what is the genome?
a set of genetic information found in a nucleated eukaryotic somatic cell
what does DNA consist of?
nucleotides arranged into genes and chromosomes
DNA is
the structural blueprint for all genetic instructions
purines (heterocyclic compounds) are-
adenine (A) and guanine (G)
pyrimidines are-
cytosine (C) and thymidine (T)
the backbone of DNA is made of-
a phosphate group bound to pentose by a phosphodiester bond (phosphate-deoxyribose backbone)
the genetic code in the DNA is composed of how many bases
four
The phosphodiester bond and one of the four bases bind by a ____________________ to form nucleotides
a strong covalent bond
nucleotides bind to other nucleotides on the other DNA strand by ____________________
weak hydrogen bond
pentose molecules of the DNA backbone are asymmetrically joined to phosphate groups by
phosphodiester bonds
_________________ between complementary __________________ interact to stabilize and form the double helix structure.
hydrogen bonds;nucleotides
a DNA molecule is composed of
two antiparallel DNA strands held together by hydrogen bonds between the paired bases
A and T form ____ hydrgen bonds
2
G and C form ____ hydrogen bonds
3
bases can only pair if the two polynucleotide chains that contain them are __________________________
antiparallel to each other
a single strand of DNA consists of
nucleotides joined together by sugar-phosphate linkages
the asymmetry of the sugar-phosphate units give the backbone strand a definite-
directionality/polarity
DNA exists as a-
double helix with about ten nucleotide pairs per helical turn
the sugar in DNA is
deoxyribose
phosphodiester bonds are bonds that-
form between the 3'-OH groups of the deoxyribose sugar on one nucleotide with the 5' phosphate groups on the adjacent nucleotide
the 5' phosphate group of one nucleotide is bound to
the 3' hydroxyl group of the next nucleotide
the _____ end of one strand is base-paired with the ____ end of the other strand.
5' ; 3'
why do the bases in DNA have hydrogen bonds?
the hydrogen bonds between the bases can be made and broken easily, allowing DNA to undergo accurate replication and repair
what is a nucleoside?
made up of a five-carbon sugar (pentose) bonded to a nitrogenous base and are formed by covalently linking the base to C-1' of the sugar
what is a nucleotide?
they are formed when one or more phosphate groups are attached to C-5' of a nucleoside.
what is the Watson-Crick model?
the double-helix structure of DNA
what is Chargaff's rule?
amount of A = the amount of T, the amount of G = to the amount of C.
Total purines = to Total pyrimidines overall
what is denaturation?
separating/ breaking down DNA into two single strands
what is reannealing?
when two complementary strands are put back together
define chromatin
consists of DNA bound to histone and non-histone proteins
what are histones?
small basic proteins, a heterogeneous group of closely related arginine- and lysine-rich basic proteins, make up 1/4 of amino acid residues
histones-
bind tightly to the negatively charged sugar-phosphate backbone of DNA
functionally, histones-
provide for the compaction of chromatin
a chromosome is about-
1/3 DNA and 2/3 protein by mass
structure of a nucleosome:
8 histone protiens (2 of each: H2A, H2B, H3, and H4) w/ double stranded DNA wound around it
function of a nucelosome?
packaging DNA, regulate gene expression/activity
define nuclease:
an enzyme that breaks down DNA
what is formed during the progressive compaction of chromatin
higher order structures
each core histone has-
a structured domain and an unstructured amino-terminal "tail" of 35 to 40 amino acid residues
enzyme modification by _________________, __________________, or ______________ modifies the histones net elcteric charge and shape
acetylation, methylation, phosphorylation
(changes are physiologically reversible and help prepare chromatin for DNA replication and transcription)
heterochromatin is
densely packed or compacted regions of chromatin, and genetically inactive
(transcription is inhibited here because the DNA is packaged so tightly that it is inaccessible to the proteins responsible for RNA transcription)
euchromatin is-
less densely compact chromatin regions in a transcriptionally active nucleus. commonly undergoing, preparing for, or just having completed transcription.
euchromatin represents
uncoiled chromatin structures that allow RNA polymerases' and regulatory proteins' access to DNA
Telomeres:
hexametric DNA repeats (TTAGGG) found at the ends of chromosomes to protect the chromosome from degradation
Centromeres:
allow mitotic spindles to attach to the chromosome during cell activation
in order for DNA in chromosomes to replicate-
a certain nucleotide sequence acts as a DNA replication origin
(each chromosome contains many origins of replication)
kinetochore is
a protein complex that attaches the centromere to the spindle
a gene is
the complete sequence region necessary for generating a functional product
Translation
RNA ---> protein
Transcription
DNA ----->RNA