DNA structure and chromosomes Flashcards
what are the three parts of nucleic acids?
pentose sugar
nitrogenous base
phosphate
what are the two types of pentose sugars?
DNA
RNA
what are the two types of nitrogenous base?
purine
pyrimidine
what are the bases considered purines?
guanine
adenine
what are the bases considered pyrimidine?
cytosine
thymine
uracil
what is the difference between RNA and DNA?
the type of chemical group bound to the 2’ carbon
RNA= OH
DNA= H
what is a nucleoside?
molecules of a sugar and a base
what do Deoxyribonucleosides consist of?
2 deoxyribose sugar and a nitrogenous base
where does a base bind on a deoxyribonucleoside?
carbon 1 of a deoxyribose/ribose
what are nucleotides?
a nucleoside molecule and phosphate
where does the phosphate group attach on a nucleotide?
carbon 5 of the deoxyribose/ribose
what is DNA?
a polymer of deoxyribonucleotides
how do nucleotide monomers polymerize?
by phosphodiester bonds
where do covalent bonds form in the pentose phosphate backbone?
between phosphate and the c-3 and c-5 of two pentose sugars
why is DNA polar?
because the 3’ end has an OH which differs from the 5’ end
what did chargaff study?
overall quantities of the four nitrogenous bases in various organisms
what is Chargaffs rule?
%A=%T; %C=%G
what are 3 conclusions of Chargaffs rule?
%purines= %pyrimidines
C+G does not equal A+T
C, G, A, T aren’t present in equal amounts
what evidence suggested
what is DNA associated with?
proteins and organized into structures called chromosomes
what is chromatin?
a given region of DNA with its proteins on a chromosome
what are 2 shapes of chromosomes?
linear
circular
what is a plasmid?
small circular independent DNA
where are plasmids in the cell?
the cytoplasm
what type of chromosomes do prokaryotes have?
one circular chromosome and plasmids
what type of chromosomes do eukaryotes have?
linear chromosomes enclosed in the nucleus
why are plasmids independent?
they carry genes that are not essential for every day life
what are histones?
positively charged proteins that DNA wind around
what are 3 reasons why DNA is organised into chromosomes?
to fit into the cell
to protect the DNA from damage
easier cell division
what are origins of replication?
DNA sequences along chromosome which
initiate DNA replication
what is the centromere?
DNA sequences required for correct segregation of chromosomes by directing formation of the kinetochore in which the mitotic spindle attaches
what are telomeres?
DNA sequences located at the ends of the chromosome that that prevent degradation and allow proper replication of the chromosomal ends
what is ploidy of eukaryotes?
diploid
what does homologous chromosomes refer to?
two copies of each chromosome
what eukaryotic cell is haploid?
sexually reproductive cells (sperm and egg)
how do parental strands unwind?
by breaking hydrogen bonds between bases
