The Cell Cycle - B9 Flashcards
Why does DNA replication occur?
replace, repair, growth
Why does DNA replication occur before the nucleus divides?
to ensure all daughter cells have the genetic information.
What is the semi-conservative model of DNA replication?
where 1 strand is new and 1 strand is original
State the steps in semi-conservative DNA replication.
1)DNA helicase unwinds the DNA ->breaks the H bonds
2)both strands act as a template
3)free DNA nucleotides join their complementary bases as A-T and C-G ->these nucleotides use active transport as they require energy
4)DNA polymerase joins the nucleotides using phosphodiester bonds
5)each new DNA molecule made of one new strand and one original strand(making two new polynucleotides)
What does the Neselson and Stahl experiment have to do with nitrogen?
-every base in a nucleotide contains nitrogen
-nitrogen is found in two main isotopes
-14N(light)
-15N(heavy)
Describe the Nesleson and Stahl experiment.
-14N(normal form of Nitrogen)
-15N(heavier isotope)
-the DNA came from bacteria
-cells grown in a 14N solution will create a band at the top of a test tube when centrifuged as they are the least dense
-cells grown in 15N solution will create a band at the bottom of the test tube when centrifuged as they are the most dense.
1)take cells from 15N and allow them to grow in a 14N solution. When centrifuged, it will create a band in the middle that is 1/2 15N and 1/2 14N
2)take cells from the second solution and allow them to grow in 14N solution. When centrifuged, there is the middle band of both and a top band of only 14N, both the same width.
3)Grow again in 14N solution, when centrifuged again, the top 14N band gets larger, but the middle band stays the same width.
-the middle band will always be there because 15N are template strands - the top strand only gets bigger.
-if DNA replication was conservative, there wouldn’t be a middle band.
What is the chromosome number?
the number of different chromosomes possessed by a species
true or false: mitosis is a eukaryotic process.
true
What is a chromosome defined as?
an independent DNA molecule
What is the S phase of the cell cycle?
DNA synthesis -> semi-conservative replication
What is the first G phase of the cell cycle?
growth -> cell grows, makes more cytoplasm
what is the second G phase of the cell cycle?
growth and preparation for mitosis->growth and preparation for mitosis ->duplicate organelles - ATP reserve
What is the M phase of the cell cycle?
Mitosis - cell division
What is cytokinesis in the cell cycle?
cell membrane splits, cytoplasm splits
What are haploid cells?
cells with one copy of each chromosome
-often gametes
What are diploid cells?
cells with two copies of each chromosome
-the two copies of a chromosome are known as homologous chromosomes
What is the difference between unduplicated and duplicated chromosomes?
no. of chromosomes is the same, but the amount of DNA increases
What is a chromosome made from?
A chromosome is made up of two sister chromatids, still joined at the centromere ->only called a chromatid when it is chromatidS(duplicated)
What is mitosis?
-Mitosis is cell division in eukaryotic cells.
-each new cell contains a complete copy of the parent cell as well as some of it’s cytoplasm
What are the results of mitosis?
genetically identical cells
what are the reasons for mitosis?
growth, repair, replace old cells(known as senecance).
What happens in interphase?
-DNA is replicated
-DNA is randomly arranged-> no spindle fibres to organise
Describe mitosis.
Prophase:
1)nuclear membrane breaks down
2)chromosomes condense ->shorter/fatter and tightly wound
3)centrioles start to make spindle fibres
Metaphase:
4)chromosomes line up in the middle of the cell/equator
5)spindles latch to centromeres
Anaphase:
6)centromeres divide
7)spindle fibres contract/shorten and pull chromatids to poles
Telophase:
8)nuclear envelope reforms
9)chromatids unwind
Cytokinesis - cell membrane and cytoplasm split
What causes the development of a tumour?
When cell division isn’t controlled,(the gene may have undergone a mutation-leading to different proteins being formed), cell division can go out of control and cells continue to divide. This results in the development of a tumour.
