Cycle 3 Flashcards
What is a genome
all of the DNA sequence in one copy of an organism’s chromosomes.
What are chromosomes
Chromosomes correspond to the # of centromeres. This means that through replication the chromosome stays as one copy
what is the n-value?
the number of unique nuclear chromosomes present in an organism. (This means that if there are two copies of a chromosomes, it doesn’t count since only the unique one matters)
Coefficient of n (ploidy)
tells us the number of uniques sets present in an organism. Ex. human has 23 unique chromosomes, but 2 total sets = 46 chromosomes
What is the C-value?
It represents the amount of DNA in one set of an organism’s nuclear chromosomes. Alternatively it can be referred to as the genome size. It refers to the quantity of base pairs of mass of the DNA (measured in picograms)
What is the coefficient of C?
It tells us how many times the entire genome is present in a cell.(you can also find it by counter the number of sister chromatids in one set)
Does the C value change during replication?
NO, only the coefficient of C changes during the cell cycle.
what is the progression of the copies of DNA
G1: One copy of DNA, S: DNA replicated, G2: two copies DNA, metaphase: 2 copies, after cytokinesis, each daughter cells ends up 1 copy
Features of the karotype
- Shown in metaphase
- one line of chromosome is two sister chromatids
What happens to the chromosomes of a diploid cell throughout the cell cycle?
The number of chromosomes stays the same at 2N. This is because in the cell cycle even though the strands of chromosomes are duplicated, to have 2 copies of the DNA. The # of centromeres stays the same, therefore the # of chromosomes has not changed and N also stays the same. The coefficient of C on the other hand changes since the genome has duplicated
Does N imply anything about C?
NO. This is due to the C-value paradox; Which is that the genome size does not dictate the complexity of the organism. Ex. axolotl, lungfish who have very high C value but are not necessarily that complex.
Why is inheritance of sameness important?
So that the protein synthesized are the same and can function properly. Thus you want to be able to replicate and copy the base pairs with a very high fidelity. Its important to note that if there inheritance of not sameness it will not always be bad, it just depends on where and how it happens.
What is the structure of the DNA
1) there is a nucleotide that consist of a 5 carbon sugar deoxyribose, a phosphate group and one of the four nitrogenous bases
2) adenine and guanine are purines
3) thymine and cytosine are pyrimidines
4) in the sugar-phosphate backbone the phosphate group makes a phosphodiester bond with the 3’ carbon of one sugar and the 5’ carbon of the next.
5) Distinct 3’ 5’ end that confer positional polarity to DNA backbones
6) 3’ end have free hydroxyl group, whereas the 5’ end has a free phosphate. Consequently polymerase can only attach bases and extend a strand in the 3’ direction
7) strands run antiparallel
What does it mean that DNA replication is semi-conservative? What enzymes help support this process?
DNA replication is semi-conservative since each strand acts as a template for the synthesis of a new complimentary antiparrallel strand.
Process…
1) DNA unwinds locally bit by bit.
2) Helicase works by separating the double stranded DNA
3) Topoisomerase supports helicase by cutting this backbone then rejoining it so that the tension from winding does not buildup
What does DNA polymerase do?
DNA polymerase works by joining nucleotides together to produce a new strand of DNA. It can only add on the 3’ OH. It is responsible for ensuring sameness through the same complimentary base pairings.
