Nucleic Acids synthesis and DNA packaging Flashcards
what are the rules for protein and nucleic acid synthesis?
- There are a limited number of different monomeric building blocks
- Monomers are added one at a time (ATP needed, H2O released)
- Each chain has a specific starting point
- The primary synthetic produce is often modified
what are the 2 types of nucleic acids?
Deoxyribonucleic acid (DNA): C2 attached to an H group
Ribonucleic acid (RNA): C2 attached to an OH group
mRNA function
carries genetic info from DNA in nucleus to the ribosomes in cytoplasm (where proteins are synthesized)
tRNA function
matches the corresponding amino acids to the ribosomal codons - sequences of 3 nucleotides, on the mRNA strand through its anticodon region to the growing peptide chain
rRNA function
forms the core of the ribosome and catalyzes protein synthesis
what are nucleotides and their parts?
nucleotides: the building blocks of nucleic acids (DNA and RNA)
1. Sugar: Deoxyribose or Ribose
2. Nitrogen base
Purines: adenine (A); guanine (G)
Pyrimidines: thymine (T) or uracil (U) for RNA; cytosine (C)
3. Phosphate: joins sugars via phosphodiester bonds
which bases are purines?
Adenine A and Guanine G
which bases are pyrimidines?
Thymine T or Uracil U and Cytosine C
how does the covalent structure differ between RNA and DNA?
- Sugar: RNA - ribose vs DNA - deoxyribose
- One of the 4 major nitrogen bases: RNA - U vs DNA - T
what is the difference between nucleosides and nucleotides?
Nucleoside = sugar + base
Nucleotide = nucleoside + phosphate
A nucleoside is joined to one or more phosphate groups by ester linkages and thus becomes nucleotides
what are the 4 nucleoside units in RNA?
A - Adenosine
G - guanosine
C - cytidine
U - Uridine
what are the 4 nucleoside units in DNA?
Deoxyadenosine
Deoxyguanosine
Deoxycytidine
Thymidine (not necessarily deoxythymidine because T containing nucleotide is rarely found in RNA)
what are the 5 carbons of the sugar all attached to?
C1’ → base
C2- → sugar (ribose or deoxyribose)
C3’ → next nucleotide
C5’ → phosphate
what is an example of a nucleoside and nucleotide?
nucleoside: deoxyguanosine 3’-monophosphate (3’-dGMP)
nucleotide: adenosine 5’-triphosphate (5’-ATP)
what type of bond are between nucleotides?
covalent bonds (phosphodiester bonds)
what type of bonds are between the nitrogen bases?
hydrogen bonds
how do you join nucleotides together?
Covalent bonds through the 5’-phosphate group of one sugar bonds to the 3’-OH group of the next sugar
From 5’ end → 3’ end (3’end is where new nucleotides are added)
what is the 5’ end and 3’end of a nucleic acid?
5’ end: phosphoryl group attached to the 5’C atom of the sugar
3’ end: a free hydroxyl attached to the 3’C of the sugar
what are the functions of nucleotides?
- Phosphate groups hold energy: 3 high energy phosphate bonds (ie. ATP)
ATP → ADP → AMP to release energy - Signaling: ATP → ADP → AMP → cAMP
cAMP signals “hunger” and turns on enzymes that make ATP
who are key people involved in understanding the structure of DNA and what did they discover?
Erwin Chargaff: purines bind to pyrimidines (A-T and C-G)
Rosalind franklin: X-ray diffraction experiments revealed that DNA has the shape of a coiled spring or helix
In 1953, James Watson and Francis Crick deduced that DNA was a double helix
difference between purines and pyrimidines?
Structure: purines have a DOUBLE-ring structure (6-membered ring fused to a 5-member ring); pyrimidines have a SINGLE 6-membered spring structure
Size: purines are larger than pyrimidines
number of hydrogen bonds between the base pairs A-T and C-G?
Adenine - thymine/uracil with 2 hydrogen bonds; guanine - cytosine with 3 hydrogen bonds
nucleosomes and their important facts
Nucleosomes are complexes of DNA and histones (DNA wraps around the outside of the histone octamers to form nucleosomes)
nucleosomes are the basic units of eukaryotic chromosome structure (chromatin)
joined together by linker DNA to which histone H1 binds to → the histone-DNA complex has the appearance of beads on a string
Digestion of the linker DNA yields the nucleosome core particle
Nucleosomes themselves are arranged in a helical array that further compacts the DNA → further folding then generates the chromosome
histones and their structure
small, positively charged proteins associated with eukaryotic DNA that form chromatin
the 8 histones of the core particle are arranged as an octamer composed of a (H3)2(H4)2 tetramer and a pair of (H2A-H2B) dimers