2What I need to know:-DNA units are called nucleotidesA nucleotide consists of a deoxyribose sugar, phosphate and baseThere are four bases (cytosine, guanine, adenine and thymine). These bases have complimentary base pairings which are joined by hydrogen bondsStrong chemical bonds form between nucleotides to make a strand of DNATwo DNA strands run anti-parallel to each other and twist into a double helixDNA is arranged so that it tightly coils into a chromosome
3DNADo you remember what DNA stands for? Where is it found? What does it code for?
4DNAEach molecule of DNA consists of 2 strands, where each strand is made up of repeating units called NUCLEOTIDES.The nucleotide is made of :Deoxyribose sugarPhosphateOrganic Base
6NucleotideThere are 4 different types of nucleotides. This is because there are 4 different bases: GUANINE CYTOSINE THYMINE ADENINE
7Complementary base pairing Each base can only join with one other base. 4 bases:ThymineAdenineCytosineGuanineThis is always the case in DNA – G-C, T-A pairs
8STRONG CHEMICAL BOND links the nucleotides between the phosphate and sugar. They are not easily broken and join nucleotides together into a permanent strandADENINEGUANINE
9The 2 strands are arranged in a twisted coil called a “DOUBLE HELIX” The 2 strands are arranged in a twisted coil called a “DOUBLE HELIX”. It is often likened to a spiral ladder, where the sugar-phosphate backbone is the railing and the base are the stepsADENINETHYMINEGUANINECYTOSINEWeak hydrogen bond
10Notice how the two strands run anti-parallel to each other 5’3’ADENINETHYMINEGUANINECYTOSINENotice how the two strands run anti-parallel to each other3’5’
12Arrangement of DNADNA is tightly coiled and found on chromosomes If you take the DNA from one cell it would stretch out to 2 meters! Therefore it is essential that the DNA is arranged so that it fits within the nucleus of a cell It is tightly coiled and packaged around bundles of protein (like beads on a string)
13Now attempt the following questions How many different types of base molecules are found in DNA? Name each type.Which type of bond forms between the bases of adjacent strands of a DNA molecule?Describe the base pairing ruleDraw the complementary strand for the following strand or DNAC A T G C C A T G T A G5’3’
145) What term is used to describe the two strands of DNA that run in opposite directions 6)What name is given to the twisted coil arrangement typical of a DNA molecule?7) If DNA is like a spiral ladder, which part of it corresponds to the ladder’s (i) rungs (ii)uprights?
15GlossaryCOMPLEMENTARY – fitting together like a hand in a glove; applied to DNA base pairingDOUBLE-STRANDED HELIX – describes the spiral ladder shape of DNA moleculesNUCLEOTIDE – unit which consists of a ribose or deoxyribose sugar joined to a phosphate group and to an organic base