STRUCTURE OF DNA TOPIC 1 - 2015

YEAR 10 BIOLOGY Topics Structure of DNA Chromosomes & Cell division Genetics & Inheritance Theory of Evolution Evidence for Evolution

YEAR 10 BIOLOGY Assessment Evolution poster Genetics prac report Unit test End of semester examination and various worksheets / quizzes throughout the course...

STRUCTURE OF DNA Things to cover History Location Components Base pairing Shape

HISTORY OF DNA

HISTORY OF DNA 1869 DNA was discovered by Friedrich Miescher His team isolated it from pus on bandages! He called their discovery nuclein.

HISTORY OF DNA 1929 Phoebus Levene determined that the compound had a repeating structure. He called these repeated units nucleotides. He also suggested that these units link together to form chains. His theory was correct, but his prediction about the way the chains formed was not.

HISTORY OF DNA 1943-1953 Oswald Avery , and Alfred Hershey and Martha Chase made the suggestion that this compound was capable of transferring genetic information between generations

HISTORY OF DNA 1950 Erwin Chargaff determined that there were four types of nucleotides that paired up within the structure of DNA This is known as Chargaff’s rule or the base pairing rule.

HISTORY OF DNA 1953 Rosalind Franklin came very close to solving the DNA structure She made xray crystallographic portraits of DNA in order to try to determine its 3D structure. Source: www.makingthemodernworld.org.uk

HISTORY OF DNA 1953 Her work was given without her consent to a group of scientists in another laboratory by her colleague, Maurice Wilkins. Source: www.makingthemodernworld.org.uk

HISTORY OF DNA 1953 James Watson and Francis Crick made a model of DNA that incorporated the findings of Chargaff, Franklin and Wilkins. Their model fit the experiential data so perfectly that it was almost immediately accepted. Source: tokresource.org

HISTORY OF DNA 1962 JOHN STEINBECK WILKINS CRICK WATSON Watson, Crick, and Wilkins won the Nobel Prize for physiology/ medicine. Rosalind Franklin had died of cancer in 1956. Source: achievement.org

HISTORY OF DNA 1962 The Nobel Prize only goes to living recipients, and can only be shared among three winners. Were she alive, do you think she would have been included in the prize? Source: omniscienceblog.com

LOCATION OF DNA

LOCATION OF DNA DNA is a chemical located in the nucleus of every living cell. NUCLEUS DNA

LOCATION OF DNA It is a nucleic acid. Its full name is deoxyribonucleic acid. Its role is to store coded instructions about how to make proteins. In this way, it directs cell division, growth & function.

COMPONENTS OF DNA

COMPONENTS OF DNA DNA is a large molecule made up of smaller sub-units called nucleotides Each nucleotide consists of: a nitrogenous base a pentose sugar a phosphate group There are four different DNA nucleotides

COMPONENTS OF DNA Pentose sugars There are two sugars that are used in nucleotides: deoxyribose sugar  used in DNA ribose sugar  used in RNA

COMPONENTS OF DNA Nitrogen bases There are four nitrogen bases in DNA: A = Adenine T = Thymine G = Guanine C = Cytosine There is a fifth nitrogen base found only in RNA: U = Uracil

COMPONENTS OF DNA Chemical bonds The three components are held together by covalent bonds. These bonds are strong so that the unit holds together within the larger molecule. COVALENT BOND COVALENT BOND

CHARGAFF’S BASE PAIRING RULE

BASE PAIRING IN DNA C G A T The nitrogen bases exhibit complementary base pairing. This means that each base only join with one other base: Adenine joins with Thymine (A=T) Guanine joins with Cytosine (C≡G) C G A T

BASE PAIRING IN DNA Reasons behind the rule: Size of bases Number of hydrogen bonding sites

SHAPE OF DNA

SHAPE OF DNA DNA is double stranded. Each strand is made up of nucleotides, connected through chemical bonds. These two strands are twisted around each other. This is called a double helix.

SHAPE OF DNA The structure is similar to a twisted ladder. The “rungs” of the ladder are made from the complementary nitrogen base pairs. The “sides” of the ladder are made from alternating sugar and phosphate groups. This is called the sugar-phosphate backbone.

C G A T COMPLEMENTARY NITROGEN BASE PAIRS SUGAR-PHOSPHATE BACKBONE

SHAPE OF DNA The nucleotides are joined by covalent bonds  these are very strong The two strands are joined by hydrogen bonds  these are very weak, This allows the strands to be separated during DNA replication and protein synthesis without destroying the DNA completely

COVALENTBONDS HYDROGEN BONDS C G A T