BY1 - Nucleic acids and their functions

Polymers, made of monomers called nucleotides. 

A phosphate group, a pentose sugar and an organic/nitrogenous base which are combined by a condensation reaction.

Pyrimidine - thymine, cytosine and uracil

Purine - adenine and guanine

Adenosine triphosphate.

It contains the base adenine, the sugar ribose and three phosphate groups.

Enzyme ATPase hydrolyses bond between 2nd and 3rd phosphate groups in ATP, removing the third phosphate, leaving only two.

ATP molecule is hydrolysed into adenosine diphosphate (ADP) and an inorganic phosphate ion, releasing energy.

ATP + water ⇌ ADP + Pi

ADP and an inorganic phosphate ion combine in a condensation reaction, to make ATP and water - phosphorylation.

Hydrolysis of ATP to ADP involves a single reaction, energy released immediately, whereas breakdown of glucose involves many reactions and takes longer to release energy.

One enzyme needed to release energy from ATP, many needed in glucose.

ATP releases energy in small amounts, when and where needed, but glucose contains large amounts which could be released all at once.

ATP provides a common source of energy for different reactions, increasing efficiency and control by the cell.

Metabolic processes - building lage complex molecules from smaller, simpler molecules

Active transport - changing the shape of carrier proteins, allowing molecules/ions to be moved against a concentration gradient

Movement - for muscle conctration

Nerve transmision

Secretion - packaging and transport of secretory products into vesicles in cells

Two polynucleotide strands wound around eachother to form a double helix

Pentose sugar deoxyribose

Bases adenine, thymine, cytosine and guanine

Deoxyribose and phosphate are on outside of DNA molecule acting as a backbone

Bases of the two strands face inwards, and hydrogen bonds join bases into complementary pairs (a-t, c-g). Hydrogen bonds maintain shape of double helix.

Very long and thin, tightly coiled in a chromosome. Double helix is 2nm in diameter

Strands are antiparallel

Its very stable as information content passes from generation to generation without changing

A very large molecule, carries a large amount of genetic information

Two strands are able to separate as they're held by hydrogen bonds

Genetic information is protected as bases on the inside, within the backbone

Single-stranded polynucleotide

Contains the pentose sugar ribose

Bases adenine, guanine, cytosine and uracil

A long single-stranded molecule

Synthesised in the nucleus and carries genetic code from the DNA to the ribosomes in the cytoplasm

Found in the cytoplasm, comprises large, complex molecules

Ribosomes are made of ribosomal RNA and protein, they're the site of translation of the genetic code into protein.

A small, single-stranded molecule, folds so that in places there's base sequences forming complementary pairs

The 3' end has the base sequence c-c-a, where the specific amino acid the molecule carries is attached

It carries a sequence of three bases, the anticodon

tRNA transports specific amino acids to the ribosomes in protein synthesis

Watson and Crick in 1953. They used the information obtained by many scientists such as Franklin and Wilkins.

DNA replication and protein synthesis

Conservative replication - parental double helix remains intact and a whole new double helix is made.

Semi-conservative replication - the parental double helix separates into two strands, each of which acts as a template for the synthesis of a new strand.

Dispersive replication - two new double helices contain fragments from both strands of the parental double helix.

Semi-conservative replication

It is a triplet code, three bases code for one amino acid

There are 64 possible codes, but only 20 amino acids found in proteins. More than one triplet can encode each amino acid, the code is degenerate/redundant

The code is punctuated, three triplet codes don't code for amino acids, they're called stop codons in mRNA and mark the end of a portion to be translated

Code is universal, in all organisms known the same triplet codes for the same amino acid

Code is non-overlapping, each base occurs in only one triplet

Introns are non-coding sequeneces in DNA and pre-mRNA, they are cut out of the pre-mRNA using endonucleases. The sequences that are left over are exons, they are joined together or spliced with ligases.

Transcription and translation

Enzyme DNA helicase breaks H bonds between bases, causes two strands to separate and unwind

Enzyme RNA polymerase binds to template strand 

Free RNA nucleotides align opposite template strand based on complementary base pairs 

RNA polymerase moves along DNA, forming bonds that add RNA nucleotides, resulting in the synthesis of mRNA alongside unwound portion of DNA. Behind RNA polymerase, DNA strands rewind to reform double helix.

RNA polymerase separates from template strand once a 'stop' codon is reached

Production of the transcript is complete, newly formed RNA detaches from DNA

Initiation: ribosome attaches to a 'start' codon at one end of mRNA. 1st tRNA with an anticodon complementary 1st codon on mRNA attaches to the ribosome and bond with H bonds. 2nd tRNA with an anticodon complementary to 2nd codon on mRNA attaches to other attachment site and bond.

Elongation: two enzymes are close and form a peptide bond. 1st tRNA leaves the ribosome and returns to cytoplasm. Ribosome moves one codon along the mRNA strand and next tRNA binds.

Termination: sequence repeats until a 'stop codon' is reached. The ribosome-mRNA-polypeptide complex separates.

The tRNA molecule is released from the cytoplasm and it's free to collect another amino acid from the amino acid pool in the cytoplasm. Energy from ATP is needed to attach the amino acid to the tRNA.

The modification of a polypeptide. It can be chemically modified by combination with non-proteins such as: carbohydrate, making glycoproteins and lipid, making lipoproteins, and phosphate, making phospho-proteins.