DNA structure Flashcards
Where is chromatin located?
Nucleus
When is chromatin seen in the nucleus?
When the cell is not dividing
What are the two forms of chromatin?
Heretochromatin
Euchromatin
What is the structure of euchromatin?
DNA wrapped around histone protein
to form a nucleosome
What is the structure of heterchromatin?
Nucleosomes coil up closer to each others
What form of chromatin can gene expression occur with?
Euchromatin
How do euchromatin and heterochromatin look different under a light microscope?
Euchromatin appears lighter
heterochromatin appears darker
What are chromosomes?
Heterochromatin is much more tightly packaged
to form chromosomes
When are chromosomes seen in the nucleus?
When the cell is dividing
Can gene expression occur with chromosomes?
No
What is a gene?
Section of DNA that codes for a protein
Where are genes located?
Each gene has a specific chromosomal location
What is the genome? In humans?
Entire DNA sequence
In humans this is 24 chromosomes
22 autosomes + 2 sex chromosomes
What are two examples of nucleic acids?
DNA
RNA
What is the structure of nucleic acids?
Polynucleotides - lots of nucleotides arranged linearly
What is the structure of nucleotide?
Pentose sugar
attached to a nitrogenous base and a phosphate
What is the structure of a nucleoside?
Pentose sugar
attached to a nitrogenous base
Which pentose sugar is found in DNA?
Deoxyribose
Which pentose sugar is found in RNA?
Ribose
Which carbon atom of the pentose sugar is joined to the nitrogneous base?
1’ carbon atom
Which carbon atom of the pentose sugar is joined to the phosphate group?
5’ carbon atom
What is the difference between 2-deoxyribose and ribose?
In 2-deoxyribose, 2’ carbon atom is joined to H
In ribose, 2’ carbon atom is joined to OH
What is the bond between the 5’ carbon atom and the phosphate group called?
Phosphate ester bond
What are the two types of nitrogneous bases? What do they each mean?
Purines - have two rings
Pyrimidines - have one ring
What are some examples of purines?
Adenine
Guanine
What are some examples of pyrimidines?
Cytosine
Thymine
Uracil
Which bases are found in DNA/RNA?
Adenine
Guanine
Cytosine
Which base is found in DNA only?
Thymine
Which base is found in RNA only?
Uracil
How are nucleosides named in RNA and DNA?
RNA:
base-ine
DNA:
deoxy-base-ine
How are nucleotides named in RNA and DNA?
RNA:
base-ine monophosphate
DNA:
deoxy-base-ine monophosphate
How are nucleotides joined together in DNA?
Phosphodiester bond
between 3’ carbon of one nucleotide of phosphate group of next nucleotide
What is meant by DNA being polar?
Has two distinct ends
phosphate group at one end, 3’ OH at other end
What is base pairing?
Refers to how complementary bases line up against each other
form hydrogen bonds between them
Which bases pair up with each other?
A - T
A - U
C - G
How many hydrogen bonds form between A-T and A-U?
2 hydrogen bonds
How many hydrogen bonds form between C-G?
3 hydrogen bonds
What is the secondary structure of DNA?
Two strands of DNA come together
wind around each other to form a double-helix
How do the two strands of DNA relate to each other?
Complementary
Anti-parallel
What is meant by the two DNA strands being complementary?
Their bases are complementary to each other
hydrogen bonds form between them
What is meant by the two DNA strands being anti-parallel?
Run in opposite directions
one runs from 5’ to 3’, other runs from 3’ to 5’
What type of double helix is formed in DNA?
Right-handed double helix
What is the sugar-phosphate backbone?
Refers to how the pentose sugar and phosphate line the outside of the double helix
bases are inside
How is a DNA sequence written?
Top strand - 5’ to 3’
Bottom strang - 3’ to 5’
