Biology help understanding

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Yazomi
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#1
Report Thread starter 1 year ago
#1
In mitosis

What’s the difference between chromosomes, Chromatids, DNA and homologous pair?

What becomes which when it’s unravelled or condensed- also just double checking condensed is the opposite of unravelling right?

Currently I my understanding
at the start of mitosis, DNA unravel. - into homologous pairs( 2 chromosomes) /chromosomes.
Chromosome line up in the centre and sister chromatids pulled to opposite ends of the pole (kinda like a quarter of a homologous pair?)

Chromatids uncoil?? Tho this part I don’t really get. I though it should be condensed here. Why does it need to uncoil. And why uncoiling chromatids become chromosomes??
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CreasedAirForces
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#2
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#2
Finally a question I can answer!

- Chromosomes are 2 Sister Chromatids held together by a centromere.
- Chromatids are basically half of a chromosome.
- There are many different definitions for DNA, under the A-Level AQA spec, its's "Deoxyribonucleic acid. Composed of nucleic acids, these molecules encode the genes that allow genetic information to be passed to offspring." So think of all those nucleotides in a double stranded chain.
- A homologous pair are basically a pair of chromosomes with the same loci (position), gene sequence (order of bases) etc.

Mitosis has 5 Key stages - Interphase, Prophase, Metaphase, Anaphase, Telophase

Interphase is where DNA replication occurs and the organelles in the cell double
Prophase is where the nuclear envelope breaks down and the chromosomes condense and become visible
Metaphase is where the chromosomes line up along the equator of the cell, and spindle fibres (2 from each pole) attach to the centromeres
Anaphase is where the spindle fibres retract and separate the sister chromatids, pulling them to opposite poles of the cell
Telophase is where 2 nuclear envelopes form (around the separated chromatids on each pole of the cell) and cell membranes form around them. The DNA starts to uncoil here
Cytokinesis occurs after, think of it as the physical separation of the daughter cells, pulling them apart from each other after the cell membrane reforms around them both

Uncoiling only occurs during the telophase, after cell division. This is so that the DNA can perform its usual cell tasks of making pre-mRNA etc... The DNA then coils and forms chromatids through Prophase to Telophase, it never uncoils during mitosis, this might be what you were confusing it with.

Uncoiling chromatids does not form chromosomes, because chromosomes are made of chromatids.

This may sound confusing when written down, try watching this Amoeba Sisters video linked below - they tend to explain things better:

https://www.youtube.com/watch?v=f-ldPgEfAHI - (Skip to 2:25)
Last edited by CreasedAirForces; 1 year ago
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Yazomi
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#3
Report Thread starter 1 year ago
#3
(Original post by CreasedAirForces)
Finally a question I can answer!

- Chromosomes are 2 Sister Chromatids held together by a centromere.
- Chromatids are basically half of a chromosome.
- There are many different definitions for DNA, under the A-Level AQA spec, its's "Deoxyribonucleic acid. Composed of nucleic acids, these molecules encode the genes that allow genetic information to be passed to offspring." So think of all those nucleotides in a double stranded chain.
- A homologous pair are basically a pair of chromosomes with the same loci (position), gene sequence (order of bases) etc.

Mitosis has 5 Key stages - Interphase, Prophase, Metaphase, Anaphase, Telophase

Interphase is where DNA replication occurs and the organelles in the cell double
Prophase is where the nuclear envelope breaks down and the chromosomes condense and become visible
Metaphase is where the chromosomes line up along the equator of the cell, and spindle fibres (2 from each pole) attach to the centromeres
Anaphase is where the spindle fibres retract and separate the sister chromatids, pulling them to opposite poles of the cell
Telophase is where 2 nuclear envelopes form (around the separated chromatids on each pole of the cell) and cell membranes form around them.
Cytokinesis occurs after, think of it as the physical separation of the daughter cells, pulling them apart from each other after the cell membrane reforms around them both

Uncoiling only occurs during the interphase, after cell division. This is so that the DNA can perform its usual cell tasks of making pre-mRNA etc... The DNA then coils and forms chromatids through Prophase to Telophase, it never uncoils during mitosis, this might be what you were confusing it with.

Uncoiling chromatids does not form chromosomes, because chromosomes are made of chromatids.

This may sound confusing when written down, try watching this Amoeba Sisters video linked below - they tend to explain things better:

https://www.youtube.com/watch?v=f-ldPgEfAHI - (Skip to 2:25)
Ahhhhhhhhh that makes a lot more sense thank you very much!!!

Just double checking- is uncoiling during interphase is condensing into chromosomes or uncoiling of the DNA helix?
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CreasedAirForces
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#4
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#4
Technically the uncoiling actually starts in the telophase, and the DNA is fully uncoiled by the time the interphase starts again. Think of it like a repeating cycle.

The uncoiling is another way of saying uncondensed. When we talk about uncondensed DNA, we mean that it is no longer visible as chromatids and chromosomes. (So no chromosomes in interphase). But the structure of DNA remains as a double helix. So imagine DNA being twisted and then coiled again, like a telephone cable. Check the image below, it'll show it better.

https://www.shutterstock.com/image-v...ose-1640805628

Name:  ezgif.com-gif-maker.jpg
Views: 15
Size:  66.3 KB
[Ignore the yellow spheres (histones), they are proteins, they aren't that important, just note how the DNA looks uncondensed/uncoiled]

In short, uncoiling happens in telophase and then it coils/condenses in prophase for mitosis
Last edited by CreasedAirForces; 1 year ago
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Yazomi
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#5
Report Thread starter 1 year ago
#5
(Original post by CreasedAirForces)
Technically the uncoiling actually starts in the telophase, and the DNA is fully uncoiled by the time the interphase starts again. Think of it like a repeating cycle.

The uncoiling is another way of saying uncondensed. When we talk about uncondensed DNA, we mean that it is no longer visible as chromatids and chromosomes. (So no chromosomes in interphase). But the structure of DNA remains as a double helix. So imagine DNA being twisted and then coiled again, like a telephone cable. Check the image below, it'll show it better.

https://www.shutterstock.com/image-v...ose-1640805628

Name:  ezgif.com-gif-maker.jpg
Views: 15
Size:  66.3 KB
[Ignore the yellow spheres (histones), they are proteins, they aren't that important, just note how the DNA looks uncondensed/uncoiled]

In short, uncoiling happens in telophase and then it coils/condenses in prophase for mitosis
Ohhhhhhhhh this makes so much more sense now thanks once again!! Love the details!!
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