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Genetics : 9/10. What bases are used to make DNA and RNA? How does a complimentary base pairing stabilize the DNA double helix? How is DNA structurally organized in a cell? What is “ semiconservative ” DNA replication?

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Genetics : 9/10

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genetics 9 10
Genetics: 9/10

What bases are used to make DNA and RNA?

How does a complimentary base pairing stabilize the DNA double helix?

How is DNA structurally organized in a cell?

What is “semiconservative” DNA replication?

Review of organelles that make it possible to produce a functional protein from DNA.


How is your Genetic Info turned into your unique proteins? Genetic Info is contained in a the DNA double helix of chromosomes located in the nucleus that is “transcribed” into mRNA. The mRNA is “translated” into protein in the cytosol after associating with ribosomes.

  • RNA and DNA are made of 5 kinds of “nucleotide”.
  • Each nucleotide is characterized by its unique nitrogenous “base”:
    • 5 bases: A, T, C, G or U
    • Who Gets What? ATGCDNA AUGCRNA
  • DNA forms a double helix that holds your genetic information
    • (“genes” are sections of DNA that code for specific proteins)
  • DNA is converted to mRNA (transcription)
  • mRNA is translated to protein (amino acids)
    • Proteins create “traits”-what you look like
  • RNA is single stranded because it contains Uracil not Thymine and because the ribose has a full hydroxyl:

-Uracil can’t hydrogen bond very well and hydroxyl-group also prevents double helix

  • Three RNA types: mRNA, tRNA, rRNA
what do the bases that make up dna and rna look like remember that rna has uracil not thymine
What do the bases that make up DNA and RNA look like?Remember that RNA has Uracil not Thymine!

DNA forms a double helix when complimentary bases on two strands hydrogen bond to each others bases. RNA cannot form a double helix because uracil can’t form hydrogen bonds to adenine and the hydroxyl-group of Ribose (RNA) blocks the formation of a RNA double helix ! Watson and Crick elucidated the double helix DNA structure in 1953

DNA Helix: wound onto histone proteins

Histones: wound into nucleosomes

Helix must also be “unwound” to make new DNA or RNA

DNA on nucleosomes: wound into chromatids, supercoiled, and wound onto chromatin

Chromatids and Chromatin must be unwound to make new DNA or RNA

Chromosome is a massive structure of tightly wound/compact dsDNA

Chromosomes must be unwound at cell replication

Parts of chromosomes must be unwound for RNA to be produced

Degrees of DNA Organization:

1) Primary base


2) Histones

3) Nucleosomes

4) Chromatin

5) Supercoiled


6) Chromatid

7) Chromosome

DNA is a huge molecule. All the DNA in the 10 trillion cells of your body put end to end would reach to the sun and back 65 times! How does all the DNA fit inside a tiny nuclei of a cell?


How do we organize this long strand into a structure that will fit inside a cell? Could you describe these structures from DNA to Chromosome (from smallest to largest)?

the chromosomes on my son dirk s fish analysis looked fine fish fluorescence in situ hybridization
The chromosomes on my son Dirk’s FISH Analysis looked fine“FISH= Fluorescence In Situ Hybridization”
Full Chromosomal Analysis: My Kid Dirk’s Karyotype Looked Good! Good=23 pairs and each chromosome had normal size
how is dna reproduced in the cell
How is DNA reproduced in the cell?
  • DNA is replicated in semi-conservative fashion.
  • This means it is unwound such that each original strand becomes the template for each new strand of DNA.
  • Therefore two new DNA strands and two new double-helices result from the original helix.
  • DNA Polymerase is the enzyme that replicates the DNA.
  • DNA is only replicated when needed during cell division.

Original cell with one ds DNA

Shown in blue. This cell is undergoing cell division into two new cells. The new DNA in the two new cells is shown in RED.

Semiconservative DNA replication in original cell!

Each strand of DNA is used as a “template” to make

the next strand of new DNA that becomes a new ds DNA helix.

Two new cells, each with

a ds DNA (1old/1new)

Four new cells:

Two cells contain

the original two DNA

strands (blue), two contain entirely new (red) DNA.

dna mrna protein transcription translation
DNA mRNA  proteinTranscription Translation
  • DNA  mRNA: organelle?
  • mRNA protein: organelle?
  • Nascent (new) protein  final protein: organelle?