if i created this account in a hurry and posted all night only to abandon it as soon as it was over, there's your explanation.
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@cats-myelin
if i created this account in a hurry and posted all night only to abandon it as soon as it was over, there's your explanation.
i hate feeling like several people with widely different levels of functioning, self-concept, interests and priorities take turn having executive control over my life. i hate being so fickle-minded. i hate not being able to talk about this with anyone. i hate not having a coherent sense of identity that carries me from one moment, one day to the next. having no landmark, no place i can go back to. i have no memory of who i am, a mere train of thought can make me forget where i am, what i am, what matters. please help.
if i say bullshit just know it's 3 a.m. right now and i am trying to fit an entire semester of cellular biology into a few hours of study.
<The endomembrane system>
There is a crossover bio and psychiatry joke to be made here... Anyway, dissociative disorders and phenomena of the mind aside, let's dive into the physical world with the endomembrane system: a continuum starting at the outer nuclear enveloppe that includes the endoplasmic reticulum (both rough and smooth), the Golgi apparatus and the vesicles and lysosomes it produces.
Each member of this membrane system has one or more function:
The Rough endoplasmic reticulum is responsible for most of the cell's protein synthesis.
The Smooth endoplasmic reticuluum is responsible for lipid synthesis and has detoxification functions (which it shares with peroxisomes.)
Vesicles are involved in transportation of material, exchanges throughout the cell and into the extracellular matrix.
Lysosomes are specific types of vesicles, nearly a hundredth the size of the cell, in charge of breaking down cell parts, old organelles or endocyted material like bacteria... They 'digest' the excess, unwanted material.
Exploring the Golgi Apparatus
The Golgi body (inside the cell) receives proteins and lipids from the endoplasmic reticulum, modifies them by adding sugar molecules (glycosylation), sorts them, and then packages them into vesicles for transport to their final destinations—whether that be within the cell or exported outside.
The Golgi body, often referred to as the cell’s "post office" plays a crucial role in processing and packaging proteins and lipids.
Nuclear activity in your body!! REAL
Each of your cells (erythrocyte or red blood cells aside) contains a nucleus or, sometimes, multiple nucleii as is the case for muscle cells, placenta cells and hepatocytes. The nucleus is about 1/10th of the cell's size, standing at an average of 6 micrometers.
Look at this star...
It is easy to spot due to its size and double-enveloppe with holes--pores-- that is contiguous with the Rough Endoplasmic Rediculum (RER), both of which are covered in ribosomes.
The presence of a nucleus is, along with other cellular compartiments or organelles, the main difference between eukaryotic cells and prokaryotic cells. Genetic information is found in the nucleus, it is what we call genome. In eukaryotic cells, genetic information takes the form of several chromosomes whereas procaryotic cells have floating circular DNA, 1 chromosome and plasmid(s). But we'll focus on eukaryotic cells here.
The nucleoplasm, the gelatinous content of the nucleus, contains chromatin that is made of chains of nucleosomes (a unit of 4 histone proteins woven into DNA strands like beads on a string) in two forms:
Heterochromatin (width: 30nm), the very condensed version that pools at the borders of the nucleus, away from the nucleolus. Genes are silent in heterochromatin. Due to how tight it is, it does not allow expression.
and...
Euchromatin (width: 11nm), the relaxed version, loose enough that DNA can be read and transcribed into RNA.
Why make RNA and ribosomes?
Together, ribosomes with r RNA and the two other types of RNA allow the cell to make proteins based on genetic information, reading DNA. And proteins do.. everything.
The nucleolus is where r RNA (ribosomic RNA) is associated to ribosomic proteins in order to make ribosomes. r RNA makes up 80% of cellular RNA.
In the nucleus are also synthetized t RNA (transfer RNA) by RNA Polymerase III and m RNA (messenger RNA) by RNA Polymerase II. Messenger RNA holds the information that will be read or translated for protein synthesis in the Rough Endoplasmic Reticulum.
But not yet! It needs to undergo maturation by splicing: introns--which do not code--are removed from pre-mRNA and only introns (coding for proteins) remain.
From there, transfer RNA's ending, its 3-nucleotide anticodon, is affixed to mRNA so it can check that mRNA codons are coding for the right amino acids for the corresponding protein.
Transfer RNA reads mRNA and check its information accuracy. It is called 'transfer' because it is also responsible for transportation of amino acids to ribosomes whose rRNA work on assembling amino acids based on the 'message' of mRNA.
This entire process is how proteins are made, by translation of DNA.
Most of protein synthesis occurs in the rough endoplasmic reticulum. (here ↓)
Soon enough they'll undergo post-translational modifications...
On Mitosis
I don't know a lot about mitosis aside from the fact that it occurs after the Interphase and once DNA has been replicated, and that it is a continuous process but is divided into four stages: prophase (from the greek pro- before), metaphase, anaphase and telophase.
During prophase, chromatin is in its condensed form: heterochromatin. During metaphase, chromosomes are pushed to the center of the nucleus. Following metaphase, there is migration during the anaphase, when microtubules that make up the mitotic spindle separate chromatides and pull them to either sides of the nucleus. In the final phase, the telophase, microtubules progressively disappear, sister chromatides are decondensed and the contraction of myosine and actine filaments splits cytoplasm for cell division.
<DNA replication>
A process that happens in the nucleus during the S-phase of the Interphase (after G1 and G2), prior to Mitosis (cell division and subsequent reproduction).
Four main enzymes are involved in DNA replication.
Firstly, you'll find heligase splitting the two strands of the double-helix by breaking the hydrogen bonds between complementary bases.
Primase allows DNA-polymerase, the enzyme that is reproducing the DNA, to start working in the right location. Polymerase then copies DNA in the 5' (five prime) to 3' direction. These numbers refer to the carbon atoms that are positioned clock-wise on the nucleic acid molecule.
To respect directionality, there are gaps between segments of DNA on the lagging strand. The gaps are fixed by ligase, which bounds the segments, called 'Okazaki fragments' together.
DNA replication is semi-conservative:
Each double-helix coming out from replication is made from one original strand of DNA and a fresh one, that was replicated.
Bi-directional:
Occurring on both the leading and lagging strand at the same time.
& Follows complementary base pairings:
New bases are only paired with their complementary base in the A=T and C=G fashion.
Once replicated, DNA receives epigenetic marks. It undergoes chemical modifications aiming at preserving cell identity and regulating gene expression (these marks affect DNA-protein interactions.)
i am testing this out