Download ANPS 019 Beneyto-Santonja 09-07

ANPS 019 09/07/12 Beneyto
Summary of Transport Processes
Passive Processes
1. Simple Diffusion
2. Osmosis
3. Facilitated Diffusion  ‘Carrier mediated’
Active Transport
 Energy required: consumed ATP
 Independent of concentration gradients
o Moves substance ‘uphill’ or from area of low concentration to are of high
concentration
 Types of active transport include
o Primary active transport; ex. Ion pumps
o Secondary active transport; ex. Nutrients
Primary Active Transport: The Sodium Potassium Exchange Pump
 Critical to cell function; creates ionic difference across cell membrane
 Membrane Enzyme: sodium-potassium ATPase
 Requires ATP
 Moves 3 sodium ions out, 2 potassium ions in
 Pump, Not channel (antiporter)
Secondary Active Transport
 Transporter does not require energy, but the gradient for solute movement is created by
energy use elsewhere in cell
 As long as the sodium-potassium ATPase is actively pumping sodium OUT, all of the
transporters here will take advantage of sodium pushing back IN to move other
substances through the membrane.
Vesicular Transport: material moves into or out of cells in membrane-bound vesicles
 Exocytosis is ejection of materials from the cell
o Fusion of a cytoplasmic vesicle with the plasma membrane
o “loose” contents of vesicle are released into extracellular fluid
o vesicle membrane now part of plasma membrane
 Endocytosis is movement of material into the cell
o Pinocytosis
o Receptor mediated endocytosis (coated vesicles)
o Phagocytosis
Pinocytosis = ‘cell drinking’
 Cell ‘drinks in’ extracellular fluid
 Not specific as to what comes in: no receptors involved
 Process:
o Formation of vesicle; fluid and dissolved solutes in vesicle; fusion of lysosome
and vesicle; digestion by lysosmal enzymes; digested solutes in cell
Receptor-Mediated Endocytosis
 Allows the cell to select specific large molecules from the extracellular fluid and bring
them into the cell. Specificity comes from special membrane proteins clustered together
that bind particular substance (ie:iron)
 Extracellular substance bind to membrane receptor
 Membrane pinches in forming cytoplasmic vesicle with substance bound on inside
 Vesicle fused with lysosome; enzymes remove ligand from receptor

Vesicle returns to surface and reinserts into plasma membrane, again exposing receptors
to extracellular fluid.
The active and passive transport properties of a cell leave an uneven distribution of solutes across
the membrane.
 Of special importance is the difference in ion concentrations across the cell membrane
o Creates a difference in the electrical potential between the inside and outside of
the cell- the transmembrane potential
o Key to nerve and muscle function
Two different states of DNA for two main nuclear events
 Chromosome appear just prior to mitosis, division of the nuclear material during cell
division.
 The rest of the time, DNA is in the lose, dispersed form called chromatin, where small
areas of the DNA can be exposed for the process of protein synthesis
Review (DNA)
 DNA has a pair of nucleotide chains
 The chains spiral around one another (Double helix)
 Weak hydrogen bonds holding the two chains together can be easily broke to ‘unzip’ the
spiral and expose bases on each strand.
The Cell Cycle
 For most of a cell’s life, when the cell is in G0 and G1 stages, the DNA is in chromatin
form. These are times of protein synthesis, making different proteins that determine the
cell’s activities
 During the S phase of the cell cycle, the DNA is copied in it entirety in preparation for
cell division. Both ‘daughter cells’ will have a complete set of identical DNA.
 G1: Normal cell functions plus cell growth, duplication of organelles, protein synthesis (8
or more hours)
 S: DNA replication, synthesis of histones (6 to 8 hours)
 G2: Protein synthesis (2 to 5 hours)
 Mitosis: Prophase, Metaphase, Anaphase, Telophase, Cytokinesis (1 to 3 hours)
 G0: Specialized cell functions (indefinite period)
DNA Replication during Cell Division
 The nucleus contains the DNA and a chemical soup which includes both DNA and RNA
nucleotides. In DNA replication, DNA nucleotides will be taken from the nuceloplasm
and linked together under the direction of an enzyme called DNA polymerase to create
new DNA strands.
Chromosomes
 A gene is a small segment on a chromosome which codes for a unique protein
 Therefore, a gene codes for a sequence of amino acids
 Exceptions: Ribosomal RNA (rRNA) & transfer RNA (tRNA)
Overview of Protein Synthesis
1. A particular sequence of DNA is unwrapped
2. A copy of one of the strands is made with RNA bases (transcription)
3. The copy leaves the nucleus and finds a ribosome in the cytoplasm
4. The copy is ‘read’ and a string of amino acids is formed using the RNA code (translation)
5. The new protein is sent elsewhere in the cell for immediate use of final adjustments
The process of transcription leads to the creation of a strand of messenger RNA (mRNA)
containing a code of bases complementary to one segment of one DNA strand.
Transcription: making a copy of one strand of the DNA into RNA (think Transcribe)
Translation: converting a nucleotide sequence into an amino acid sequence (think Translate)
There are 3 kinds of RNA involved in the process
1. Ribosomal RNA – combined with proteins to make ribosomes
2. Messenger RNA – the message strand that carries the code for a protein from the DNA
into the cytoplasm
3. Transfer RNA – Cytoplasmic RNA strand folded into cloverleaf; binds an amino acid at
one end.