DNA and Replication Deoxyribonucleic Acid Chromosomes and DNA

DNA and Replication (Deoxyribonucleic Acid)

Chromosomes and DNA • Our genes are on our chromosomes. • Chromosomes are in the nucleus and made up of a chemical called DNA.

What is DNA’s Function? Located in the Nucleus • Hereditary Instructions • Chemical code for every trait • “Blueprint” for making Proteins

Why do we study DNA? DNA We study DNA for many reasons, e. g. , • Medical benefits such as cures for diseases. • (Gene Therapy) • Better food crops. • ( GMO’s -Genetically Modified Organisms). • Crime Scene Identification

Genetic material of cells… • GENES – units of genetic material that CODES FOR A SPECIFIC TRAIT • Called NUCLEIC ACIDS (DNA & RNA) • DNA is made up of repeating molecules called NUCLEOTIDES Nucleic acids: Many nucleotides linked in a long chain

DNA Nucleotide Basic structure of DNA is a sugar-phosphate backbone with 4 variable nitrogenous bases. This structure is called a nucleotide. Phosphate Group 5 P N O S C 4 Sugar (deoxyribose) C 3 C 1 C 2 Nitrogenous base (A, G, C, or T)

Four nitrogenous bases DNA has four different bases which are connected by hydrogen bonds C • Thymine T • Adenine A • Guanine G • Cytosine BALANCED 7

Chargaff’s Rule • Adenine must pair with Thymine • Guanine must pair with Cytosine • Their amounts in a given DNA molecule will be about the same T A G C

The Shape of the Molecule • DNA is a very long polymer. • The basic shape is like a twisted ladder • This is called a “double helix”. • With complementary base pairs (A-T, C-G) 9

DNA Molecule 10

Rosalind Franklin – Studied the structure of DNA USING X-Ray. She discovered that DNA is a helical structure. X-ray photo of DNA. Double Helix

Watson & Crick’s Model Watson and Crick – build the DNA molecule model from Franklin’s X-ray. Nobel Prize 1962

What is the correct complimentary DNA strand for the following CGTAAGC? A. GCATACG B. GCATTCG C. CCATTGC D. CGATACG 13

Which of the following codes for your traits? A. Sugars B. Nitrogen Bases C. Phosphates D. All of the above 14

What is the building block of a nucleic acid? A. Polymer B. Lipid C. Carbohydrate D. Nucleotide 15

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Vocabulary ü Replication – the process of DNA duplication ü Replication fork – Site where DNA strands separate and replication occurs. ü Enzyme – a protein that facilitates a specific chemical reaction in the body. ü Helicase: Unzips DNA strands ü DNA Polymerase: Joins nucleotides back together. Also, has proofreading function. Detects incorrectly paired nucleotides and corrects them.

Vocabulary ü Leading strand (5’ to 3’) – DNA strand that forms as a continuous strand during DNA replication. ü Lagging strand (3’ to 5’) – DNA strand that forms as a series of short segments, segments called Okazaki fragments, fragments which are then connected together. 18

What is DNA replication? q Happens in the nucleus q Happens during Interphase (S phase) q During DNA replication, the DNA molecule produces two new complementary strands. q Each strand of DNA serves as a template for the new strand. q Described as semiconservative because each DNA molecule has one new strand one original strand.

Steps of DNA Replication--- transcription--- translation 1. The two original strands of DNA are separated by helicase at the replication fork 2. DNA Polymerase adds complimentary nucleotides to each strand 3. Two DNA molecules from that are complementary, but identical to the original 20

Replication conserves genetic information - Each parent or original strand of DNA serves as a template this means the genetic information stays the same or is conserved.

DNA Replication 22

What did we learned? ü ü ü DNA, the genetic material of organisms, is composed of four kinds of nucleotides. Each nucleotide consists of a sugar, sugar a phosphate group and one of four bases ü Sugars and phosphates on the outside ü Nitrogenous bases paired by hydrogen bonds (A with T, T C with G) G The paired strands form a twisted-zipper shape called a double helix Before cell division, DNA copies itself in a process called replication During replication, DNA separates into two strands, strands and produces two new complementary strands following the rules of base pairing

What is the essential question? How does replication ensure that identical copies of DNA are made?

Genetic Diversity… • Different arrangements of NUCLEOTIDES in a nucleic acid (DNA) provides the key to DIVERSITY among living organisms.

The figure to the right shows which of the following? a. Translation b. Replication c. Transcription d. Protein Synthesis

Which choice describes DNA after replication has taken place? A. one molecule with two original strands and one molecule with two new strands B. two molecules, each with one original and one new strand C. two molecules, each with two new strands D. two molecules, each with two old strands

At what point in the cell cycle does DNA replication occur and why? A. before a cell divides, to provide each of the two resulting cells with a complete set of DNA instructions B. before a cell divides, to ensure that the DNA will fit into the resulting cells C. during cell division, to ensure that the DNA will fit into the resulting cells D. after a cell divides, to provide each of the two resulting cells with a complete set of DNA instructions.

Differences in DNA and RNA

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DNA Replication--- transcription--- translation • DNA is replicated in the nucleus. • DNA is transcribed into RNA in the nucleus • RNA is translated to protein in the cytoplasm 31

RNA types 1. Messenger RNA (m. RNA): copied from DNA, carries information from chromosomes to ribosomes. 2. Ribosomal RNA (r. RNA): make up ribosomes 3. Transfer RNA (t. RNA): transport amino acids to ribosomes

• Look at the figure below: What structure does this figure show? • A. DNA B. RNA • C. Protein • D Amino Acid

A. Cytoplasm B. Nucleus C. Ribosome D. Cell Membrane