4. cell cycle and mitosis Flashcards
why does DNA replication occur
All cells need DNA to be able to make proteins.
When a cell (the parent cell) divides into two daughter cells, each daughter cell must inherit the full set of DNA from the parent cell.
If this wasn’t the case, the daughter cells wouldn’t be able to make all the necessary proteins for their survival.
DNA helicase function
-unzips double helix
-breaks relatively weak H bonds between complementary base pairs
RNA primase function
adds an RNA primer to the 3’ end of the leading strand that allows DNA polymerase to begin to synthesize a new DNA strand complementary and specific to the template strand
DNA polymerase
begins to synthesise a new DNA strand that is complementary and specific to the template strand by joining free nucleotides via complementary base pairing
DNA ligase function
Joins Okazaki fragments by their sugar phosphate backbone on the lagging strand
Chromosome
Thread like structure composed of DNA and associated proteins (histones) containing many genes at specific loci
5 steps in binary fission
- DNA replication
2.Elongation - Septum formation
- Cytokinesis
what happens in elongation
cytoplasmic membrane elongates separating DNA molecules
what happens in septum formation
cross wall begins to form.
membrane invaginates.
what is an RNA primer and what is its function
An RNA Primer is a short sequence of RNA nucleotides (5~10 nucleotides long) that is complementary to the template strand.
It provides an attachment site for DNA polymerase.
what happens during G1
Cell growth, Production of enzymes involved in DNA replication, Normal cellular functions.
what happens in G2
Cell growth/ Normal cellular functions/ Preparation for mitosis (producing proteins involved in mitosis).
what happens in prophase
DNA condense into chromosomes and become visible.
Nuclear membrane disappears.
Centrosomes migrate to two opposite poles of the cell.
what happens in metaphase
Chromosomes align along the equator of the cell.
Spindle fibres attach to the centromeres of the chromosomes.
what happens in anaphase
Sister chromatids pulled apart to opposite poles of the cell by spindle fibres.
what happens in telophase
-Two new nuclear membranes form.
-two new nuclei form
- in animal cells Cleavage furrow starts to form (where plasma membrane starts to invaginate or fold inwards) whereas in plant cells, a cell plate begins to form.
what happens in cytokinesis
Division of the cytoplasm in the parent cell which leads to the formation of the two daughter cells that are genetically identical to each other and to the original parent cell. This occurs after mitosis.
what is checked in G1 checkpoint
Checking for DNA damage and Cell size.
what is checked in G2 checkpoint
check that DNA has correctly replicated in the S phase.
what is checked for in metaphase checkpoint
check that spindle fibres have correctly attached to the centromeres of replicated chromosomes.
what happens when an issue is found in a checkpoint
The cell will try to fix the issue (e.g. repairing DNA damage) first. If the issue cannot be fixed, then the cell will undergo apoptosis.
why can DNA double strand be easily separated
Double stranded - unwind DNA to provide template strands
Weak hydrogen bonds - easily broken to expose base pairs
Complementary base pairing - enables exact copy of DNA to be made
State the three steps in DNA replication
Step 1: DNA unwinds and unzips, separating the two strands of the DNA molecule from one another.
Step 2: Each strand then acts as a template for synthesizing a new strand of DNA.
Step 3: Two identical copies of DNA are produced
What is DNA replication
The process by which DNA makes an exact copy of itself.
What is the function of DNA
DNA controls various cellular functions by coding for functional proteins.
what is the purpose of mitosis
growth, repair, replacement
what joins sister chromatids
centromeres
what occurs in S Phase
DNA replication
semi conservative theory
a newly formed DNA molecules consists of one original strand and one newly synthesised strand
what direction does DNA polymerase move
moves 3’ to 5’
new strand synthesised 5’ to 3’
where do spindle fibres come from in animals and plants
animals-centrosome made of 2 centrioles
plants-centrosome lacks centrioles
