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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.

DNA Structure

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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. - PowerPoint PPT Presentation

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Page 1: DNA Structure

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.

Page 2: DNA Structure

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

Page 3: DNA Structure

From DNA to Protein

Page 4: DNA Structure

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

Page 5: DNA Structure

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. •

Page 6: DNA Structure

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)

Page 7: DNA Structure

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)

Page 8: DNA Structure

Overview of Transcription

Page 9: DNA Structure

• mRNA leaves the nucleus via a nuclear pore and travels to a ribosome that is attached to the ER or free in the cytoplasm.

Page 10: DNA Structure

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)

Page 11: DNA Structure

DNA and Peptide Formation

Page 12: DNA Structure

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.

Page 13: DNA Structure

Cell Cycle

Page 14: DNA Structure

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.

Page 15: DNA Structure

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

Page 16: DNA Structure

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

Page 17: DNA Structure

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)

Page 18: DNA Structure

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

Page 19: DNA Structure

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

Page 20: DNA Structure

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

Page 21: DNA Structure

Prophase

Page 22: DNA Structure

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.

Page 23: DNA Structure

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

Page 24: DNA Structure

Daughter chromosomes

Anaphase

Anaphase

Page 25: DNA Structure

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.

Page 26: DNA Structure

Telophase and Cytokinesis

Telophase and cytokinesis

Nucleolus forming

Contractile ring at cleavage furrow

Nuclear envelope forming

Page 27: DNA Structure
Page 28: DNA Structure

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