in this video we're going to discuss the cell cycle um so if we think about what the cell cycle is it is the period of time from when the cell is formed till the cell divides and within the cell cycle they learn multiple phases so in this video we're going to provide an overview of all of those phases with some major events that happen in each of them it is important to understand that the cell cycle happens under the control of a lot of chemical molecules such as cyclins and cyclin-dependent kinases and we are not going to look at all those details because it is beyond the scope of our class but if you are taking some advanced classes in biology perhaps you are discussing some of those molecular events so if we think of a cell cycle as a circle we can divide the cell cycle into multiple phases so the first phase that we have here and this one actually occupies most of the cell cycle so i'm going to do it in blue all of this is known as interphase right right here interface uh interface generally is the phase when the cell grows the cell produces its proteins and the cell is carrying out its functions right so uh think about uh a pancreatic cell that's responsible for making insulin is making insulin interface um a cell such as a neuron is going to produce neurotransmitters a cell in the skin like keratinocytes is going to produce keratin and so forth right so the overall function of interphase is growth protein synthesis and in addition to that carrying out the functions now interface is purpose subdivided into smaller phases the first one which is represented here one of the longer ones known as g1 okay so g1 phase where um same things that overall happen in interface are going one g1 is then followed by a phase known as the s phase and letter s stands for synthesis right so i'm going to write here g1 s which stands for synthesis and this phase gives the name because an important event happens here this event is known as dna replication what is dna replication uh when you think about this imagine we are making an extra copy of the dna we're duplicating the genome right so duplicate the entire genome of the cell why is that important well we know that a phase within the cell cycle is mitosis we're going to mark it here where the cell divides and successful mitotic division requires that the amount of dna is doubled so we can divide it equally between the offspring cells so um again dna replication uh follows a lot of molecular signaling uh lots of chemicals that are involved in valve we are not going to discuss all of those details but we are going to provide somewhat of a generalized summary of what happens during dna replication so imagine this we know the dna is a double helix right so we have two strands and we know that the strands are attached to each other with hydrogen bonds and these hydrogen bonds are formed between the complementary base pairing so a attached to t c to g and so forth well during dna replications if we want to double the amount of dna if we want to copy what we already have we are going to have to uncoil unwind and actually split those two strands of dna so indiana replication that's going to be one strand and that's going to be another strand and this place where the two strands are split is known as the replication fork so let me label it here replication fork this unwinding and splitting of dna strands is happening with the help of dna helicase so dna healthy case now once those strands are separated we are now able to create new strands based on the information that we have on the old strand right so let me mark this purple ones as the old strand now we know that on the old strand we are going to have a sequence of bases and i'm just making up some here a c t a g for example right of the same thing is going to happen on the second strand and using an enzyme that we call dna polymerase we are able to assemble a second strand because we know that according to the law of complementary base peering across from a we have t across from c we have g across from t we have a across from t a across from a t across from g c and so forth so with the help of dna polymerase we are going to create this new strands there are some details in which this two strands are formed and they're actually formed in opposite directions there are some kawasaki segments um that uh will end up connecting um some of his bases together but the idea is that at the end of dna replication we started with one dna right so this is one but we end up with two dnas and in this new dna that's formed we have an old strand and a new strand right so we're not throwing away the genetic information that we have and starting from scratch we are using the genetic information that we have to create double the genetic information so for that reason dna replication is known as semi-conservative all right semi-conservative means in this new dna one strength is old one strength is new we've preserved something that we already had to create this new one needless to say for a lot of mistakes that are being made during dna replication we have enzymes that are able to go through them and make corrections um and um if those corrections are not made we end up with what we know as mutations so dna replication is very important because in later phases we're going to see we're going to split or divide this genetic material between two offspring cells the last phase in the interface is g2 again kind of same thing happens on in g2 because it happens in g1 but in addition to that the cell is now starting to get ready for mitosis so gets ready the face that is going to follow is known as mitosis so mitosis actually has uh four of its own faces um so i'm going to divide it into four and we're going to write mitosis here mitosis is asexual division a sexual reproduction also known as somatic division and mitosis um is actually going to divide our genetic information right so as a result of mitosis we are going to have division of nucleus because that's where our genetic information is located so mitosis has four phases um they are prophase metaphase anaphase and telophase and each phase of mitosis has certain events happening throughout it we're going to discuss it in a separate video um but if we think about the purpose of mitosis so why do we need it in the body um right um mitosis is extremely important for us because one it helps us with growth and we're talking both embryonic growth because we're all at one point where one cell and then we became two then fourth and eighth and so forth it also is very important for replacing old cells or worn out cells that cannot perform their functions anymore and they are also important for healing right so if we had cells that were damaged then we can potentially replace them just a side note here not all cells um will undergo mitosis some some cells like cardiac cells and i'm going to put them here most neurons osteoblasts and so there's a variety of cells um in the voiding that are known as ammitoitic and that means they never enter mitosis right they stay in interface throughout the rest of their life and if they're damaged we cannot replace them with new cells and the last phase that we have here is cytokinesis and cytokinesis is the division of cytoplasm right so in mitosis we've divided the genetic information but then in cytokinesis we divide the cytoplasm and as a result of mitosis we create two daughter cells