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Transcription and Translation - Protein Synthesis From DNA - Biology

in this video we're gonna talk about

transcription and translation and here

is just a basic overview of these two

processes transcription is the process

by which DNA gets converted into mRNA

also known as a messenger RNA and

translation is the process of converting

the information stored in messenger RNA

and using it to build protein now if you

recall which organ now is used to make

proteins what would you say the answer

is the ribosome the ribosome is the site

at which proteins are manufactured in

the cell so we're going to talk about

that shortly but let's go over

transcription first before we talk about

translation transcription occurs in

three steps initiation elongation and

termination

now during initiation RNA polymerase

binds to the promoter region of DNA now

what is the promoter region the promoter

region is basically a sequence of DNA

and eukaryotic DNA

it's ta-ta w8 also known as the Tata box

now this sequence is located 25

nucleotides upstream of the site which

transcription begins the next thing that

RNA polymerase does is it causes the two

DNA strands to separate and during

elongation it begins to add a

nucleotides to the growing mRNA strand

that we see here thus RNA polymerase

synthesizes mRNA started from the five

prime end go into the three prime end

however RNA polymerase

it reads the DNA strand in the 3 to the

5 prime direction now there's 2 strands

that you need to be familiar with the

first one the one that's used to

synthesize mRNA is called the template

strand or the anti sense strand so

that's the one in which RNA polymerase

is active upon the other one which is

not used this is called the nan template

strand also known as the sin strand some

textbooks will call it the coding strand

because it's sequence matches up with

RNA except the fact that you're so is

fought at RNA but thymine is found in

DNA now during the last step of

transcription which is the termination

step the RNA polymerase molecule the

mRNA strand they all separate from the

DNA template strand now in this step the

poly a polymerase enzyme it caps the 3

end of the mRNA strand and this is known

as the poly a tell now also during the

beginning of transcription the 5 end is

also capped and the reason for this is

to protect the mRNA strand from being

degraded by certain enzymes at the end

of the termination step during

transcription DNA has been used to

create a pre messenger RNA strand now

this particular strand has something

known as introns and exons introns are

basically longer sequences of

nucleotides that do not code for

anything so these they must be removed

in a process known as RNA splicing now

the exons those are shorter sequences of

nucleotides and they're going to be used

to synthesize proteins

and so the axons remain but the introns

they must be removed and so now we have

a completed messenger RNA strand now

let's work on a practice problem let's

say if you're given a sequence of

nucleotides on a DNA strand and you're

asked to write the correspondent

sequence on an mRNA strand what would it

be

feel free to pause the video and try it

so if we're reading the DNA strand from

the 3 to 5 direction we're gonna have to

write the corresponding mRNA sequence in

the 5 to 3 direction so what letter

corresponds to G it's important to know

that G always corresponds to C and

vice-versa so C corresponds to G now

what letter corresponds to 8 a usually

corresponds to T but there's no T and

RNA instead a is going to correspond to

u for yourself but T in DNA corresponds

to a in RNA and so if we continue

everything else is gonna be you see a u

a u G C and so this is the mRNA strand

that corresponds to the nucleotide

sequence in DNA listed above now let's

talk about translation which is the

process of taking the information stored

on an mRNA strand and using it to

construct a protein so once the mRNA

strand is synthesized in the nucleus it

leaves the nucleus and enters the

cytosol where it interacts with a free

ribosome or one that is attached to the

rough ER now within the ribosome it's

going to inter

with a tRNA molecule or a transfer RNA

molecule now let's focus on the sequence

of nucleotides on the mRNA strand notice

that they're separated in sets of three

each set of three nucleotides represents

a codon which matches up with another

three nucleotides on the tRNA molecule

known as an anticodon and each codon

matches up with a specific amino acid

and so that's how the information stored

in the mRNA strand can be used to

construct a specific protein then we're

going to talk more about this later in

this video translation like

transcription occurs in three steps

initiation elongation and termination so

here in this picture we have a ribosome

which is composed of two subunits the

small subunit and the large subunit and

the ribosome has three active sites the

e site the P site and the a site now

during initiation we have the start

codon a ug which corresponds to the

anticodon UAC now that particular tRNA

molecule has the math I need amino acid

attached to it and this tRNA molecule it

enters the ribosome at the P site also

known as the peptidyl site where the

peptide bonds are formed now during the

second step of translation that is

during elongation another tRNA molecule

enters the a site so I'm just gonna draw

it here and during that process a

covalent bond will form between the two

amino acids that we see here highlighted

by the red circles now as the process

continues the tRNA molecule in the p

site will move to the east site

and as it does so it's going to lose an

amino acid and so what's gonna happen is

we're gonna have a growing chain of

amino acids that will leave or extend

out of the ribosome so make sure you

understand that that the tRNA molecules

they enter the a site and then they exit

from the e site and in the process the

amino acids are being joined together so

over time this polypeptide chain is

going to grow create in a protein the

last step of translation the termination

step begins when a stop codon is read

now there are three stop codons that you

need to be familiar with the first one

is you a a and then the second one is

you AG and the third one is you G a now

these stop codons also known as nonsense

codons they don't code for any specific

tRNA molecule instead when these are

read at the a site they cause a release

factor to enter the a site which causes

the small and a large ribosomal subunits

to basically disassemble so this is

where translation ends and the protein

it leaves the ribosome where it

eventually goes to the Golgi body for

further processing and modification at

the Golgi body the proteins undergo

folding where they form a specific shape

to perform a specific function and

that's basically it for this video

hopefully it gave you a good overview of

transcription and translation so that's

all I got thanks for watching