  essential for growth, tissue repair, and reproduction Involves: i) mitosis – division of the nuclear material ii) cytokinesis – division of the cytoplasm A. Mitosis – production of two identical daughter cells (~1 hr)  occurs only in somatic cells prophase (late) prophase (early) metaphase anaphase interphase telophase A. Mitosis i) prophase  chromatin condenses  the and coils, becoming visible nuclear envelope disintegrates, nucleolus disappears  the centrosomes move to opposite sides (poles) of the cell  the spindle apparatus grows out of the centrosomes and attaches to kinetochore proteins on each chromosome  the spindles begin pulling chromosomes towards cell equator ii) metaphase  all 46 double-stranded chromosomes line up along the cell equator A. Mitosis iii) anaphase  centromeres  the split, creating 92 single-stranded chromatids spindle pulls 46 chromatids towards each pole  cytokinesis (division of cytoplasm) begins iv) telophase  the spindle apparatus disassembles  the chromatids uncoil and the nucleolus reappears a nuclear envelope forms around each chromatid mass  cytokinesis ends – the two cells split B. Mitosis: summary 2n 23 pairs of chromatids (46 chromatin strands) 1 2 … 23 ♀♂ ♀♂ XY DNA replication (S phase) Interphase … 2n 46 double stranded chromosomes (each has sister chromatids) … Mitosis 2n … ♀♂ ♀♂ X Y 2n 23 chromatid pairs (46 chromatin strands) … ♀♂ ♀♂ XY The Cell Life Cycle B. Meiosis – production of gametes One diploid (2n) cell creates four genetically distinct haploid (1n) cells interphase meiosis I meiosis II Prior to meiosis, the events of interphase are unchanged  i.e. DNA replicates, centromeres develop, etc. B. Meiosis: similarities to mitosis i) prophase I & II  chromatin condenses into chromosomes  the nuclear envelope and nucleoli disappear  spindle apparatus forms and joins to the kinetochores ii) anaphase I & II  cytokinesis begins iii) telophase I & II  spindle apparatus disassembles  chromosomes  the → chromatin nucleoli and nuclear envelope reappear  cytokinesis completion signals the end of these stages B. Meiosis: processes unique to meiosis Reduction in chromosome number from 2n to 1n Meisois I – ‘reduction division’ (i.e. 1 diploid into 2 haploid cells) i) prophase I  each homologous pair of chromosomes attaches together, forming a tetrad (i.e. 23 separate tetrads are formed) homologous chromosomes (each with sister chromatids) a tetrad over can occur between chromatid strands within each homologous pair (increases diversity of offspring)  crossing B. Meiosis: unique to meiosis ii) metaphase I  the 23 tetrads line up at the cell equator iii) anaphase I  the tetrads split – sister chromatids of each chromosome still connected by centromeres  random segregation of the 23 maternal and paternal chromosomes; one from each pair is moved towards the opposite poles of the cell iv) telophase I Result: each 1n daughter cell lacks homologous chromosomes B. Meiosis Interkinesis – an ‘interphase-like’ period  however, no DNA replication occurs during this phase Meiosis II – separation of sister chromatids  phases equivalent to the events of mitosis i) prophase II  chromatin condenses; nuclear envelope/nucleoli disappear; spindle apparatus forms ii) metaphase II  the 23 double-stranded chromosomes of each daughter cell line up at the cell equator B. Meiosis: meiosis II iii) anaphase II  centromeres  spindle split, creating 46 single-stranded chromosomes pulls 23 chromosomes towards each pole iv) telophase II  spindle apparatus disassembles, chromosomes uncoil, nuclear envelope and nucleolus reappear, cytokinesis Result: four (1n) gametes, each with 23 chromatin strands B. Meiosis: summary 2n = cell with two complete sets of chromosomes 46 chromatin strands (23 chromatid pairs) 1 2 … 23 2n ♀♂ ♀♂ XY DNA replication (S phase) 46 double-stranded … chromosomes (each has ♀♂ ♀♂ XY Interphase sister chromatids) 2n … Meiosis I n … ♂♀ X n Interkinesis Meiosis II n … ♂♀ X n … ♂♀ X n = cell with one complete set of chromosomes tetrads form; crossing over occurs* independent … ♀♂ Y assortment 23 chromosomes (each has sister chromatids) n … ♀♂ Y n … ♀♂ Y 23 chromatin strands Gamete production ♂ meiosis I 1º spermatocyte ♀ 1º oocyte meiosis II two 2º spermatocytes four sperm one ovum* polar body one 2º oocyte (ovulated) * only if fertilized one polar body two polar bodies Fertilization – begins when haploid sperm penetrates a 2º oocyte  triggers completion of meiosis II  fusion in oocyte (becomes ovum) of ♂ and ♀ pronuclei (1n) → zygote (2n)