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 facilitates base pairing

– mRNA 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 (anti-codons) 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

Centromere

Chromosome, consisting of two sister chromatids

Fragments of nuclear envelope

Late prophaseEarly prophase

Spindle pole

Kinetochore microtubule

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

Daughter chromosomes

Anaphase

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

Telophase and cytokinesis

Nucleolus forming

Contractile ring at cleavage furrow

Nuclear envelope forming

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