3.8 (2.1.2) Nucleic acids

define nucleic acids

large polymers formed from many nucleotides linked together in a chain that contain C, H, O, N, and P atoms

PO^₄2-

phosphate group which is an inorganic molecule that is acidic

how are nucleotides linked together to form polynucleotides

condensation reactions

describe phosphodiester bond

the phosphate group at the fifth carbon of the pentose sugar (5’) forms a covalent bond with the hydroxyl group at the third carbon (3’) of the pentose sugar of an adjacent nucleotide which forms a long, strong sugar-phosphate backbone with a base attached to each sugar

define deoxyribose

a sugar with one fewer oxygen atoms than ribose

define pyramidine

smaller bases which contain single carbon ring structures

define purine

larger bases which contain double carbon ring structures

examples of pyramidines

thymine, cytosine and uracil

examples of purines

adenine and guanine

how many bonds do the complementary base pairings of adenine and thymine form

2

how many bonds do the complementary base pairings of cytosine and guanine form

3

how are the strands of the double helix of DNA held together

hydrogen bonds

why are the two parallel strands of DNA described to be antiparallel

the strands run in opposite directions

difference between RNA and DNA

the pentose sugar in RNA is ribose whereas the pentose sugar in DNA is deoxyribose

what happens to RNA after protein synthesis

RNA disintegrates in the cytoplasm. the phosphodiester bonds are hydrolysed and RNA nucleotides are released and reused

differences between RNA and DNA

RNA has the sugar ribose/ DNA has deoxyribose, RNA has uracil/ DNA has thymine, RNA is single stranded/ DNA is double stranded, RNA does not form a double helix, DNA forms a double helix

steps of DNA replications

1) DNA helicase attaches to the DNA molecule and moves along its length

2) hydrogen bonds holding the DNA strands together are broken and the two strands of helix begin to separate

3) free nucleotides are bonded together by DNA polymerase

4) two identical DNA molecules are formed which are semi-conservative

define semi conservative

each new molecule of DNA produced consists of one old strand of DNA and one new strand

steps of transcription

1) free RNA nucleotides positioned to complementary bases on the template strand 2) RNA polymerase binds to the gene to form phosphodiester bonds 4) mRNA is formed as a copy of the coding stand of DNA

steps of translation

1) mRNA leaves through nuclear pores and goes to the ribosome

2) ribosomes bind to mRNA

3) tRNA brings amino acids to the ribosomes

4) 3 bases stick down of the tRNA called the anticodon

5) the codon on the mRNA is complementary to the anticodon on the tRNA which brings the correct amino acid

6) 2 tRNA can be in the ribosomes at once and peptide bonds form

7) tRNA leaves to pick up a new amino acid of the same type

describe the leading strand

DNA only unzips and unwinds in the direction of 3’ to 5’. the strand that is unzipped from the 3’ end can be continuously replicated as the strand unzips. this strand undergoes continuous replications

describe the lagging strand

DNA only unzips and unwinds in the direction of 3’ to 5’. the lagging stand is unzipped from the 5’ end so DNA polymerase has to wait until a section of the strand has unzipped and then work back along the strand. this results in DNA being produced in sections called Okazaki fragments which then have to be joined. this strand undergoes discontinuous replication

define degenerate code

coding for an amino acid by more than one codon

structure of ATP

a nitrogenous base adenine, a ribose sugar, and three phosphate groups

word equation for hydrolysis reaction of ATP

adenosine triphosphate + water = adenosine diphosphate + inorganic phosphate (+ energy)

why is ATP considered not a good long term energy store

the instability of the phosphate bonds in ATP

define phosphorylation

reattaching a phosphate group to an ADP molecule

properties of ATP

small so it can move easily into, out of and within cells. water soluble. releases energy in small quantities so energy is not wasted as heat. contains bonds between phosphates with intermediate energy meaning its large enough for cellular reactions and energy is not wasted as heat. easily regenerated