Transcript Bio_130_files/Cellular Function_1

DNA Structure
• DNA functions as the blueprint that will drive all
cellular activities.
– When a cell divides it is critical that each cell has identical
DNA.
Gene Expression
• DNA serves as a blueprint for actions of the cell.
– Its like a football team’s playbook.
• Specific segments of the DNA code for different
amino acids.
– This allows for reproducible instructions for a
specific polypeptide.
• Production of proteins provide a means of
expression of the genetic code.
– Every 3 nucleotides of a gene forms a (Triplet)
– Each triplet specifies coding for an amino acid
From DNA to Protein
Overview of Protein Synthesis
• DNA directs the synthesis of all cellular activities
– Is confined to the nucleus therefore it must use a
messenger.
– Proteins including enzymes regulate metabolic functions
and direct the synthesis of nonproteins
• Transcription ( DNA
RNA )
– Complimentary base pairing of DNA to form the
messenger RNA (mRNA) results in a series of codons
– mRNA migrates out of the nucleus to a ribosome in the
cytoplasm
• Translation (RNA
Protein )
– mRNA (codon) is complimented on ribosome by
Transfer RNAs (tRNA’s) which transfers amino acids to
the ribosome
– amino acids are assembled into a protein molecule
Genetic Code
• System that enables the 4 nucleotides (A,T,G,C) to code for
the 20 amino acids
• Base triplet: found on DNA molecule (ex. TAC) and will
code for 1 amino acid
• Codon: (mRNA)
– “mirror-image” sequence of nucleotides found in mRNA
(ex AUG)
– 64 possible codons (43)
• often 2-3 codons represent the same amino acid
• start codon = AUG
• 3 stop codons = UAG, UGA, UAA
• AntiCodon: (tRNA)
– Compliment the mRNA (AUG)
(UAC) brings a
specific protein to the ribosome.
•
Transcription
DNA to mRNA
– RNA polymerase binds to DNA
• at site selected by chemical messengers from
cytoplasm
• Breaks H-bonds separating and unwinds DNA helix
• Complementary base pairing of DNA to form new
strand of mRNA
– C on DNA,
G to mRNA
– A on DNA,
U to mRNA, ( No T in RNA)
Transcription
– DNA
TAC ACC CCG GGC AAT
RNA polymerase
– mRNA
facilitates base pairing
AUG UGG GGC CCG UUA
– Start codon ( Initiates protein synthesis)
– stop codon
(signals the end of the protein)
Overview of Transcription
• mRNA leaves the nucleus via a nuclear pore and travels to
a ribosome that is attached to the ER or free in the
cytoplasm.
Translation (Protein Synthesis)
• Protein molecules are created
on the ribosome.
• A ribosome unites the codons
of mRNA and tRNA’s (anticodons) to assemble the
primary structure of a protein
• Amino acids are brought to the
ribosome by transfer RNA
(tRNA)
DNA and Peptide Formation
Genetic Code
• RNA codons code for amino
acids according to a genetic code
• Some codons may code for
different amino acids.
• Non Sense Mutations
– Change in amino acid results
in the formation of a stop
codon resulting in a shorter
protein.
• Overt mutation:
– A change in the genetic code
that codes for a new amino
acid
• Silent mutation:
– codes for the same amino
acid.
Cell Cycle
Cell Cycle
• Cell cycle
– all the of events in the life of a cell
• Cells are constantly replacing old ones or adding to
the number of cells already present through a process
called mitosis (cell division)
• Some cells have very long cell cycles. The neuron has
to last for the rest of your life.
– Does alcohol kills brain cells?
• Some cells are constantly replacing themselves.
• Short cell cycle.
– Skin cells are constantly replacing the old cells.
• Most of the dust in the air is old dead skin cells.
Interphase
• 90 % of life cycle is devoted to prepare the cell to divide.
• First gap phase (G1)
– Growth: makes many of the proteins needed growth and
metabolic demands.
• Synthesis (S)
– DNA replication occurs
• the original 46 molecules of DNA is doubled to form an
identical copy resulting in 92 molecules of DNA
– Copies of DNA appears in a long delicate form called chromatin.
• Second gap phase (G2)
– Continued growth
– Synthesis of enzymes that control cell division.
– Final preparation for Mitosis
DNA Replication
• DNA forms from a preexisting strand (semi-conservative
replication)
• Steps of replication process
– DNA helicase opens short segment of helix
• replication fork is point of separation of 2 strands
– DNA polymerase assembles new strand of DNA next to one of
the old strands
• 2 DNA polymerase enzymes at work simultaneously
DNA Replication
• Law of complimentary base pairing allows
building of one DNA strand based on the
bases in 2nd strand
• ATC CCG GGC AAT GGT CCC
• DNA polymerase
• TAG GGC CCG TTA CCA GGG
• Complimentary strand
(Triplets)
Mitosis
• Essential for body growth and tissue repair
– Mitosis produces 2 genetically identical
daughter cells as the parent cell.
• Cytokinesis – division of the cytoplasm
• The phases of mitosis are:
– Prophase
– Metaphase
– Anaphase
– Telophase
Prophase
DNA in the form of chromatin produced
during S-phase begins to coil and
condense into sister chromatids.
Identical DNA molecules are connected
by a centromere.
Nuclear envelope dissolves allowing the
chromosomes to be released into the
cytoplasm.
Centrioles migrate towards opposite
sides of the cell
Prophase
Early mitotic spindle
Pair of centrioles
Fragments of
nuclear
envelope
Centromere
Kinetochore
microtubule
Spindle pole
Chromosome, consisting of two sister chromatids
Early prophase
Late prophase
Prophase
Metaphase
• Chromosomes cluster at
the middle of the cell
with their centromeres
aligned at the exact
center or equator of the
cell
– the metaphase plate
• Spindle fibers from each
centriole attach to the
kinetochores of the
centromere.
Anaphase
• Centromeres of the
chromosomes split
and spindle fibers pull
sister chromatids
toward opposite poles
of the cell.
• Each daughter cell
now has 46
molecules of DNA
Anaphase
Daughter chromosomes
Anaphase
Telophase and Cytokinesis
• New sets of chromosomes
extend into chromatin
• New nuclear membrane is
formed from the rough ER which
will form a new nucleus for the
new chromatin.
– A new nucleoli reappears
• Cytokinesis (cell division)
• The cell’s cytoplasm forms a
cleavage furrow splitting the cell
into two.
– begins in late anaphase and
finished in telophase.
Telophase and Cytokinesis
Nucleolus
forming
Contractile
ring at
cleavage
furrow
Nuclear
envelope
forming
Telophase and cytokinesis
Cancer
• Tumors (neoplasms)
– abnormal growth, cells multiply faster than they
die
– oncology = study of tumors
• Benign
– connective tissue capsule, slow growth, stays
local
– potentially lethal by compression of vital tissues
• Malignant tumor = cancer
– unencapsulated, fast growing, metastatic
(spreading), stimulate angiogenesis