1. DNA and chromosome structure Flashcards
Types of nucleic acids
- DNA
- RNA
Building blocks of nucleic acids
- Phosphate Group
- Nitrogenous Base
- Sugar
Two kinds of sugar are:
- Ribose (in RNA)
- 2-Deoxyribose (in DNA)
Difference between Ribose and 2-Deoxyribose:
- OH Group is present on 2’ Carbon of Ribose.
- No Oxygen present on 2’ Carbon of 2-Deoxyribose.
Two kinds of Nitrogenous Base:
- Purines
- Pyrimidines
Purines are:
- Adenine (A) and Guanine (G)
- AGGIES
- Purine ring = two rings
Pyrimidines are:
- Cytosine (C), Uracil (U), Thymine (T)
- CUT
- Pyrimidine Ring = one ring
Nucleic Acid Building Block
Phosphate Group components:
- One Phosphate
- 4 Oxygens: One double bonded O. One single bonded O. Two single bonded O-.
Nucleosides are:
- Sugar + Nitrogenous Base
- Nucleoside + Phosphate Group = Nucleotide
Nucleic Acids
What are Nucleic Acids:
String of nucleotides bound by PHOSPHODIESTER BONDS
Nucleic Acids
Phosphodiester Bonds:
Bonds from 3’ to 5’ end.
* 5’ CH2 - Phosphate group end.
* 3’ C - OH end.
Nucleic Acids
What happens when phosphodiester bonds are formed:
Diagram on Slide 14
- 5’ Phosphate group end binds to 3’ OH group.
- OH on phosphate group + 3’ OH + Condensation reaction = Phosphodiester bond.
- A phosphodiester linkage connects the 5’-phosphate group and the 3’-OH group of adjoining nucleotides. H2O byproduct.
Slide 14
Triphosphate Nucleotides are:
Diagram on Slide 15
Precursors to growing chain of nucleic acids.
* 5’ end always gets added to 3’ end in a growing chain.
* Energy is released when 5’ phosphate end is added.
Slide 15
Nucleic Acid Structure
Primary Structure of Nucleic Acids:
Sequence of nucleotides bound by phosphodiester bonds
* 5’ to 3’ orientation
Nucleic Acid Structure
Secondary Structure of Nucleic Acids:
Determined by interactions between Nitrogenous Bases
* Hydrogen bonds between bases of complementary strands
* G-C = Three bonds
* A-T = Two Bonds
3 Types of Ribonucleic Acid (RNA)
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)
mRNA:
- FORMED during GENE TRANSCRIPTION in NUCLEUS
- Template for protein synthesis
- mRNA is link between DNA information and protein production
DNA information is found where?
In the genome, NUCLEUS
Protein Production is where?
The Cytoplasm
tRNA purpose:
- TRANSLATES nucleotide sequence into protein sequence
- Match codons with amino acids.
tRNA Structure:
- Anticodon attaches to corresponding codon.
- Anticodon SEQUENCE reads 5’-3’. Same for codon sequence.
- Has an amino acid on 3’-OH group
Ribosomes formed by:
- Proteins (~35%)
- RNA (65%)
Ribosomes have two subunits:
- Large subunit (50S)
- Small subunit (30S)
DNA Primary Structure:
- Double stranded
- Antiparallel chains/strands
- Two strands held together through hydrogen bonding between nitrogenous base pairs. (A and T = 2 Bonds) (C and G = 3 Bonds).
- The two strands are called complementary.
What would be easier to break?
* The interaction between nucleotides in the same strand
* The interaction between complementary nucleotides in opposite strands
The interaction between complementary nucleotides in opposite strands.
Two strands of DNA can be separated if necessary. Why?
Allows DNA to be:
1. Replicated
2. Transcribed
Both processes require partial separation of the two strands.
Why is it harder to break a strand of DNA?
- Protects the sequence of nucleotides from being altered.
- Protects genetic information contained in sequence.
DNA Secondary Structure:
- Two chains coiled around central axis. Double Helix.
- Nitrogenous bases lie perpendicular to axis. STACKED on one another.
- Each turn = 10 BP per chain.
- Minor and Major grooves.
Chromatin
Histones:
- DNA Packaging through formation of NUCLEOSOMES
- A set of proteins
- FIVE TYPES: H1, H2A, H2B, H3, H4
Why do you think Histones are rich in positively charged residues like lysine?
The positive charges allow them to closely associate with the negatively charged DNA through electrostatic interactions.
* The negatively charged DNA is wrapped around positively charged histone.
Nucleosomes:
- A section of DNA that is wrapped around a core of proteins (HISTONES).
- Formed when the negatively charged DNA surrounds the histone octamers
Nucleosomes = Octomers
Histone octamer is the eight-protein complex found at the center of a nucleosome core particle
* a nucleosome is an octamer because it is composed of eight histone proteins
Heterochromatin
- Very COMPACT and DENSE DNA
- Mostly formed by: Regions of genome with NO GENES or Genes that are PERMANENTLY REPRESSED
- Most of Y Chromosome is in here.
- Centromeres and Telomeres DO NOT have genes on theme. Made of Heterochromatin.
Euchromatin
- Chromatin is MORE RELAXED
- Allows genes to be TURNED ON AND OFF
What would happened if a gene that is being expressed Is relocated to Heterochromatin
* It would stop being expressed and it could not be turned on
* It would stop but it could still be turned on
* Nothing, It would continue being expressed
It would stop being expressed and it could not be turned on.
