Summary - AQA Alevel biology protein synthesis (9700)

Protein Synthesis
Alevel note series by Emaan Atif
Introduction to Genetic Materials:

 Characteristics:
 Ability to carry instructions/information, blueprint for the construction and behavior of cell.
 Ability to be copied: Pass on exact copy of information to daughter cells

Nucleic acids:

 Monomer = Nucleotides
 Bond between adjacent monomers after condensation = phosphodiester bond
 Bond between complementary base pairs = hydrogen bond
 Polymer = Polynucleotides
 2 types: DNA and RNA
 A nucleotide consists of:
1. Nitrogenous base : Purine or pyrimidine base
2. Pentose sugar : 5 carbon sugar, either deoxyribose or ribose
3. Phosphate group: Negatively charged, making DNA a negatively charged molecule &
 2 major types of nitrogenous bases:
 Purine bases — has 2 rings: (Pure As Gold)
1. Adenine
2. Guanine
 Pyrimidine bases — has 1 ring only: (CUT)
1. Cytosine
2. Uracil (RNA only)
3. Thymine (DNA only)
 Pairing of bases is precise
 Purine always binds with pyrimidine
 So DNA molecule has same width throughout
 RNA nucleotide molecule has OH and
DNA has H only.

RNA has one extra oxygen.

,ATP

 Adenosine triphosphate (ATP) is the energy-carrying molecule that provides the energy to drive
many processes inside living cells
 ATP is another type of nucleic acid and hence it is structurally very similar to the nucleotides that
make up DNA and RNA
 It is a phosphorylated nucleotide
 Adenosine (a nucleoside) can be combined with one, two or three phosphate groups
o One phosphate group = adenosine monophosphate (AMP)
o Two phosphate groups = adenosine diphosphate (ADP)
o Three phosphate groups = adenosine triphosphate (ATP)




DNA structure:

 DNA molecules are made up of two polynucleotide strands lying side by side, running in opposite
directions – the strands are said to be antiparallel
 Each DNA polynucleotide strand is made up of alternating deoxyribose sugars and phosphate groups
bonded together to form the sugar-phosphate backbone. These bonds are covalent bonds known
as phosphodiester bonds
o The phosphodiester bonds link the 5-carbon of one deoxyribose sugar molecule to the phosphate
group from the same nucleotide, which is itself linked by another phosphodiester bond to the 3-
carbon of the deoxyribose sugar molecule of the next nucleotide in the strand
o Each DNA polynucleotide strand is said to have a 3’ end and a 5’ end (these numbers relate to
which carbon on the pentose sugar could be bonded with another nucleotide)
o As the strands run in opposite directions (they are antiparallel), one is known as the 5’ to 3’
strand and the other is known as the 3’ to 5’ strand

Hydrogen bonding

 The two antiparallel DNA polynucleotide strands that make up the DNA molecule are held together by
hydrogen bonds between the nitrogenous bases
 These hydrogen bonds always occur between the same pairs of bases:
o The purine adenine (A) always pairs with the pyrimidine thymine (T) – two hydrogen bonds are
formed between these bases
o The purine guanine (G) always pairs with the pyrimidine cytosine (C) – three hydrogen bonds are
formed between these bases
o This is known as complementary base pairing
o These pairs are known as DNA base pairs

, DNA is a double helix structure.




Semi-conservative Replication:
 Occurs in the nucleus during S phase of interphase
 Requires ATP
 Enzymes needed:
 Helicase: To break H bonds to separate 2 DNA strands
 DNA polymerase:
1. To synthesize a new strand of DNA (in the 5’ to 3’ direction)
2. To catalyze the formation of phosphodiester bond
3. Proofreads DNA
 DNA ligase:
1. To join, DNA fragments together
2. To catalyze the formation of phosphodiester bonds