Planet Earth and Its Environment A 5000-million year Journey

Biology in Focus, HSC CourseGlenda Childrawi, Margaret Robson and Stephanie Hollis

Blueprint of LifeTopic 17: DNA Functioning 1DOT POINT(s)describe the process of DNA replication and explain its significanceIntroduction The discovery of the biochemical detail of the structure of DNA by Watson and Crick in 1953 (12 years after Beadle and Tatums work) brought about a better understanding of the biochemical functioning of DNA. www.nobelweekdialogue.org

Introduction Besides storing and transmitting all the heredity information in every cell of an individual, DNA plays an active role in gene expression, central to cell functioning and determining the phenotype of living organisms.five30liveservice.wordpress.com

Introduction The active functioning of DNA in the everyday activities of cells takes two forms:1. DNA replication: in its hereditary role, DNA must be able to make an exact copy of itself so that when a cell divides, the resulting daughter cells each have a full complement of DNA.www.sciencesuperschool.com

Introduction 2. protein synthesis: genes are expressed in terms of the protein products that they produce. Many of these proteins are enzymes, which control chemical functioning of cells. DNA directs the production of these proteins.

culturingscience.wordpress.com Introduction Other proteins produced may form a structural part of the cell (e.g. the protein in cell membranes, pigment in skin and eyes, and silk in insect cocoons) and some proteins form essential chemicals such as hormones (e.g. insulin), defence proteins (e.g. antibodies) and transport proteins (e.g. haemoglobin).theelephantman.deviantart.com

DNA ReplicationDNA replication is the production of two identical double stranded molecules of DNA from one original double helix molecule. The process of DNA replication in cells is termed semiconservative, as the two strands of the original DNA molecule separate and each gives rise to a new complementary strand.

sharonchoi-sbi4u.blogspot.com DNA ReplicationThis mechanism ensures that the genetic material is copied exactly. DNA replicates before cell division so that each cell can receive one full and exact copy of the coded instructions that control the basic life functions of the cell.bio4esobil2010.wordpress.com

DNA ReplicationWhen Watson and Crick discovered the structure of DNA, they noted immediately that their model suggested a possible copying mechanism for the genetic materialif the strands separated, each could act as a template for the synthesis of a new, complementary strand and this is indeed what happens.alevelnotes.com

The ProcessThe process of DNA replication occurs in three steps:1. The DNA double helix unwinds. Each DNA molecule is a double stranded helix. An enzyme called helicase causes the DNA helix to progressively unwind.www.nist.gov

The Process2. DNA unzips that is, the two strands separate. The weak hydrogen bonds break between the complementary bases of the nucleotides on opposite strands and the two DNA strands separate, exposing the nucleotide bases.pinterest.com

The ProcessIf you think of DNA as a ladder, each rung splits down the middle, creating a replication forkbeyond this point, the DNA resembles a flat ladder where the sides are made up of a sugarphosphate backbone and the rungs are formed by complementary base pairs.truthfall.com

The Process3. Nucleotides are added to each single strand:Each separate strand of the existing DNA molecule acts as a template for the production of a new strand of DNA. Nucleotides (units made of sugar phosphatebase) are picked up by the enzyme DNA polymerase and slotted in opposite their complementary base partner on each of the existing strands. www.personal.psu.edu

The ProcessThese nucleotides are picked up from a pool of nucleotides in the nuclear sap. Nucleotide pairing is specific. Adenine (A) always pairs with thymine (T) nucleotides. Guanine (G) always pairs with cytosine (C) nucleotides.www.bcscience.com

The ProcessThe direction in which nucleotide insertion occurs is antiparallel on the two opposite strandson one strand it begins at the replication fork and goes towards the end of the strand, whereas on the other strand it begins at the end of the single strand and goes towards the replication fork. www.scienceprofonline.com

The ProcessThe base pairing is checked by another DNA polymerase enzyme which edits any incorrect additions, to ensure accuracy. Incorrect base pairing will result in a change in the DNA base sequence, known as a mutation.

www.rationalresponders.com Result of DNA ReplicationEach resulting DNA molecule contains one strand of the existing DNA molecule and a newly-synthesised strand. The replicated DNA molecules rewind into the double helix conformation, like the original molecule. vinodwadhawan.blogspot.com

Result of DNA ReplicationThe end result is that there are two molecules of DNA, each a double-stranded helix, and they are identical to each other and to the original molecule from which they formed.library.thinkquest.org

The Significance of DNA ReplicationThe genetic material of a cell must be transmitted from: one cell to another during mitosis, allowing for growth and repair and maintenance of an organism one generation to another during meiosis (e.g. when gametes are formed for sexual reproduction).www.biologyjunction.com

The Significance of DNA ReplicationIn each of these situations, it is necessary for the DNA to make an exact copy of itselfthat is, DNA replication occurs. Replication of DNA ensures that the genetic code of a cell is passed on to each new daughter cell that arises from it. An exact replica or copy of the DNA must be produced so that the new cells have the same, distinctive message that the original cell had. If DNA replication goes wrong, this has a direct effect on the phenotype of the individual.www.biomedcentral.com

Activity/Homework-Students to watch DNA Replication Video:http://youtu.be/FBmO_rmXxIw

If time watch:http://youtu.be/zFVH9SqtJCM

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