1.5 - nucleic acids - garlick

DNA

deoxyribonucleic acid

codes for the sequence of amino acids in the primary structure of a protein, which in turn determines the final 3D structure and function of a protein.

contains the genetic code and can be passed on to make new cells and passed on to the next generation.

DNA is a polymer - and two polymer chains join together to create a double helix

DNA nucleotide

monomer that makes up DNA is called nucleotide.

made up of deoxyribose (pentose sugar), a nitrogenous base and one phosphate group.

nitrogenous group can either be guanine, cytosine, adenine and thymine.

Have to mention the pentose sugar and nitrogenous base that is relevant to DNA

polynucleotides

polymer of nucleotides is called a polynucleotide

created via condensation reactions between the deoxyribose sugar and the phosphate group (of another nucelotide), creating a phosphodiester bond, water is removed - makes sugar phosphate back bone very strong from the phosphodiester bond its a strong covalent bond.

DNA polymer occurs in pairs joined by hydrogen bonds between complementary base pairs. this creates the double helix.

hydrogen bonds can only from between complementary base pairs

• cytosine and guanine (CG)

• adenine and thymine (AT)

RNA

another nucleic acid

RNA is a polymer of a nucleotide formed of ribose, nitrogenous base and phosphate group

pentose sugar is = RIBOSE

nitrogenous bases = adenine, guanine, cytosine and uracil

doesn’t have thymine

RNA is much shorter polynucleotide than DNA polynucleotide - this is because mRNA is only a copy of one gene whereas DNA is all of the genes. tRNA are relatively short also

all of the polymers are single stranded for RNA

rRNA

the function of RNA is to transfer the genetic code from DNA in the nucleus to the ribosomes. Some RNA (rRNA) is also combined with proteins to make ribosomes

DNA replication

before cells divide (by mitosis or meiosis) all the DNA (genome) must replicate to provide a copy for the new cell

this process of DNA replication is semi conservative replication

(in the daughter DNA one strand is from the paternal DNA and one strand is newly synthesised strand to create new molecule)

semi conservative replication

step 1 - Enzyme DNA helicase breaks hydrogen bonds between the complementary base pairs between the two strands within a double helix - this causes the DNA double helix to unwind and the strands separate.

step 2 - both of these strands will act as a template

free floating nucleotides within the nucleus will align opposite their complementary base pairs (are attracted to) on the template strands of the parental DNA

step 3 - Enzyme DNA polymerase will join adjacent nucleotides together which then from phosphodiester bonds by a condensation reaction

(DNA polymerase catalyses the joining together of adjacent nucleotides)

step 4 - One strand of rental (original) DNA and one newly syntheisised strand are now two sets of daughter DNA

evidence for semi conservative replication

Watson and crick discovered the structure of DNA in 1953 (double helix) helped by Rosalind franklins research on X-ray diffraction

Meselson and Stahl conducted an experiment which proved DNA replication must be semi conservative.

type of bond between complementary base pairs

hydrogen

type of bond between adjacent nucleotides in DNA strand

phosphodiester bonds

describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule

condensation reaction between phosphate and deoxyribose catalysed by DNA polymerase

how does separation of strands occur in semi conservative replication

DNA helicase breaks hydrogen bonds between base pairs (AT/GC) (complementary bases)

describe the role of DNA polymerase in the semi conservative replication of DNA

DNA polymerase joins adjacent nucleotides and catalyses condensation reactions which catalyses the formation of phosphodeister bonds between the adjacent nucleotides

role of single stranded DNA fragments in semi conservative replication

1.) they are the template which determines order of nucleotides/bases

role of DNA nucleotides in semiconservative replication

forms complementary pairs (AT) (CG)/ forms complementary DNA strand

give two features of DNA and explain how each one is important in the semi conservative replication of DNA

DNA is double stranded which gets separated by DNA helicase in replication to both be used as a template

weak hydrogen bonds between bases allow two strands to be separated/ unzip

Describe the role of two names enzymes in the process of semi conservative replication

DNA helicase unwinds the DNA strands to form two strands that can act as a template - causes the breaking of hydrogen bonds

DNA polymerase joins the DNA nucleotides

forming phosphodeister bonds

use figure 1 and figure 2 and ur knowledge of enzyme action to explain why the arrows point in opposite directions

Figure 1 shows = DNA has antiparallel strands/ shape of nucleotides is different/ aligned differently

enzymes have active sites with specific shape

only substrates with complementary shape can bind with active site of enzyme/ active site of DNA polymerase

wot.

DNA structure

double helix structure

strands are polynucleotides

made up of lots of nucleotides joined together in a long chain

DNA molecules are long and coiled up very tightly so that a lot of