week 2: the cell

cell/plasma membrane

outer boundary of the cell

• selectively permeable

  • divides intracellular fluid from extracellular

cell membrane: phospholipid bilayer

cell membrane: membrane proteins

• function:

  • enzymes

  • form ion channels

  • transporters

  • hormone receptors

  • cell anchors

  • identity markers → for immune system

membrane proteins: integral vs peripheral proteins

• integral: have hydrophobic and hydrophilic regions

  • transmembrane proteins: the ones that span the membrane completely

• peripheral: attached to integral proteins on inner/outer surface of bilayer

cell membrane: membrane carbs

only on outer surface of cell

• bound to proteins/glycoproteins or lipids/glycolipids

• used to anchor cells together and for cell-to-cell recognition

  • ie: eggs, sperm

fluid-mosaic model of the cell membrane

cell surface is constantly changing as phospholipids and proteins are free to float around

cytoplasm

all cellular material between the cell membrane and nucleus

cytosol

gel-like ICF → mainly H2O

• suspension of carbs, proteins, lipids, dissolved iron

  • site of many chemical reactions

• higher K+ and lower Na- than ECF

• may include inclusions → ie: melanin, glycogen

nuclear envelope

has 2 bilayer membranes → inner and outer

• membrane is continuous with the ER

  • contains many pores

nucleolus (nucleoli)

• non-membranous

• dense, dark staining region of DNA, RNA, proteins within the nucleus

  • generally 1 or 2 per cell

• site of ribosome production and assembly

chromosomes/chromatid

• composed of DNA coiled around histone proteins

• found in 2 states

chromatin

DNA strands not individually visible

• most common state

• present when cells aren’t dividing

chromosomes

condensed, individually visible bar-like bodies found only during the process of cell division

• either:

  • single bars

  • pair of sister chromatids

somatic cells

all cells of the body except those undergoing/resulting from meiosis → gametes

• nuclei is diploid → 2n = 46 chromosomes

autosomal chromosome pair

not identical but equivalent → 1 homologous chromosome from each parent

• similar in length, centromere position, have genes for same traits at same locus

  • may have different alleles of genes

interphase

period of normal cell metabolism and growth

• DNA and histone proteins present as chromatin

• cells that no loner divide are in G0 phase

interphase: G1 phase

• rapid cell growth

• centrosome replication begins

interphase: S/synthetic phase

• DNA replicates, new histone proteins are made

• resulting chromatin pairs → each strand termed a chromatid

  • held together by centromeres

• kinetochores (protein) form on each centromere

  • site of attachment of spindle microtubules

interphase: G2 phase

additional growth and protein synthesis

• production of enzymes and proteins needed for cell division

• centrosome replication is completed → is initiated in G1

cell division: M-phase

essential for growth, tissue repair, reproduction

• involves:

  • mitosis: division of the nuclear material → chromosomes

  • cytokinesis: division of the cytoplasm

mitosis

production of 2 identical daughter cells → 1hr

• occurs only in somatic cells

mitosis: prophase

• chromatin condenses, coils → becomes individually visible

• nuclear envelope disintegrates, nucleolus disappears

• centrosomes move to opposite poles of the cell

• microtubules grow + attach to kinetochore proteins = spindle apparatus

• spindles begin moving chromosomes towards cell equator

mitosis: metaphase

• all 46 double-stranded chromosomes line up along cell equator

mitosis: anaphase

spindle microtubules shorten causing centromeres to split → 92 single-stranded chromatids

spindle pulls 46 to each pole

cytokinesis beings

mitosis: telophase

• spindle apparatus disassembles

• chromatids uncoil and nucleolus reappears

• a nuclear envelope forms around each chromatin mass

• cytokinesis ends → the two cells split

meiosis

production of gametes

• one diploid (2n) creates 4 genetically distinct haploid (1n) cells

meiosis: similarities to mitosis

• prophase 1 and 2

• anaphase 1 and 2

• telophase 1 and 2

meiosis: unique processes

• P1: homologous chromosomes pair and align gene-to-gene during synapsis = tetrad

  • crossing over between non-sister chromatids occurs here

• M1: tetrad orientation during lining up is independent of others

• A1: separation of homologous chromosomes → sister chromatids remain attached at the centromere

• produces haploid cells

interkinesis

interphase like period

• no DNA replication occurs during this phase

• happens before meiosis 2

cell membrane composition

phospholipid bilayer + cholesterol (stability) + membrane protein (integral + peripheral) + membrane carbs

2 divisions of the cytoplasm

1. cytosol: gel-like fluid = H20 + ions + suspended molecules

2. organelles

3 types of cytoskeletons

1. microfilaments: made of actin

2. intermediate filaments: tissue specific → ie: keratin

3. microtubules: hollow tubes of tubulin