Review
A TOUR OF THE CELL
Cytosol: the fluid portion of the cell
• 55 % of the total cell volume
• 75-90% water
• includes dissolved and suspended components -ions
-ATP
-glucose, amino acids, lipids, proteins -enzymes
-wastes
-fat droplets and glycogen granules
• it is not uniform throughout the cell
• it is the site for many essential chemical reactions of cell metabolism, including glycolysis.
Organelles -"little organs"
• specialized structures with specific shapes and' functions.
• Each has their own set of enzymes appropriate to their functional chemical
reactions.
• Two basic categories:
Non-membranous
-are in direct contact with the cytosol -cytoskeleton, cilia, ribosomes, flagella,
centrosomes
Membranous
-surrounded by membranes similar to the plasma membrane.
-separate interior from the cytosol -mitochondria, golgi apparatus, ER,
lysosomes.
CYTOSKELETON:
1. Functions:
• Framework
• Shape
• Movement
-internal movement -vesicles, spindle fibers
-external movement phagocytosis
• Organizes contents
2. Component Parts -protein filaments
• Microfilaments
-function in movement and mechanical support *cell locomotion
*cell division
*muscle contraction
*anchors for microvilli
*anchors for key cell proteins
*extra-cellular extensions for adhesion to other cells.
-most contain actin
-concentrated at the edges of the cell
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Intermediate filament
-anchor organelles like the nucleus
-very strong, support areas under stress -mid-range in thickness
Microtubules
-largest
-long, unbranched, and hollow -made of "tubulin"
-grow out from the centrosome toward the cell edges.
-microtubules are assembled and disassembled to move vesicles and other cell
components. -push organelles and substances along micr otubules
CENTROSOME
• Made of 2 components:
pericentriolar area
*dense network of small protein fibers
*organizing center for the mitotic spindle
*microtubule formation in non-dividing cells.
centrioles
*formation and regeneration of cilia and flagella.
CILIA and FLAGELLA
1. made of
2. anchored to a basal body just below PM
3. basal body is similar to a centriole -initiates the assembly of cilia and flagella
4. cilia (small and hair-like) exhibit coordinated movement -beating
*line respiratory tract -sweep out foreign particles
5. flagella (longer)
-wavelike wiggle pattern -sperm's tail
RIBOSOMES:
1. Made of rRNA and proteins.
2.Made in the nucleolus
3. 2 subunits -one large (P and A), one small
4. Made separately and assembled in the cytosol
5. Free ribosomes or membrane bound (ER, nucleus, and mitochondria)
ENDOPLASMIC RETICULUM
l. extend from the nucleus to the plasma membrane
2. formed flattened sacs -cisterns
3. two types:
• Rough
-outer surface covered with ribosomes
-proteins enter RER for processing
-glycoproteins, or attached to phospholipids
• Smooth-extends from the RER -network of membrane tubules -does not synthesize
proteins -makes
phospholipids, steroids, fats -has specialized functions in some
tissues
*Liver -it releases glucose and detoxifies
*Muscle -releases calcium ions -triggers contraction.
GOLGI APPARATUS (COMPLEX)
1. Function : the packaging department
• Modifies proteins -i.e. glycoproteins etc.
• Packages them in membranes for various uses
2. Structure:
• Stack of flattened sacs with bulging edges =cistern)
• Cells usually only have one golgi complex
• Secretory cells have extensive golgi complexes
3. Process:
• Proteins arrive bound in a piece of ER membrane. -transport vesicle
• Transport vesicle fuses with the entry face
• Proteins are released into the cistern
• Proteins are modified by specific enzymes
• At the exit face the products are modified, sorted, and packaged in
another membrane. secretory vesicles
-take product to PM for exocytosis
-some are incorporated into the membrane
-storage vesicles leave and stay in the cytosol.
LYSOSOMES:
1. Function: digestion
-destroys old organelles
-autophagy
-recycles macromolecules
2. Hydrolytic enzymes
-acidic environment pH=S
MITOCHONDRIA
1. Function: production of ATP
-energy metabolism
• Krebs cycle
-in matrix
• Electron Transport
- inner membrane
• Cristae
-folds of the inner membrane
• Matrix granules
-stores and releases calcium ions.
2. Characteristics
• Self replicating
• Have their own DNA
-circular chromosome (more than one copy) -37 genes
-genetic traits come from mom only
-13 proteins for the mitochondria function
• 50 proteins to carry out respiration are coded for in the nucleus of the cell.
• Divide by fission- when energy requirement increases.
• Resemble purple bacteria
-theory that mitochondria were once parasitic bacteria.
• Number of mitochondria varies
-muscle cells and liver cells have a lot -lymphocytes have a few
NUCLEUS:
1. Function:
• "the control center of the cell"
-transcribes the DNA codes for proteins
• Heredity
- g e n e s
*control a specific characteristic -protein
*one gene, one protein
- c h r o m o s o m e s :
*genes are arranged in single file
*specific order on specific chromosomes
*46 in a human somatic cell (23 pairs)
2. Nuclear Structures:
• Nuclear membrane (envelope)
-lipid bilayer
-outer membrane continuous with ER
• Nuclear pores
-circular arrangement of proteins -large central channel
-lO X larger than channels in PM
• Nucleolus
-clusters of DNA, RNA, and protein
-assemble ribosomes
-disappear during mitosis
PEROXIOSOMES:
1. Function: oxidize organic substances
• Amino acids and fatty acids
• Toxic substances -i.e. alcohol
• Produce H202 as a byproduct
• Catalase decomposes the hydrogen peroxide
• Protects the cell from oxidative damage
• Self replicate
Clinical Applications:
1. Cystic Fibrosis:
• Genetic disorder
• Transport protein gets "stuck" in the ER or golgi complex
• Membrane lacks chloride ion transporter
• Ionic imbalance across the membrane
• Thick mucus builds up outside certain cells
-respiratory, digestive
2. Tay-Sachs
• Genetic disorder
• Lysosomal enzyme missing
• Breaks down ganglioside GM2 (found in nerve cells)
• Reactant accumulates due to lack of enzyme
• Nervous system damage results, death usually occurs before 5 years of age
REVIEW –CELL PROCESSES
REPLICATION
Definition: DNA makes a copy of itself
1. Function:
• cell division -growth (mitosis)
• cell reproduction
• production of gametes (egg and sperm)
• meiosis (reduction division)
2. Mechanisms:
• DNA unwinds
• Hydrogen bonds break
• DNA polymerase = enzyme
• New strand is synthesized next to the complementary strand.
• Each new DNA double helix is one old strand and one new strand.
• DNA polymerase proofreads the new strand.
• Chromatin
-diffuse granular mass in non-dividing cell
-beads on a string structure
*nucleosome =bead
*DNA wrapped 2X around 8 histones
*organize DNA
*string = linker DNA
-chromatin fiber = final folded DNA structure
THE CELL CYCLE
Definition: The sequence of events between cell divisions.
1. Stages of the cell cycle:
• Interphase
-non dividing cell
-important non-visible events
-stages of interphase
*GI = gap 1 –growth 2n
*GO =gap 0
-cells that don't divide (nerves)
*restriction point
-cell will divide once it reaches it
* S= Synthesis 4N
-DNA replication
*G2 = gap 2
4N
–cell prepares to divide
-protein synthesis of enzymes needed for mitosis
*M = Mitosis
-prophase
-metaphase
-anaphase
-telophase
PROTEIN SYNTHESIS
1. Transcription (rewrite) DNA code is rewritten into RNA
• Occurs in the nucleus
• DNA is unwound
• RNA polymerase (enzyme) attaches to the promoter (basically it says
"start here").
• DNA code is transcribed into the complementary code on the developing
RNA strand.
• Only one strand of DNA is used (the sense strand)
• Antisense strand is the one not transcribed.
• Terminator is the code sequence on DNA that tells RNA polymerase that it
is finished and it detaches.
• Newly transcribed mRNA contains both introns (non-coding regions) and
exons (regions that code for proteins).
• Pre-mRNA is modified by snRNPs (small nuclear ribonucleoproteins)
which cut out introns and connect exons into the functional mRNA
molecule that leaves the nucleus.
• What advantage is there making a mRNA that needs modification?
2. Translation -write in a new language (amino acids).
• Nucleotide sequence specifies amino acid sequence of a protein.
• mRNA goes to ribosome
• mRNA attaches to the small ribosomal subunit.
• Translation begins at the start codon (AUG), with the initiator tRNA.
• P site of the large subunit attaches to the small subunit is the binding site
for the initiator tRNA.
• A site is for the second tRNA.
• tRNA's are directed according to their anticodons to attach to the A site in the
appropriate order.
• Between the P and A site, amino acids attached to each tRNA form peptide
bonds.
• The tRNAs detach from both the ribosome and the amino acids as the peptide
chain forms.
• Ribosome shifts from codon to codon down the mRNA strand as the
polypeptide forms.
• Ribosome stops when it reaches the stop codon.
METABOLIC PATHWAYS:
Definition: Pathways are a series of chemical reactions required to achieve a specific
product.
• Reactions must occur in sequence
• Many times, reactions are reversible depending upon the amount of reactants
and product available
• Pathways may have points where other pathways conn ect.
• Check points in the pathway that control the amount of product are termed
limiting steps.
IMPORTANT BIOCHEMICAL PATHWAYS :
1. Glycolysis
-anaerobic catabolism of glucose to lactic acid.
-produces 2 ATP
-occurs in the cytosol
2.Aerobic Respiration -requires oxygen and mitochondria
-includes glycolysis
-Krebs cycle
-electron transport
-produces 38 ATP total
3. Protein synthesis
-mRNA transcription
-mRNA modification into functional strand -translation
4.Replication of DNA
-DNA makes a copy of itself for cell division