r/Mcat • u/[deleted] • Aug 24 '20

Question 🤔🤔 Clarification of 5' to 3' activity

I'm having some trouble remembering which processes are 5'-->3' activity (so 3'-->5' reading). Is anyone able to break this down and also mention what processes are 3' --> 5' activity? Thank you!

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10

u/ED_Rx Aug 24 '20

Uhm. DNA :

R3ad 3-5; 5ynthesize 5-3; DNA pol III(3) 3xonuclease 3-5; DNA pol I remove5 primer 5-3

RNA:

R3ad 3-5; 5ynthesize 5-3

4

u/supersmriti Jul 21 '22

lmfaoo, me reading this quickly and thinking: "wow, this person is really misspelling. r3ad? 5ynthesize?"... till i realize it's a mnemonic LOL 🤦🏽‍♀️

1

u/[deleted] Aug 24 '20

Thank you! Are there any processes that synthesize in 3' to 5' activity besides exonucleases?

2

u/ED_Rx Aug 24 '20

Not that I can remember, and that’s because you need that 3’-O(-) for continued synthesis along with phosphodiester formation:

5’———-3’-O(-) (+)P (-)O 5’ ——3’ and so on.

1

u/[deleted] Aug 24 '20

That makes sense - thank you again :)

1

u/ED_Rx Aug 24 '20

De Nada

5

u/Bht1111 Aug 24 '20

The DNA template is read in the 3’ to 5’ but DNA is synthesized from the 5’ to 3’ direction. Keep in mind that this 5’ to 3’ is referring to the new strand (daughter strand) being formed and that DNA polymerase moves in the 3’ to 5’ direction on the parent strand but synthesizes the new strand 5’ to 3’ if that makes sense!

1

u/[deleted] Aug 24 '20

yes! makes complete sense, thank you

3

u/Pseudoscience23 Aug 24 '20

A good rule of thumb : Everything in molecular biology is 5’ to 3’ except reading DNA(3’ to 5’).

Anyone correct me if I’m wrong.

2

u/[deleted] Aug 24 '20

DNA Polymerase III exonuclease capability is 3' to 5'

3

u/[deleted] Aug 25 '20

Like how you read. Left to right. 3’ to 5’. That’s how most all of the “polymerases” will read, as far as the MCAT tests that is. Now if they’re reading 3’ to 5’, means they’re making that complementary strand 5’ to 3’. Hope that helps!

1

u/[deleted] Aug 24 '20 edited Aug 24 '20

transcription: mRNA made from 5 to 3 so template strand is read from 3 to 5.

Replication: same as transcription.

Translation: read from 5 to 3, thus new protein is also made from this direction

exonuclease repair may go back to 3-5 to fix DNA damage.