Week 8: DNA replication/repair, mitosis and the cell cycle

Semi-conservative replication

both strands are used as the template for two new strands so each of the copied DNA sequences contain and original strand and a copy

DNA Polymerase

building a complementary strand in the 5’ to 3’ direction (therefore copying the strands that run in the 3’ to 5’)

Primase

makes a short sequence of RNA that acts as a primer for this

Helicase

sit at the replication fork to separate the strands

Single stranded binding proteins

Keep the strands seperate

Topoisomerase

relieves the tension caused by separating the strands by breaking, swivelling and rejoining one of the strands

Okazaki fragments

The lagging strand needs to be copied in pieces. Needs an RNA primer

Joining of Okazaki fragments

DNA ligase which finishes the last connection in a sugar phosphate backbone

Proliferation

The process in which a cell divides in two

G1

the cell has received a signal to divide and starts the process by increasing the cell contents including the organelles, nutrients, building blocks of membranes and proteins BUT NOT the genomic DNA

G1 checkpoint

make sure that it has everything that it needs to become two functional cells at the end

S phase

the DNA synthesis phase, all of the DNA is copied

G2

DNA is checked and the cell confirms the external and internal environments are good for division

Interphase

G1, S and G2

M Phase (mitosis)

prophase, metaphase, anaphase, telophase and cytokinesis

Prophase

the two copied centrosomes each with their two centrioles start migrating to the opposite poles of the cell (division will be between) , the nuclear membrane begins to break down, the chromosomes start to condense

Metaphase

the centrosomes organise microtubules into the spindle and the condensed chromosomes line up on the ends held at the centromere onto the spindle via the proteins of the kinetochore

Anaphase

the kinetochores on opposite spindles start to slide towards the centrosome and pull the chromosome pairs apart

Telophase

the chromosomes are now at separate sides of the cell and they start to unwind.  Two new nuclear membranes start to form around them and the cell starts to constrict in the middle to get ready for cytokinesis

Cytokinesis

the cell divides into two new cells

M checkpoint

ensures that the homologous chromosomes are lined up correctly in their pairs on the spindle so they can be separated properly in to the new cells