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Physiology 1
LECTURE 3 NOTES
By Dr. Tom Madayag
Genetic Control of Protein Synthesis, Cell Function, and Cell Reproduction
https://www.youtube.com/watch?v=zwibgNGe4aY
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Genes in the cell nucleus control protein synthesis
Genes are attached in a double stranded helix
Basic building blocks of DNA
https://www.youtube.com/watch?v=1YDTOcAVJrE
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Nucleotides
o Organized to form two strands of DNA
o Ten pairs of nucleotides are present in each full turn of the helix
o Components
1. Phosphoric acid
2. Sugar called deoxyribose
3. Four nitrogenous bases
 Adenine
PURINES
 Guanine
 Thymine
Pyrimidines
 Cytosine
4. Hydrogen bonds hold two respective DNA strands
Each purine base always bonds with a pyrimidine base
1. ADENINE TO THYMINE
2. GUANINE TO CYTOSINE
3. Remember: Apple to Tree; Car to Garage
Genetic Code
o IF DNA is split, purine & pyrimidine project to each side
o These projecting bases form the genetic code
o Genetic code consist of triplets of bases
o The DNA code in the cell nucleus is transferred to the RNA code in the cell cytoplasm in
the process called transcription
o The RNA in turn diffuses to the cytoplasmic compartment where it controls protein
synthesis
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https://www.youtube.com/watch?v=zFVH9SqtJCM
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 RNA is synthesized in the Nucleus from a DNA Template
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The two strands of the DNA molecule separate temporarily
The code triplets in the DNA cause formation of complimentary code triplets
(CODONES) in the RNA
o Codons control the sequence of amino acids to be synthesized in the cell cytoplasm
Basic Building Blocks of RNA
o Same as DNA except
1. Sugar deoxyribose not used. Instead Ribose is used
2. Thymine is replaced by Uracil
Formation of RNA Nucleotides
o Same as in DNA
o Adenine, Guanine
o Cytosine, Uracil
Activation of the RNA Nucleotides
o Enzyme RNA polymerase
Transcription
https://www.youtube.com/watch?v=pNVPB6NFIZU
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In the DNA strand immediately ahead of the gene to be transferred is the PROMOTER
The RNA polymerase attaches to the promoter; causes unwinding and separating of the
two strands
When the RNA polymerase encounters the chain-terminating sequence, RNA and
polymerase separate from the DNA strand
1. DNA rebinds with its complimentary strand
2. RNA chain forced away from the DNA an released to nucleoplasm
Different types of RNA
1. Precursor messenger RNA (pre-mRNA) - immature single strand RNA. Contains
introns (removed by process called splicing) and exons (retained in the final
RNA)
2. Small nuclear RNA (snRNA) – directs the splicing of pre-mRNA to form mRNA
3. Messenger RNA (mRNA)) carries the genetic code to the cytoplasm
4. Transfer RNA (tRNA)- transports activated amino acids to the ribosomes to be
used in assembling the protein molecule. Contains anticodons
5. Ribosomal RNA- form ribosomes (where protein molecules are actually
assembled)
6. Micro RNA (miRNA)- single stranded RNA molecules of 21 to 23 nucleotides that
can regulate gene transcription and translation
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Translation
https://www.youtube.com/watch?v=8dsTvBaUMvw
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Formation of proteins on the ribosomes
Ribosome “reads” the codons
CELL REPRODUCTION
https://www.youtube.com/watch?v=JcZQkmooyPk
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 Begins with replication (duplication) of DNA
 These replicas become the DNA in the two new daughter cells
 DNA nucleotides are “proof-read”; when a mistake is made—mutation
Chromosomes & their Replication
 Human cell contains 46 chromosomes, arranged in 23 pairs
 Protein HISTONES packages DNA tightly
 Newly formed chromosomes attached at a point called centromeres
 The duplicated but still attached chromosomes are called chromatids
Cell Mitosis
 Process by which the cell splits into two
 Steps: Shortly before mitosis, two pairs of centrioles begin to move apart from each
other forming spiny star-shape (ASTER). Some spines penetrate the nuclear membrane.
Together with the spindle, they form the mitotic apparatus.
1. Prophase
 Spindle is forming
 Chromosomes become condensed into well-defined chromosomes
 Pro-metaphase
o Fragmentation of the nuclear membrane
o Microtubules from aster attach to chromatids at center
o Tubules pull one chromatid toward cellular pole and partner to
opposite pole
2. Metaphase
 Actin slides the spines in a reverse direction along each other
 Chromatids pulled to form the equatorial plate
 Remember this stage by thinking of M as in middle
3. Anaphase
 Two chromatids of each chromosome are pulled apart at the
centromere
 The 46 pairs of chromatids are separated forming two separate sets of
46 daughter chromosomes
 Remember this stage by remembering A representing AWAY
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4. Telophase
 Two sets of daughter chromosomes are pushed completely apart
 Mitotic apparatus dissolves
 New nuclear membrane develops around each set of chromosomes
 Cell pinches in two caused by formation of aa contractile ring
(composed of actin and myosin)
 Remember this stage by remembering T representing TWO
Control of Cell Growth and Cell Reproduction
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Some cells reproduce all the time (blood-forming cells of bone marrow, skin)
Some cells do not reproduce (except during fetal life)
o Neurons
o Most striated muscle cells
Insufficiency of some cells cause them to grow
o Example: liver--- transplant
Control of cell growth
o Growth factors
o Contact inhibition- stop growing when there I no space
o When own secretions of the cells collect (negative feedback control)
Telomeres
o Region of repetitive nucleotide sequences at each end of a chromatid
o Serve as protective caps that prevent chromosome from deteriorating during cell
division
o With each cell division, the copied DNA loses nucleotides at the telomere region
o Explanation of aging
o Telomere erosion can also be caused by diseases
o Telomerase activity adds bases to allow more generations of cells can be produced
(stem cells of bone marrow, skin)
Apoptosis
o Programmed cell death
o When cells are no longer needed or become a threat to the organism
 Cancer
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Caused by mutation or by abnormal activation of cellular genes that control cell growth
and cell mitosis
Proto-oncogenes—normal genes
Oncogenes- cancer causing
anti-oncogenes (tumor suppressor genes)- suppresses activation of specific oncogenes
What causes mutations
 Ionizing radiation
 Chemical substances
 Physical irritants
 Heredity tendency
 Certain viruses
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Invasive Characteristics of the Cancer Cell
 Does not respect usual cellular growth limits
 Far less adhesive to one another
 Angiogenesis: formation of new blood vessels supplies nutrients
https://www.youtube.com/watch?v=8LhQllh46yI