nucleotides

describe the structure of a nucleotide

made from a pentose sugar, a nitrogenous base and a phosphate group.

what elements do all nucleotides contain?

H, O, N, P

what is the structure of a DNA nucleotide?

it has got a phosphate group, deoxyribose sugar and a nitrogenous base. the base on each nucleotide can vary between four bases - Adenine (A), Thymine (T), cytosine (C) and Guanine (G).

what is the structure of an RNA nucleotide?

It has got a phosphate group, a ribose sugar and a nitrogenous base. in RNA Uracil (U) replaces Thymine (T) as a base.

what are the two types of base present in DNA and RNA molecules?

purines and pyrimidines.

which two bases are purines?

adenine and guanine

which three bases are pyrimidines?

cytosine, thymine and uracil.

what is the difference in structure of a purine and pyrimidine base?

a purine base contains two carbon-nitrogen rings joined together, whereas a pyrimidine base only has one carbon-nitrogen ring. so a pyrimidine base is smaller than a purine base.

what types of nucleotides are ADP and ATP?

they are phosphorylated nucleotides.

how do you phosphorylate a nucleotide?

you add one or more phosphate group to it.

describe the structure of ADP?

consists of the base Adenine, the sugar ribose and two phosphate groups.

describe the structure of ATP?

consists of the bases adenine, a ribose sugar and three phosphate groups.

how is ATP made?

ATP is synthesised from ADP and inorganic phosphate (P). The ADP is phosphorylated to form ATP and a phosphate bond is formed.

how is ATP broken down to release energy?

• hydrolysis reaction

• energy is stored in the phosphate bond, so when energy is needed, ATP is broken back down into ADP and inorganic phosphate.

• energy is released from the phosphate bond and used by the cell.

what is the difference between prokaryotic and eukaryotic DNA?

• in eukaryotes, DNA is found mainly inside the nucleus.

• in prokaryotes, DNA is not enclosed in a membrane.

describe the role of mRNA?

• transfers genetic information from the nucleus to the ribosomes in order to make proteins.

what forms a phosphodiester bond?

a condensation reaction between a sugar group on one nucleotide and a phosphate group on a different nucleotide.

what are three important features of the genetic code?

• universal - the same four bases are used in the DNA of every organism (A,C,T,G) and the same codon codes for the same amino acids in every organism.

• non-overlapping - means that there is no overlap between triplet codes, each triplet code is separated from other triplet codes in the chromosome.

• degenerate - some amino acids are encoded by more than one codon.

what is the structure of DNA?

• double helix/ two polynucleotide chains

• the sugar and phosphate lie on the outside of the helix and forms DNA’s backbone.

• the nitrogenous bases are stacked on the inside of the helix.

• hydrogen bonds hold the bases together.

what is the structure of RNA?

• relatively short polynucleotide chain

• made of ribonucleotides that are linked by phosphodiester bonds

what are the types of bonding in DNA and RNA?

• complimentary base pairing holds the two DNA polynucleotide chains together by hydrogen bonds.

• the single polynucleotide chain is held together by phosphodiester bonds between nucleotides.

describe the process of DNA replication?

• DNA helicase binds to DNA and breaks the hydrogen bonds between the two strands.

• the DNA helix unwinds and the two strands separate.

• free-floating nucleotides form hydrogen bonds with the exposed complimentary bases. (each strand is used as a template to produce complimentary strands).

• DNA polymerase forms phosphodiester bonds between the nucleotides.

• the two new DNA strands are synthesised.

what is the chemical equation for the hydrolysis of ATP?

ATP + H2O = ADP + Pi (+ energy)

what is the chemical equation for the re-synthesis of ATP?

ADP + Pi (+ energy) = ATP + H2O

what are the two steps that occur in protein synthesis?

• transcription

• translation

describe the process of translation

• RNA polymerase binds to the DNA at the beginning of a gene.

• the hydrogen bonds between the two DNA strands break, separating the strands, and the DNA molecule uncoils at that point and the bases of the target gene are exposed.

• RNA polymerase binds free-floating RNA nucleotides to the template strand.

• the RNA nucleotides form a mRNA strand that is complimentary to the template strand.

• RNA polymerase eventually reaches the triplet of bases that signal ‘stop’, this causes the RNA polymerase to stop unzipping DNA and producing mRNA.

• the mRNA strand is separated from the template strand by RNA polymerase.

• the hydrogen bonds between the two strands form again and the strands join together.

• the completed mRNA strand leaves the nucleus and enters the cytoplasm, and the mRNA is used in translation.

describe the process of translation

• mRNA that has been produced during transcription, bind to a ribosome in the cytoplasm.

• tRNA molecules carry amino acids to the ribosome.

• one molecule of tRNA binds to the first codon in the ribosome.

• the tRNA molecule has an anticodon that is complimentary to a specific codon.

• a tRNA molecule binds to the second codon in the ribosome.

• the two amino acids in the ribosomes form a peptide bond.

• as this process continues, a polypeptide chain of amino acids is created.

• when the ribosome reaches a ‘stop’ codon, there is no corresponding tRNA molecule.

• the polypeptide chain is released from the ribosome.

what are some differences between the structure of tRNA and mRNA?

• mRNA has more nucleotides than tRNA.

• mRNA is a straight molecule, but tRNA is folded.

• mRNA has no paired bases/hydrogen bonds but tRNA does have some paired bases.