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DNA Structure & Function. Biology 12. Functions of DNA. Controls cellular functions Central Dogma – DNA makes … DNA (replication) RNA (transcription) Protein (translation). DNA. DNA. Central Dogma of molecular biology!. RNA. RNA. Protein. Protein. Structure of DNA.

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DNA Structure & Function

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DNA Structure& Function

Biology 12


Functions of DNA

  • Controls cellular functions

  • Central Dogma – DNA makes …

    • DNA (replication)

    • RNA (transcription)

    • Protein (translation)


DNA

DNA

Central

Dogma

of molecular

biology!

RNA

RNA

Protein

Protein


Structure of DNA

  • Made of nucleotides

  • Double helix

    • Two parallel strands wound around each other

    • Like a twisted ladder


What is a Nucleotide?

  • Each is made up of:

    • 1 deoxyribose sugar (a 5 carbon sugar)

    • 1 phosphate group

    • 1 of 4 nitrogenous

      bases


Like a Twisted Ladder …

  • Sides:

    • Made of alternating sugars & phosphates

    • “Sugar phosphate backbone”

  • Rungs:

    • Made of base pairs


DNA Runs Antiparallel

Parallel but in opposite directions

5’ end of one strand of DNA aligns with 3’ end of the other strand


What is a 5` & 3` end?

  • Carbons of a deoxyribose sugar are numbered 1 to 5

    #1 - attaches to nitrogenous base

    #3 - attaches to phosphate

    group ENTERING

    deoxyribose sugar

    #5 - attaches to phosphate

    group EXITING

    deoxyribose sugar


Complimentary Base Pairing

  • Pairing of nitrogenous base on one strand with the corresponding nitrogenous base

    • adenine (A) always pairs with thymine (T)

    • guanine (G) always pairs with cytosine (C)


Hydrogen Bonds

  • Base pairs held together by weak hydrogen bonds

    • 2 between A&T

    • 3 between G&C

  • Why do they need to be weak?


Pyrimidine

Single ring

Thymine (T) & Cytosine (C)

Purine

Double ring

Adenine (A) & Guanine (G)

Pyrimidine vs. Purine (#5 pg216)


Goldilocks Rule!

Why do you think the bases match up this way?

Purine + Purine = toobig

Pyrimidine + Pyrimidine = toosmall

Purine + Pyrimidine = just right!


#2 – Page 216

  • Purine & Pyrimidine always bond

  • Why can’t A-C and G-T form pairs?

    • Incorrect number of hydrogen bonds required


Rule of Chargaff

  • Amount of A = T

  • Amount of G = C

  • Why was this important to the discovery of DNA?


#6 – Page 216

  • 20% = Thymine

  • Determine % of other bases

    • 20% = A

    • 60% remains, so:

      • 30% = G

      • 30% = C


How to Read a DNA Strand

  • Start at the 5` end

    • CGAT

  • Start at 3’ end for complimentary strand (opposite strand)

    • GCTA


#3 – Page 216

  • DNA template:

    • 5’ ATGCCTTA 3’

  • Determine complementary strand:

    • 3’ TACGGAAT 5’


Short Video

DNA Structure


5’

thymine

guanine

3’

5’ end

adenine

3’

cytosine

3’

5’


Reading the DNA

3’

5’ end

DNA Template:

5’ C A G T 3’

Complimentary Strand:

3’ G T C A 5’

3’

5’


Any Questions so far?


Draw a DNA Molecule

  • Create the sequence:

    • TAC CAG GGC ATC

  • Show:

    • Directionality (3’ and 5’ ends)

    • Hydrogen bonds

  • Create a legend


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