Nucleotides and nucleic acids

structure of a nucleotide

. contains a pentose sugar (sugar with 5 carbons)

. a nitrogenous base

. a phosphate group

what do nucleotides contain

. all nucleotides contain carbon, oxygen, hydrogen, nitrogen and phosphorous

. they are monomers make up RNA and DNA (DNA is used to store the genetic information and RNA is used to make proteins by carrying out instructions encoded by the DNA)

. ADP and ATP are types of nucleotides that are used to store and transport energy in cells

what are purines and pyrimidines

. Adenine and Guanine are purines

. Uracil/ Thymine and Cytosine are pyrimidines

. a purine base contains 2 nitrogen rings joined together

. a pyrimidine contains only one nitrogen ring so is smaller than purines

structure of DNA

. its backbone lacks an oxygen atom at the 2’ carbon position making it highly stable

. it contains Adenine, Guanine, Cytosine and Thymine

. it has two stands coiled to together that forms a highly stable double helix shape

. its very long an is made of millions of base pairs

structure of RNA

. its backbone contains a hydroxyl group at the 2’ carbon position making it very unstable and reactive

. it contains Adenine, Guanine, Cytosine and Uracil

. it has a single strand which allows it to fold into complex 3D shapes

. its short and is typically a few hundred to thousand nucleotides long

structure of ATP and ADP

. ADP (adenosine diphosphate) contains an adenine base, ribose sugar and 2 phosphate groups

. ATP (adenosine triphosphate) contains an adenine base, ribose sugar and 3 phosphate groups

formation and breakdown of ATP

. ATP is synthesised from ADP na dan inorganic phosphate using energy from an energy-releasing reaction

. then ADP is phosphorylated to form ATP and a phosphate bond is formed

. energy is stored in the phosphate bond, when this energy is needed by a cell ATP is broken down to ADP and Pi, this energy is then released by the phosphate bond and used up by the cell

formation and breakdown of phosphate bonds

1) the nucleotides join up between a phosphate group of one nucleotide and the sugar from another via a condensation reaction, this forms and ester bond

2) the chain of sugars and phosphates is known as the sugar-phosphate backbone

3) polynucleotides can be broken down into nucleotides again by breaking down the phosphodiester bonds by hydrolysis

formation of DNA

1) 2 DNA nucleotide stands join together by hydrogen bonding between the bases

2) each base can only pair with their complementary base pairs (A-T and C-G, a purine always pairs with a pyrimidine)
3) two hydrogen bonds form between A and T but three hydrogen bonds form between C and G

4) two antiparallel polynucleotide strands are twisted to form the DNA double helix

DNA purification investigation

1) break up the sample using a pestle and mortar

2) make a solution of dilute washing up liquid , salt and distilled water

3) add the broken up cells into a beaker containing the detergent solution, then incubate the. beaker in a water bath at 60 degrees for 15mins

4) once incubated put the beaker in an ice bath too cool the mixture, once its cooled filter the mixture and transfer a sample to a clean test tube

5) add protease enzyme to the filtered mixture then slowly dribble some cold ethanol down the side of the test tube, so it forms a layer on top of the DNA-detergent mixture

6) leave the mixture for a few minuets until it forms white precipitate at the top which can then be extracted with a glass rod

what does the washing up liquid, salt and hot water bath do to the broken sample

. the detergent breaks down the cell membrane to extract the DNA

. the salt dins to the DNA and causes it to clump together

. the temperature of the water bath should stop enzymes from working and breaks down the DNA from the sample

what does protease do to the DNA

it breaks down the proteins that are bound to the DNA

process of DNA replication

1) DNA helicase breaks the hydrogen bond between the two polynucleotides DNA strands and the helix unzips and forms 2 single stands

2) each original strand acts as a template for a new strand, and free-floating nucleotides join to the exposed bases on the original strand by complementary base pairing

3) the nucleotides of the new strand are joined together by DNA polymerase which forms the sugar-phosphate backbone and H bonds form between the bases on the original and new strand

4) these strands contain a new DNA molecule from the original and new strand

why is it called semi-conservative replication

. because only half of the strand is new

. DNA replication is very accurate and has to be to ensure genetic information is conserved every time DNA is replicated

. every so often a random spontaneous mutation occurs which changes the amino acids in the protein which changes the DNA sequence, this can cause abnormal proteins to be produced (these can be harmful or beneficial) mutations

what is the non-overlapping code

in the genetic code each base triplet is read in the sequence separate from the triplet before and after it so they are not overlapping

what is the degenerate code

there are more possible combinations of triplet than there amino acids (there are 20 amino acids and 64 possible triplets), this means some amino acids are coded for more than one base triplet

what is the universal code

the same specific base triplets code for the same amino acids in all living things

properties of messenger RNA (mRNA)

. made in nucleus

. it has three adjacent bases called a codon

. it carries the genetic code from the DNA in the nucleus to the cytoplasm, where it is used to make protein during translation

properties of transfer RNA (tRNA)

. found in the cytoplasm

. it has an amino acid binding site at one end of 3 bases at the other end called an anticodon

. it carries the amino acids that are used to make proteins to the ribosomes during translation

properties of ribosomal RNA (rRNA)

. forms the two subunits in ribosomes along with proteins

. the ribosome moves along the mRNA strand during protein synthesis, and rRNA helps to catalyse the formation of peptide bonds between amino acids

process of transcription

1) DNA helicase breaks the hydrogen bonds between bases, causing the DNA to unzip

2) one of the DNA strands is then used as a template to make an mRNA copy, and RNA polymerase moves along the DNA template strand and attaches free nucleotides to their complementary base pairs

3) once the nucleotides have paired up with their specific bases they form an mRNA molecule

4) RNA polymerase continues making a strand of mRNA until it reaches a stop codon

5) mRNA now moves out of the nucleus via the nuclear pore and attaches to a ribosome for translation

process of translation

1) the mRNA attaches to the ribosome and tRNA, then a tRNA molecule with an anticodon complementary to the start codon on mRNA attaches itself to its complementary base

2) a second tRNA molecule attaches itself to the next codon on mRNA in the same way

3) rRNA catalyses the formation of peptide bonds between the two amino acids attached to tRNA molecules and joins to the amino acid

4) a third tRNA molecule binds to the next codon on mRNA and its amino acid binds to the first two and the second tRNA molecule moves away

5) this process continues producing a chain of linked amino acids, a polypeptide chain until there is a stop codon on the mRNA

6) the polypeptide moves away from the ribosome and translation is complete