Nucleic Acids

1) Carries the genetic code for protein synthesis in all cells

2) Replicates itself, ensuring the DNA is accurately copied for cell division

~ Many repeating monomers called nucleotides which bond together

~ Forming polynucleotides

~ Pentose (5 carbon) sugar

~ Phosphate

~ Nitrogenous base

~ Deoxyribose

~ Made up from 2 strands of polynucleotides, wound into a double helix

~ The 2 strands of the double helix are held together by weak hydrogen bonds between pairs of nitrogenous bases

~ Adenine and thymine (2 hydrogen bonds)

~ Cytosine and guanine (3 hydrogen bonds)

~ It ensures that the DNA replicates correctly

~ As there will be the same proportion of adenine and thymine to cytosine and guanine in a DNA molecule

~ Messenger RNA (mRNA)

~ Transfer RNA (tRNA)

~ Ribosomal RNA (rRNA)

~ Transports amino acids to the ribosome for the translation stage of protein synthesis

~ tRNA has an anticodon and an amino acid site

1) RNA and DNA is composed of nucleotides, forming polynucleotide strands

2) Each nucleotide is made up from phosphate, pentose sugar and base

3) There are 4 bases in RNA and DNA

1) RNA molecule have only 1 polynucleotide strand, DNA molecule comprise of 2 strands

2) DNA= Deoxyribose RNA= Ribose

3) DNA= Thymine RNA= Uracil (pairing with A)

4) DNA - remains within a cell for the whole of a cell cycle

RNA- is synthesised and then broken down after use

~ The nucleotide ATP (adenosine triphosphate)

~ Ribose (pentose sugar)

~ Adenine nitrogenous base

~ 3 phosphate groups

~ ADP + Pi

~ And energy is required to form a high energy bond between the 2nd and 3rd phosphate groups

~ ATP releases large amounts of energy

~ ADP (adenosine diphosphate) + Pi (inorganic phosphate) is formed

~ During respiration from breakdown of glucose

~ Where chemical energy is transferred to cellular processes which require energy

~ It supplies energy

~ Used in all reactions, in all cells

~ In all organisms

~ Only one enzyme is needed to release energy from ATP (glucose needs many)

~ ATP releases energy in small amounts when needed (glucose releases large amounts - which might not be needed)

~ Soluble

~ Can be transported across (organelle) membranes easily

~ So that when the cells divide each daughter cell receives exact copy of the genetic information

1) Original DNA strands unwind and then unzips due to hydrogen bonds being broken

~ Catalysed by helicase enzyme

2) Each polynucleotide strand acts as a template for free DNA nucleotides align opposite unpaired exposed DNA bases

3) Free DNA nucleotides complimentary base pair and join to exposed bases

~ They bind to one another forming hydrogen bonds

~ DNA polymerase joins the DNA nucleotides together to form a complementary DNA polynucleotide strand

4) 2 double stranded DNA are formed

~ DNA acts as a genetic code for synthesising proteins

~ Enzymes are proteins

~ Enzymes catalyse all cell's reactions + the cell's characterises and functions

~ 3 letter (base) or triplet code

~ Each sequence codes for one specific amino acid

~ The DNA triplet code of its gene is converted in to a molecule of mRNA, by complementary base pairing.

~ A triplet code in mRNA is called a codon

~ Exon or gene

~ This is the basis of the 'one gene one polypeptide' hypothesis

~ Regions of non-coding DNA called introns

~ Regions of non-coding DNA

~ Made up of a polypeptide chain

~ Which are amino acids joined together with peptide bonds

~ The unique sequence of amino acids

~ Exon or gene

All triplet codes/ codons are universal

~ Transcription

~ Translation

~ Occurs in the nucleus

~ The translation of the code into primary strcuture protein

~ Occurs at ribosomes in the cytoplasm

~ The mechanism by which the base sequence of a gene on a DNA strand in converted into a complementary base sequence of mRNA

1) DNA is physically too big to leave the nucleus via nuclear pores

2) RNA polymerase binds to DNA at the gene/ exon (specific sequence of DNA bases) to be copied and unwinded

3) DNA unzips

4) Only one of the DNA strands is used as a template

5) Free RNA nucleotides align themselves opposite the complementary DNA base and joins = G to exposed C & A-U

6) RNA polymerase moves along the strand joining nucleotides forming single stranded DNA

7) mRNA now carries the complementary codons - which code for specific amino acids

8) At the end the sequence of mRNA detaches and DNA rewinds

9) mRNA transfers nucleotides through the nuclear pores to the cytoplasm

- where it attaches to ribosomes consisting of ribosomal RNA and protein

~ In the nucleus

~ RNA polymerase

~ Binds to the gene/ exon of DNA

~ To be copied and unwinds

~ Then moves along the strand, joining nucleotides forming single stranded mRNA

~ messenger RNA (mRNA)

~ It is a single strand

~ Forms a 'clover leaf' shape due to base pairing being possible in certain sections of the molecule

~ Anticodon

1) It determines the specific amino acids that attaches to that tRNA molecule

~ Therefore the sequence of amino acids in the polypeptide chain

2) Only the anti-codon can base pair with the codon on the mRNA which is complementary

2) A ribosome attaches to the mRNA strand which is held in place

3) In the surrounding cytoplasm an amino acid is activated by ATP and is attached

- to a specific tRNA molecule via specific attachment site

- which carries amino acid at one end and an anticodon at the other

4) tRNA molecules bring specific amino acids to the mRNA

5) The anti-codon of the tRNA complementary base pairs to the start codon of the mRNA

6) tRNA forms hydrogen bonds with mRNA

7) Another tRNA complementary base pairs to the second codon of the mRNA

8) A ribosomal enzyme catalyses peptide bond (requiring ATP) formation between an amino acid on one tRNA and the growing polypeptide on the other tRNA

9) The first tRNA is released and returns to the cytoplasmic pool to join to the same specific amino acid

10) A ribosome passes along mRNA, one codon at a time

- tRNA with the appropriate anticodon fills the vacant slot and the amino acid forms a peptide bond with the last member of the chain using energy from ATP

-until a stop codon is reached

~ In the golgi body e.g. glycoprotein

~ A protein may consist of more than one polypeptide e.g. fibrous and quaternary proteins

~ tRNA molecules bring specific amino acids to the mRNA

~ 1

~ It returns to the cytosplamic pool

~ To join to the same specific amino acid

~ The amino acid forms a peptide bond with the last member of the chain

~ Using ATP

~ A ribosomal enzyme

~ Which catalyses the formation of a peptide bond forming between an amino acid on one tRNA and the growing polypeptide on the other tRNA

~ Requiring ATP