Unit 5: DNA Structure and History Flashcards
Define
Genome
All of a cell’s genetic information
Describe the
Human Genome
46 chromosomes in total (2 sets (2n) of 23 (n=3) chromosomes)
Around 3 billion nucleotides
Around 20-25,000 genes
Define
Chromosome
One DNA molecule + all associated proteins
Compare and contrast
Prokaryotic & Eukaryotic Chromosomes
Both: Contain DNA
Proks:
* Found in cytosol / nucleoid region
* Singular
* Circular (loops back on self)
* “Naked” – fewer proteins associated
Euks
* Found in nucleus
* Multiple chromosomes present
* Linear (has ends)
* Has many associated proteins
Define
Chromatin
All of the DNA and associated proteins in the cell; may be condensed or relaxed
Chromosome = 1 DNA
Chromatin = all of the chromosomes
List
What forms may chromosomes be in?
Heterochromatin or euchromatin
Describe
Heterochromatin
Highly condensed form of chromatin
Allows separation of individual chromosomes
Does not allow access for transcription
Describe
Euchromatin
“True” chromatin – loose / not tightly condensed
Allows access of enzymes for transcription
Would get tangled if trying to separate individual chromosomes
Why must DNA be packaged/coiled?
So it all fits into the nucleus
AND
so that it is organized to either be used in transcription or separated for cell division
Describe how DNA is packaged into tight chromosomes
Note: “Chromosome” can refer to individual DNA molecules within the chromatin OR can refer to the highly condensed, super-coiled structures
From smallest to largest:
DNA coils into nucleosomes
Nucleosomes bundle to make a 30 nm fiber
The 30 nm fiber loops
The loops coil to make chromosome
Define
Histone
Protein molecules that bind to DNA and allow it to coil
Define
Nucleosome
A “ball” of DNA wrapped twice around 8+1 histone proteins
Define
Karyotype
An image that shows all chromosomes in their condensed state, organized by size
Describe the work of
Thomas Hunt Morgan
Supported the chromosomal theory of inheritance and showed that genetic information existing in the chromosomes
Did not determine whether genetic info was in the DNA or protein
Describe the work of
Frederick Griffith
Hint: Bacteria and mice
Used bacteria that had two forms: pathogenic (illness-causing) or non-pathogenic (“safe”) and infected them into mice
Found that non-pathogenic live bacteria, if mixed with heat-killed pathogenic material, would still lead to a deadly strain that would kill the mice
Concluded that the bacteria could be transformed
Define
Transformation
(related to DNA)
A change in the genes and/or physical traits of an organism due to its cells taking up DNA from its environment
Describe the work of
Hershey & Chase
Hint: radioactive sulfur and phosphorus
Used radioactive P and S (which can be detected) to grow bacteria-infecting viruses
The radioactive P would be incorporated into DNA but not proteins
The radioactive S would be incorporated into proteins but not DNA
They infected bacteria with each type of virus and found that the radioactive P entered the bacteria and the radioactive S did not
Concluded that DNA (but not proteins) were “injected” into bacteria when infected
Describe the work of
Chargaff
Analyzed the types of nucleotides found in various organisms, and found that for all organisms, the amount of T equaled A, and C equaled G
State
Chargaff’s Rule
In DNA, the amount of A=T and C=G
Describe the work of
Rosalind Franklin
Used X-ray crystallography to determine the 3-D structure of DNA was likely a helical shape
What is X-ray crystallography?
Method of crystallizing molecules and shooting Xrays at it
The angles of the X-rays bouncing of the molecules can be calculated to determine the shape of the individual molecules
Describe the work of
James Watson & Francis Crick
Used models of nucleotides, information from Franklin, and information from Chargaff to model the correct structure of the DNA molecule
List the parts of a nucleotide
Pentose (five carbon sugar)
Phosphate group (on the 5-carbon of the sugar)
Nitrogenous base (on the 1-carbon of the sugar)
List the
Key elements of DNA’s structure
There’s five you should list
-Sugar and phosphates “face” outward
-Nitrogenous bases “face” inward
-Double stranded helix
-Antiparallel
-Nitrogenous bases have specific base pairings
What pentose is in DNA?
Deoxyribose
What nitrogenous bases are in DNA?
adenine (A)
thymine (T)
guanine (G)
cytosine (C)
List / define the
Pyrimidines
One-ringed nitrogenous bases
Cytosine and Thymine
List / define the
Purines
Two-ringed nitrogenous bases
Guanine and Adenine
Define
Antiparallel
DNA strands run in opposite directions
Describe / explain
5’ and 3’
5’ = the end of DNA where the phosphate on the 5-carbon is free / not bound to another nucleotide
3’ = the end of DNA where the hydroxyl group on the 3-carbon is free / not bound to another nucleotide
This end is the…
5’ end
This end is the…
3’ end
How would this DNA strand be written?
5’-CGAT-3’
How would you write the complementary strand of DNA?
5’-ATCG-3’
State the Rule of Complementary Base Pairing
In DNA:
A always binds to T
C always binds to G
Why does DNA have complementary base pairing?
Consider the structures of each nucleotide
A purine and pyrimidine must bind to maintain the diameter of DNA
A and T each have two polar regions for hydrogen bonding
C and G each have three polar regions for hydrogen bonding
This ensures that A always binds to T and C always binds to G
