DNA Structure | A-level Biology | OCR, AQA, Edexcel

DNA Structure in a Snap! Unlock the full A-level Biology course at bit.ly/2TPG9Uh created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University.
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The key points covered of this video include:
1. The DNA Double Helix
2. Complementary Base Pairing
3. Antiparallel Strands
The DNA Double Helix
The structure of DNA was first discovered by the scientists, Watson and Crick. However, their discovery was based on pioneering research by Rosalind Franklin. Watson and Crick worked out that DNA was composed of two very long polynucleotide chains twisted into a double helix. The sides of the DNA double helix are made from pentose sugar and phosphate groups forming a sugar-phosphate backbone. The two strands of DNA are held together by hydrogen bonds between the bases forming the "rungs" of the DNA double helix. The double helix of DNA is also antiparallel - the strands of DNA run in opposite directions to each other.
Complementary Base Pairing
In DNA, the two polynucleotide strands are held together by hydrogen bonds between two bases. The base pairing in DNA is very specific: The correct bases pair up due to: The number of hydrogen bonds each pair of bases can form, The size of the bases - a larger purine must always pair with a smaller pyrimidine. Because the structure and bonding of the bases makes the pairing specific, we say the bases are complementary to each other. Due to base pairing, there will always be the same percentage of complementary bases in a DNA molecule. This is known as Chargaff's Rule after the scientist who discovered it.
Antiparallel Strands
The two polynucleotide strands in DNA run in opposite directions to each other - they are antiparallel. One of the strands runs 5' to 3' while the other strand runs 3' to 5'. The directions are named according to the position number of the carbon atoms in the pentose sugar of each nucleotide. In a mononucleotide, carbon five is bonded to the phosphate group and carbon three has a hydroxyl group. However, in a polynucleotide, carbon three is instead bonded to the phosphate group of the next nucleotide, creating a 5' to 3' strand. In DNA, the strands run in opposite directions, creating one 5' to 3' strand and one 3' to 5' strand.
Summary
DNA is composed of two polynucleotide chains twisted into a double helix
DNA has a sugar-phosphate backbone and bases joined together by hydrogen bonds
Adenine pairs with thymine by two hydrogen bonds and guanine pairs with cytosine by three hydrogen bonds
The two DNA strands are antiparallel, with one running 5' to 3' and the other running 3' to 5'

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[@snaprevise]

That's great to hear! We're glad you find our videos helpful! 😊

[@eman2297]

Finally understood the 5’ 3’

[@edenmarlowe2385]

thx for going into more detail on why the bases pair with each other and also for the structure of the pentose sugar, its easier to remember now that i actually know whats going on (as far as A-lv goes anyway).

[@snaprevise]

You're welcome! We're glad you liked it! 👍

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Thank you very much for explaining it. Now i understand it.👍

[@snaprevise]

You are welcome! Glad to hear that!

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[@snaprevise]

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Sir can we get pdf of these slides

[@thirsty1629]

No.

[@betul-ev2fu]

ss it

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Thanking you ❤

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[@ummamaadil4176]

Very helpful lecture

[@Anna-nw1ge]

Our body is so complex 😦 even we don't understand it well
Btw I'm the 1st one to comment 🤑

[@carlosjesus46]

Hello, first of all thank you for the amazing video and the way is explained, so helpful. I would like to ask, are there any chance to get paper document/notes to print it? I'm studying A level biology and I would like to have some physical note to make comments on it.

[@LegendaryHeroponRiki]

do we need to know how the bases bond and know the structure of them?

[@sineadscott8667]

THANK YOU

[@snaprevise]

You're welcome! 👏

[@ummamaadil4176]

I really like it

[@jbbantz5432]

Why do u call it prime?

[@deets1621]

hi so i am confused on where does an H come from in formation of H2O. Because the phosphate has O
and the C 3 ' has an OH which doesnt seem to make sense to me as two H and one O is needed

[@al-braaashraf9994]

The number of OH is in a different proportion from phosphate molecules

[@jcn268]

u taught me what 5' to 3' is. my bio teacher couldnt even teach me what it is in 2 months!

[@regicide8091]

what is 5 ' 3

[@jcn268]

@@regicide8091 5 prime to 3 prime, basically 5 carbon to 3 carbon in a deoxyribose sugar

[@betul-ev2fu]

*thanksss*

[@snaprevise]

You're welcome! ✌

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Nice

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