Inquiry into Life Twelfth Edition

Cell Biology:DNALesson 1 DNA Replication (Inquiry into Life pg. 489-493)

Todays ObjectivesDescribe DNA Replication, including:Describe the three steps in the semi-conservative replication of DNA:unzipping (DNA helicase)Complementary base pairing (DNA polymerase)Joining of adjacent nucleotides (DNA polymerase)Describe the purpose of DNA replicationIdentify the site of DNA replication within the cellBackground informationIt is important to recall the information we learned about DNA from the last 2 units:DNA stands for deoxyribonucleic acidDNA is the molecule that makes up chromosomes and serves as hereditary information

Nucleic AcidsThere are two types of nucleic acids, DNA and RNABoth DNA and RNA are polymers of nucleotides (chains of joined nucleotides)They form genetic material and are involved in the functioning of chromosomes and protein synthesisDNA Structure:The shape of DNA is a double helix made up of repeating nucleotide units

Nucleotide StructureNucleotides are composed of 3 parts:1) phosphate molecule2) 5 carbon sugarDeoxyribose in DNARibose in RNA3) Nitrogen containing base

Nitrogen containing basesTwo types:Purines adenine (A) and guanine (G)Pyrmidines thymine (T), uracil (U) and cytosine (C)DNA has A,G,T,C, RNA has A,G,U,CPurines are larger than pyrimidines and have a double ring structure

Nitrogen containing basesPyrimidines are smaller than purines and have a single ring structure

When the bases bond together to form the rungs of the DNA ladder they do so in a set pattern. The alternating sugar and phosphates make up the rails (backbone). The bases make up the rungs.

Complementary Base PairingAdenine always bonds to thymineTwo hydrogen bondsGuanine always bonds to cytosineThree hydrogen bondsThis bonding of bases is called complementary base pairingThey cannot bond any other way because 2 purines would overlap and 2 pyrimidines would be too short to form the rungs of the ladderThe double strand is held in place by hydrogen bonds between the bases.It is the number and order as well as the type of the bases that determine what kind of organism will develop.

Order of BasesExample:ATCCGATT means something entirely different than ACCGTTAT, just as the words hate and heat mean different things even though they contain the same lettersAs a DNA strand lengthens, it twists into a double spiral called a double helixCandy DNA ModelNext class you will build a DNA molecule using CANDY! (you can eat it after you are finished)

DNA model .

Functions of DNA1) Replicates (duplicates) itself so each new cell has a complete, identical copy2) Controls the activities of a cell by producing proteinsThe combination of proteins determines the characteristics of each living organism3) Undergoes occasional mutations (mistakes in replication) which accounts for the variety of living things on earthDNA ReplicationCool website demonstrating the steps in DNA replicationhttp://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html

Steps in DNA Replication

1. The DNA molecule becomes untwisted by the enzyme DNA helicase breaking the H-bonds. The 2 strands that make up DNA become unzipped. Each side acts as a template. (ie. The weak hydrogen bonds between the paired bases are broken by an enzyme)

2.New complementary nucleotides, always present in the nucleus, move into place and pair with complementary bases on the exposed strands.

T joins to A

C joins to G

3. The adjacent nucleotides, through their sugar-phosphate components become joined together along the newly forming chain. The enzyme DNA polymerase helps this. (Adds nucleotides to template).

4. When the process is finished, 2 complete DNA molecules are present, identical to each other and to the original molecule.

5.Both DNA will now wind back up into their helical shape.DNA replication is called semi-conservative because each new double helix is composed of an old (parental) strand and a new (daughter) strand.Each strand conserves a length of the old strandEnzymes assist the unwinding process, join together the nucleotides, and assist the rewinding process and many others.When errors are made in replication. A mutation can arise.Meet the enzymes involved in DNA replicationDNA presentation