A1.2 nucleic acids Flashcards
DNA
deoxyribonucleic acid is made of a double helix of antiparallel strands of nucleotides which are linked by hydrogen bonds between complementary base pairs
DNA is the genetic material for all living organisms, contains the genetic information for growth and development
A1.2.1 genetic material of viruses
some viruses use RNA as their genetic material but they are not considered to be living
characteristics of a living organism
MR H GREN
Metabolism
Reproduction
Homeostasis
Growth
Response
Excretion
Nutrition
nucleotides
- phosphate
- nitrogenous base
- deoxyribose (DNA), ribose (RNA)
- hydrophilic backbone on outside (sugar-phosphate)
- hydrophobic bases on inside (nitrogenous)
covalent bonds within nucleotides and between nucleotides. carbon 3 on one pentose of a nucleotide is covalently bonded phosphate of another nucleotide as a result of condensation reactions, water molecule is produced.
differences between DNA and RNA
- DNA has two strands, RNA is a single strand
- DNA has thymine as one of the bases, RNA has uracil
- DNA has a deoxyribose sugar, RNA has a ribose sugar
- DNA has a double helix shape, RNA has a variety of shapes
- DNA acts as permanent genetic code of a cell, RNA does not contain permanent genetic code
nitrogenous bases
DNA:
purines: larger, 2 carbon-nitrogen rings
- adenine
- guanine
pyrimidines: one carbon-nitrogen ring
- thymine
- cytosine
RNA:
purines:
- adenine
- guanine
pyrimidines:
- uracil
- cytosine
sequence of nitrogenous bases in a nucleic acid codes for specific proteins, each triplet (3 bases) codes for an amino acid
directionality of RNA and DNA
enzymes involved in DNA replication and transcription process can only add nucleotides in the 5 to 3 direction
C-5 of a nucleotide is added to the C-3 end of the previous nucleotide.
DNA replication
Helicase enzyme unzips the DNA, open area of DNA= replication fork, replication process is semi-conservatice ie. for each new DNA molecule made, half the original DNA strand is conserved (old), half is new
ribosomes move from 5 to 3 during translation
translation= production of polypeptides by ribosomes using mRNA genetic code. The 5 end of mRNA enters the ribosome, it moves along the mRNA molecule and translates it in a 5 to 3 direction
tetranucleotide hypothesis (falsified)
falsified by chargaff
stated that DNA is made of repeating units of A,T,G,C and that DNA strands contain equal ratios of the 4 bases
hershey-chase experiment
bacteriophages were grown in different medias. one batch was grown with radioactive sulfur 35S which was incorporated into phage protein. second batch was grown with radioactive phosphorus which was incorporated into phage DNA. The labelled bacteriophages infeced a bacterium E.coli. They were agitated in a blender to separate the phages outside the bacteria and centrifuged to separate the virus from the bacteria. The bacteria formed a pellet at the bottom of the test tube, and the virus formed a supernatant. Results showed that the supernatant in the 35-labelled bacteriophage was radioactive and the pellet in the 32-labelled bacteriophage was radioactive which concluded that DNA was responsible for hereditary material.
nucleosome
DNA (negatively charged) wrapped twice around a core of 8 histone (positively charged) proteins, held together by an additional histone protein (H1) attached to linker DNA
chargaff’s rule
falsified the tetranucleotide hypothesis.
DNA contains the same number of adenine as thymine nucleotides, as well as the same number of guanine and cytosine nucleotides
the importance of chargaff’s rule
showed that proportion of adenine to thymine and guanine to cytosine was equal but it also falsified the tetranucleotide hypothesis
