PAP Biology DNA What are nucleic acids? Why is DNA important? Structure of DNA Scientists

Review What are the two types of nucleic acids? _________________ & _______________ Is a nucleic acid a monomer or polymer? __________________________ What is the monomer of DNA and RNA? _________________________ DNA RNA POLYMER nucleotide

Understanding DNA video (6 min)

Summary of Scientists Griffith— Avery— Hershey & Chase— Chargaff— Wilkins & Franklin— Watson & Crick— discovered genetic transformation of bacteria discovered DNA is genetic material confirmed DNA is genetic material discovered nitrogen base pairing rules developed X-ray pictures of DNA discovered shape/structure of DNA

DNA The Master Molecule video (stop at 5:50)

DNA Location DNA stands for deoxyribonucleic acid Location: DNA is found in the nucleus of eukaryotic organisms like plants, animals, protists and fungi In prokaryotic organisms (like bacteria) that do not have a nucleus, DNA can be found in a single circular chromosome within the cell

DNA Function Function: DNA stores and carries the information that is passed from one organism to its offspring (from parent to child)

What is DNA? The information is coded in the order of the nucleotide bases (the monomers) The monomer of DNA is made of: Phosphate group 5 carbon sugar (deoxyribose) Nitrogen containing base These three components make up the monomer called a nucleotide

Nucleotide

Why is DNA Important? DNA is in all living things DNA is the informational code that makes each organism unique.

The Structure of DNA double helix- two strands of nucleotides twisted around each other, like a winding staircase there is a “right side up” strand and an “upside down” strand. this arrangement of 2 strands running side by side but in opposite directions is described as antiparallel

The Structure of DNA Nucleotides- subunits (monomers) that make up DNA composed of: Phosphate group 5- carbon sugar (deoxyribose in DNA) Nitrogen containing base: The bases pair in the same way in every DNA molecule, we call this complementary base pairing Adenine Thymine (A – T) Guanine Cytosine (G – C) * Weak hydrogen bonds hold bases together

Base Pairs We refer to adenine, thymine, cytosine and guanine as the nitrogen bases or just “bases” So, when you say “a sugar, a phosphate and a base” you are implying that the base is either adenine, thymine, guanine or cytosine

Base Pairs The order of the base pairs provides that “unique code” that makes us all different. GTAACTTAG does not contain the same information as GGACAATTT even though both sequences contain the same nucleotides However, if the nucleotide sequences of nitrogenous bases (adenine, guanine, cytosine, thymine) are in a similar order, the two organisms are closely related This concept is used in forensic science and is called DNA fingerprinting

Label complementary bases and draw the appropriate number of hydrogen bonds 

The Structure of DNA *Note about bases: Pyrimidines- single ring of carbon Thymine and Cytosine Purine- two rings of carbon Adenine and Guanine A purine must always hydrogen bond with a pyrimidine!

Label all hydrogen bonds with an H 3’ P T H A S Label: Phosphate (P) 5 carbon sugar (S) - Correct base pairs (A, T, C, G) Label all hydrogen bonds with an H -Label the 5’ and 3’ ends Circle a nucleotide T A C G T A G C T A 5’

DNA Review What does DNA store that is important? If a DNA strand read 3’ AGT-CCG-GTA 5’ what would the complementary strand read? What holds the nitrogen bases together? What are the 3 components of a nucleotide? Genetic information in its sequence of nitrogen bases 5’ TCA-GGC-CAT 3’ Hydrogen bonds Sugar, phosphate group, and nitrogen base

1 DNA molecule  2 identical DNA molecules DNA Replication DNA replication- the process of making a copy of DNA 1 DNA molecule  2 identical DNA molecules Why is this important? cells need to copy their DNA before the cells divide in mitosis (growth, repair, and maintenance) Where does DNA replication occur? in the nucleus (because DNA is found in the nucleus in eukaryotic cells)

DNA Replication Summary of what we will learn There are three steps to DNA replication: 1) helicase unwinds the double helix opens the strand by breaking the hydrogen bonds between the bases 2) DNA polymerases add nucleotides in a 5’ to 3’ direction, moving TOWARD the replication fork; The leading strand is built quickly and the lagging strand is built more slowly in short 5’ to 3’ segments. 3) DNA polymerases detach once replication is complete and you end with 2 identical molecules of DNA, each made of one old strand and one new strand

DNA Replication Step 1: the double helix must unwind before replication can begin. then the DNA “unzips” DNA helicase is an enzyme that opens the double helix by breaking the hydrogen bonds that hold the complementary bases together (think of a zipper) enzymes end in (-ase)

DNA Replication Step 1 con’t: once separated, additional proteins hold the strands apart the place where the double helix splits is called the replication fork (it’s Y-shaped)

DNA Replication Step 2: at the replication fork, enzymes called DNA polymerases move along each of the DNA strands DNA polymerases add nucleotides to the 3’ end exposed bases according to the base pairing rules

DNA Replication The overall direction of adding nucleotides is toward the replication fork goes from 5’ to 3’

One strand, called the leading strand, grows quickly in the 5’ – 3’ direction toward the replication fork. The other strand, called the lagging strandis created next to the 3’5’ strand. It must add nucleotides in short 5’3’ segments (called Okasaki fragments), but goes slowly since it has to wait for it to unzip then fill in backwards a little section at a time making it “grow” in the wrong direction (away from the replication fork). These fragments are joined by ligase. Ultimately the overall direction of “growth” is toward the replication fork, but must be done in small segments filling in away from the fork.

DNA Replication Step 3: step 2 continues until all DNA has been copied and the polymerases detach produces 2 DNA molecules that are identical to each other

DNA Replication is semiconservative semi – half conserve – to save

DNA Replication Semiconservative: This means that every double stranded molecule of DNA has one strand that is from the “old” DNA and one strand is “new”

Summary DNA unwinds & unzips using helicase DNA polymerases add nucleotides to the 3’ end of the strands, moving toward the replication fork (5’  3’) 2 new strands of DNA are made that are identical to the original strands and to each other The process is semiconservative