Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

The structure of a nucleotide as the monomer from which nucleic acids are made
To include the differences between RNA and DNA nucleotides, the identification of the purines and pyrimidines
and the type of pentose sugar
A nucleotide is a monomer of nucleic acids
...

There are two types of nucleic acids (polynucleotides): DNA and RNA
...


There are five possible nitrogenous bases: adenine, thymine, uracil, guanine and cytosine
...
Pyrimidines are smaller than purines due to the presence of a
double carbon ring in purine whereas pyrimidines have a single carbon ring structure
...
The phosphate group at the fifth
carbon of the pentose sugar of one nucleotide forms a covalent phosphodiester bond with the hydroxyl group at the third
carbon of the pentose sugar of an adjacent nucleotide
...

The phosphodiester bonds are broken by hydrolysis reactions
...

ADP (adenosine diphosphate) is formed in the hydrolysis of ATP which releases energy
...

ATP (adenosine triphosphate) is used for energy transfer in all cells of all living things (universal energy currency)
...

ATP is a good immediate energy store because it is rapidly reformed by the
phosphorylation (reattaching a phosphate group to ADP) of ADP
...
However it isn’t a good long term energy store
because of the instability of the phosphate bonds in ATP
...

The reactions are said to be ‘coupled’ as they happen simultaneously
...
It consists of a Deoxyribose sugar, a phosphate group and
a nitrogenous base
...
Each strand is a chain of nucleotides (a
polynucleotide)
...
These bases
pair in the centre of the molecule by means of hydrogen bonds
...
The change in tertiary structure means it has a different function
...

DNA can be extracted from plant material by first grinding the sample in a mortar and pestle to break down the cell walls
...

Salt is then added to break the hydrogen bonds between the DNA and the water molecules
...
Finally alcohol is added which causes the DNA to precipitate out
of the solution
...
The DNA can be picked up
by ‘spooling’ it onto a glass rod
...

Adenine and thymine always join to form two hydrogen bonds
and cytosine and guanine always join to form three hydrogen
bonds
...

Complementary base-pairing is important in DNA replication
because the same sequence of nucleotides is produced which
reduces the occurrence of mutations and allows the reformation of hydrogen bonds
...
This arrangement
maintains a constant distance between the DNA ‘backbones’,
resulting in parallel polynucleotide chains
...

The structure of DNA allows for replication because it is double stranded so both strands act as a template
...
The complementary base pairing means purines are only able to
bind to pyrimidines due to the different sizes of purines and pyrimidines and the difference in hydrogen bonds between A
& T (2H bonds) and C & G (3H bonds)
...

The enzyme helicase unwinds and separates the strands and breaks the hydrogen bonds
...


DNA replication takes place during interphase
...
DNA replication is
considered to be semi-conservative because one strand from the original DNA acts as a template for the newly formed
strand
...
The enzyme DNA helicase causes the double helix
structure to unwind to form two separate stands and the hydrogen bonds between the bases to break
...
Each strand acts as the template for the formation of a new molecule
...
The hydrogen bonds reform and DNA polymerase joins adjacent nucleotides to from the sugar-phosphate
backbone
...

DNA replication conserves genetic information, prevents the occurrence of random, spontaneous mutations and makes
sure the DNA is accurate
...

A gene is a sequence of DNA nucleotides that codes for a polypeptide
...
The genetic code is the DNA code
for a sequence of amino acids
...
The sequence of amino acids in a protein determines its structure and function
...
It is a sequence of three nucleic bases, called a codon
...

One codon acts as the start codon which signals the start of a sequence that code for a protein
...

The genetic code is non-overlapping – triplets are adjacent and the sequence is ‘read’ from base 1 not base 2 or 3
...

The genetic code is universal – all organisms use the four bases and the codon for the amino acid is the same for all
organisms but the sequence of bases coding for each individual proteins is different
...

Transcription and translation of genes resulting in the synthesis of polypeptides
...

DNA is not able to leave the nucleus because it is too big to fit through pores in the nuclear envelope
...

RNA is shorter than a DNA molecule because it only copies one gene or section of DNA whereas DNA comprises of
many genes
...

Transcription is the process of copying sections of DNA base sequence to produce smaller molecules of mRNA
...

Only one of the two strands of DNA contains the code for the proteins to be synthesised
...
The other strand is a complementary copy of the sense strand and doesn’t code for a protein
...

Free RNA nucleotides will base pair with complementary bases exposed on the antisense strand when the DNA unzips
...

Phosphodiester bonds are formed between the RNA nucleotides by the enzyme RNA polymerase
...

MRNA detaches from the DNA template and carries the complementary DNA or genetic code out of the nucleus and
transfers it to the ribosomes, the site of translation, for protein synthesis
...

Translation is the process by which the complementary code carried by the mRNA is decoded by tRNA into a sequence of
amino acids
...
A tRNA with the
complementary anticodon binds to the MRNA start codon
...

Another tRNA with the anticodon and corresponding amino acid binds to the next codon on the mRNA
...
The first amino acid formed is transferred to the second amino acid formed on the
second tRNA by the formation of a peptide bond
...
The ribosome then moves along the mRNA, releasing the first tRNA
...

The process keeps repeating until a stop codon is reached and the polypeptide is released
...
This folding and the bonds that are formed are determined by the sequence of amino acids in the
primary structure
...

RNA molecules exist in three forms:
 mRNA is the coding strand made complementary to the template strand
...

 rRNA is found in the ribosomes
...




---