Chapter 5 -> DNA and Chromosomes Flashcards
What year was the structure of DNA discovered and who are the two main people credited with the finding?
1953, James Watson and Francis Crick
Describe the typical molecule of DNA and how it is held together etc.
Two long polynucleotide chains, each composed of four types of nucleotide subunits, held together by hydrogen bonds between the base portions of the nucleotides and the backbone being held together via covalent bonds
Who are the four main people that were involved in the discovery of DNA?
James Watson, Francis Crick, Rosalind Franklin, and Maurice Wilkins
Which three people were awarded the Nobel prize for the discovery of DNA
Maurice Wilkins, James Watson, and Francis Crick
The brief story of how DNA was discovered
Crick and Watson worked together, hypothesizing and building many models while Franklin and Wilkins worked together using x-ray crystallography. Watson and Crick become aware of Franklin’s data and use that to solve the structure
How many bases are there?
4- Adenine, Thymine, Guanine, and Cytosine
What type of bond holds together the nucleotide subunits within a DNA strand?
Phosphodiester Bonds that link the 5’ end of one sugar to the 3’ end of another
How many strands of nucleotides are in DNA?
2 Strands
Guanine and Cytosine make how many hydrogen bonds between them?
3 Hydrogen Bonds
Adenine and Thymine make how many hydrogen bonds between them?
2 Hydrogen Bonds
Structure of Eukaryotic Chromosomes
- Each human cell has ____meters of DNA
- Double-stranded DNA molecules are therefore packaged into _________
- Task of packaging DNA is done by specialized ________
- 2
- Chromosomes
- Proteins
Bacteria Cells typically carry their genes on a single ______ (what shape) DNA molecule
Circular
Chromatin Definition
Complex of DNA and proteins that folds and packages the DNA
Human cells each contain ____ copies of every chromosome, one from the mom and the other from the dad
What is the name for theses chromosomes?
2
Homologous Chromosomes
What is the only non homologous chromosome pair in humans?
X and Y
How many base pairs are in the human genome?
3.2 Billion Base Pairs AKA nucleotides
What is a karyotype?
Ordered display of full set of 46 human chromosomes (think of the colorful chromosome image)
What is the most important function of chromosomes?
AKA what do they carry?
To carry genes
What is a gene?
Segment of DNA that contains the instructions for making proteins or RNA molecule
What is a genome?
The entire genetic information that is carried by an organism
How many genes are in a human?
Dr R- 20,000
Textbook- 24,000
What is Junk DNA AKA non-coding DNA
DNA that does not carry information (excess interspersed DNA)
Usefulness to cell has not yet been demonstrated
The more complex an organism is, the larger its genome- what are the faults in this claim?
Human genome can be 200x larger than yeast BUT 30x smaller than some plants
How DNA is apportioned to chromosomes differs- give an example
46 chromosomes in humans while there are 100 chromosomes in a species of carp
What is the cell cycle?
DNA molecule that has replicated and whose replicated copies have separated and partitioned equally into two daughter cells
What occurs during interphase in the cell cycle
Big Picture: Chromosomes are duplicated
Details- chromosomes are extended as long thin threads of DNA and cannot be easily distinguished (dubbed interphase chromosomes), two specialized DNA sequences-> Replication origin (where duplication of DNA begins) and Formation of Telomeres sequence at the ends of chromosomes helps to protect the chromosome
As cell cycle proceeds, DNA coils up and adopts a more compact structure, beginning the formation of mitotic chromosomes
During what phase in the cell cycle does chromosomal duplication take place?
Interphase
What do telomeres do for DNA?
Mark ends of chromosome and serve as a protective cap
What occurs during M phase in the cell cycle?
DNA coils up until it is highly condensed to the point where mitotic chromosomes are formed, and chromosomes are distributed to 2 daughter cells via the centromere allowing the mitotic spindles to attach to each duplicated chromosome to segregate the chromosomes
CHROMOSOMES ARE EASILY VIEWED HERE
What is the centromere?
DNA sequence that allowed duplicated chromosomes to be apportioned to each daughter cell
Where are interphase chromosomes found in the nucleus
They occupy specific regions such as the nuclear envelope or nuclear lamina of the nucleus so that they do not become entangled
What two categories are the proteins that bind to DNA to form chromosomes divided into?
Histones (responsible for formation of nucleosome- first level of DNA packing) and Non Histones
During what phase in the cell cycle does chromatin look like a string of DNA beads?
What are the beads on the string?
Interphase
Nucleosomes- the basic units of chromatin structure
After mitosis- where the chromosomes are tightly packed, what happens?
They unfold into a more extended form
Is all DNA packed equally tight in the interphase phase?
NO- regions that contain genes that are being expressed and more extended
What is Heterochromatin?
Most highly condensed form of interphase chromatin - most DNA here does not contain genes
It is mostly concentrated around centromere and telomeres
How does heterochromatin deactivate an X chromosome when there are two X’s present?
One of the two X chromosomes in each nucleus becomes highly condensed and the inactivated state of that X chromosome is inherited in all of the descendants of those cells
What is the first level of DNA packing?
The formation of nucleosomes which in the interphase stage look like beads on a string
What happens to nucleosomes after the first level of packing?
They are further packed to generate more compact structure
What is a nucleosome?
DNA wound around a core of histone proteins
What does the Chromatin Remodeling Complex do?
It is a protein machine that changes the structure of nucleosomes
5 Sections of Packaging DNA
Short region of DNA double helix-> Beads on a string form of Chromatin-> Chromatin fiber of packed nucleosomes-> Chromatin Fiber that is folded into loops-> Entire Mitotic Chromosome
