DNA Replication (MCB school revision)

Okazaki fragment - short fragment of DNA.

Helicase - separates the double strand.

Single-strand binding protein – prevents single strand coiling back to original shape.

DNA Polymerase synthesize only 5’ to 3’.

5’ to 3’ (direction of DNA polymerase) = Leading strand (3’ to 5’ old strand, 5’ to 3’ new strand, direction towards helicase)

5’ to 3’ (direction of DNA polymerase) = Lagging strand (5’ to 3’ old strand, 3’ to 5’ new strand, direction away from helicase)

Leading strand –

1) RNA Primase - attach a RNA Primer onto the strand
2) DNA Polymerase 3 - adds deoxyribonucleotides to synthesize the new complementary strands of DNA.

Lagging Strand –

1) RNA Primase – attaches a RNA Primer
2) DNA Polymerase III - adds deoxyribonucleotides
3) DNA Polymerase I – removes the RNA and replace it with DNA
4) DNA ligase – Forms phosphodiester bonds

Molecular and Cell Biology (School revision) - Transcription and translation

In order to undergo the central dogma, the DNA has to undergo transcription and translation.

In transcription, the RNA Polymerase splits the double strand into a single strand. The RNA Polymerase will then bring the nucleotides, and then the nucleotides will firstly find the start codon. After finding the start codon, the RNA Polymerase will then begin to bind the nucleotides to form a single strand. As the RNA Polymerase moves along to form a longer RNA strand, the front part of the mRNA will detached from the single strand, and after the RNA Polymerase reaches the stop codon, the mRNA strand will be formed.

The mRNA strand will then move out of the nucleus to the cytoplasm, and then translation will occur.

For translation, firstly, the ribosome will bind onto the mRNA strand, and then it will also find the start codon. After it found the start codon AUG, it will then start to read.

As it moves along, the tRNA with the anti-codon on the other side will then bind onto the codon. On the other end, it has the amino acid. As the ribosome moves along, there will be more tRNA binding onto the codon.

As the ribosome moves along, the tRNA on the front part will started to detached with the mRNA strand, and leaving behind the amino acid. The ribosome will also help to form the peptite bond of the amino acid.

After the ribosome reaches the end codon, the amino acid will then be formed.

In order to form protein, there will be more amino acids formed, which will then made up proteins.

Immunology - Complement System C1 to C9

In Complement System, there are different types of proteins in the complement system. These proteins are named from C1 to C9.

Firstly, the antibody will bind onto the infectious particle. After that, C1 will attached onto the antibody.

After attaching onto the antibody, C1 will then be activated, and then it will split to form C2a and C4b fragments.

When these 2 fragments joined together, it will then form the C3 convertase.

C3 convertase is able to cleave C3 into C3a and C3b.

C3a is able to cleave C5 into C5a and C5b.

C5b, C6, C7, C8, and C9 are able to attach itself onto the infectious cell membrane, and therefore opening a hole on the membrane, and allowing the infectious cell content to lysate, and it leads to self-destruct. This process is known as MAC, which is known as Membrane Attacking Complex.

C3b is able to attach itself to the infectious cell, and therefore it will help in opsonisation, and it will then undergo phagocytosis.

Clonal Selection (School Revision) Immunology

Clonal Selection is the process of forming new antibodies. When there is a new antigen(foreign infectious particles) invading our body, it will trigger the immune system. The T-cell will then activate the B-cell. After the B-cells are being activated, it will start to undergo a few cell divisions. After going through many cell divisions, it will form many memory cells and plasma cells.

The functions of the memory cell is to store the information of the specific antibody that has the immunity against the new antigens. If there are memory cells, the immune system will then be able to produce the specific antibody that has immunity to the new antigens.

The functions of the plasma cells is to produce antibodies to fight against the new foreign antigens.

After we recovered from the disease, the memory cell still remains in our body. Therefore if we infected the same disease again, we still have the memory cell which are present in our body, therefore, the plasma cell will produce the same antibody to fight against the disease. Therefore we can have immunity on the second time we infected the same disease.