Nucleic acids Flashcards
What is a gene?
A segment of DNA that codes for a particular protein
Where in the cell are chromosomes located?
Nucleus
In what organelles is DNA found?
Mitochondria and chloroplasts
Which bases bond together and how?
adenine bonds with thymine using 2 hydrogen bonds
cytosine bonds with guanine using 3 hydrogen bonds
What is the structure of a nucleotide?
A pentose sugar (deoxyribose) attached to a nitrogen containing base and a phosphate group
Which bases are purine and which bases are pyramidine?
Purine = adenine and guanine - 2 rings
Pyramidine = cytosine and thymine - 1 ring
How is the structure of DNA related to its function?
Long molecule/coiling - compact so can store a large amount of genetic information
Sugar-phosphate backbone - bound by relatively strong phosphodiester bonds
Bases in sequence - the sequence of bases determines the mRNA molecule transcribed from it, which in turn determines the primary structure of the protein
Complementary base pairing - holds together the polynucleotide strand when not being transcribed or replicated, allows information to be replicated/transcribed as new DNA or RNA nucleotides can join to the exposed bases
Hydrogen bonds allow chain to split easily - for replication/transcription (1st stage of protein synthesis)
Helical structure - protects hydrogen bonds and helps to make the molecule stable
How does semi-conservative replication occur?
- 2 strands of DNA replicate and DNA helicase breaks the hydrogen bonds between complementary base pairs breaks
- the free nucleotides are attracted to their complementary base pairs in exposed bases on the template strands
- once the new nucleotides have lined up, they are attached by the enzyme DNA polymerase in a condensation reaction which joins adjacent nucleotides
- finally, all the nucleotides are joined to form a complete polynucleotide chain using DNA polymarase. This creates 2 identical strands of DNA. As each strand retains half of the original DNA material, this is called semi-conservative
How did meselson and stahl describe semi conservative replication through centrifugation?
- generation 0 has only the original polynucleotie, containing only ‘heavy’ Nitrogen 15, so each strand has a high density and therefore moves to the bottom of the centrifuge tube
- the bacteria is then transferred to a medium containing only the ‘light’ isotope of nitrogen 14. These hybrid DNA molecules are of intermediate density so move to the middle of the tube
- generation 2 has 2 hybrid DNA molecules which are of intermediate density so band in the middle of the tube . 2 DNA molecules are of low density as they only contain nitrogen 14, so form a band at the top of the tube.
- generation 3 has 2 hybrid DNA molecules which band in the middle of the tube. There is a greater proportion of low density DNA molecules, so the band of nitrogen 14 at the top of the tube is thicker
What is the structure of a nucleotide?
contain a pentose sugar, a nitrogenous base and a phosphate group
What are the bonds between nucleotides in a polynucleotide chain called?
phosphodiester bonds
What bases does RNA consist of?
adenine, cytosene, guanine and uracil
What is tRNA?
a form of RNA which has a clover-leaf structure formed when bases within an RNA molecule form complementary base pairs with other specific bases within the same molecule through the formation of hydrogen bonds. In RNA, adenine pairs with uracil, and cytosene pairs with guanine
What are ribosomes made from?
RNA and proteins
What are the roles of DNA and RNA?
DNA - holds genetic information
RNA- transfers genetic information from DNA to ribosomes
