Review Set 2 Flashcards
DNA Structure
DNA is a nucleic acid made of nucleotides; 4 of them in DNA, each with a different base
Each nucleotide is made of a phosphate group covalently bonded to a pentose sugar
Nitrogenous Bases in DNA
Adenine, Thymine, Cytosine and Guanine
How are DNA Nucleotides grouped together?
by phosphodiester bonds in a 5’ to 3’ direction to form a single strand
How is double stranded DNA created?
created when hydrogen bonds form between bases (A + T and C + G) between single strands
Double stranded DNA are….
Antiparallel
Rosalind Franklin and Maurice Wilkins at King’s College (DNA structure using x-ray diffraction) contributions to DNA Structure understanding
X-ray diffraction/ X-ray crystallography using crystallized DNA molecules X-ray beams pass through crystallized DNA (for tens of hours) and diffract (spread) when they hit atoms (or other objects) and their scattering pattern is recorded on a special film The scattering pattern produces an image from which a 3D structure can be deduced
James Watson and Francis Crick at Cavendish Laboratory in Cambridge contribution to Discovery of DNA
Molecular models of DNA using all evidence available
PHOTO 51 importance
DNA is a double helix
Phosphate groups on outside of molecule (backbone)
Nitrogenous bases on inside of molecule
Nucleosome
Fundamental unit of DNA packaging – allows supercoiling of DNA into chromosomes
Core = 8 histone proteins (+ charged) with DNA molecule (- charged) wrapped twice around
Different types of sequences for DNA
- Unique (single-copy) sequences = genes (code for proteins)
-2% of genome - Highly repetitive sequences = found
between genes (form barriers of non-
coding regions between genes)
-5 to 45% of genome
-Short-tandem repeats (STR’s): form
polymorphisms (significant variation
between individuals – used to create
DNA profiles)
-Transposable (moveable = shuffle
genes) - Structural Sequences = pseudogenes (highly coiled at centromeres and telomeres)
-20% of genome
Hershey- Chase Experiments
Used bacteriophages (viruses that infect bacterial cells – made up of DNA and a protein coat) with radioisotopes (radioactive forms of elements that decay at a predictable rate – can detect these in cells)
Used radioactive phosphorus and radioactive sulfur
Phosphorus found in DNA (phosphate groups)
Sulfur found in proteins
Created one type of bacteriophage with radioactive phosphorus and another type with radioactive sulfur
Allowed two different types of phages to infect bacterial cells
RESULTS:
Bacterial cells infected with radioactive phosphorus produced new phages with radioactive DNA.
Bacterial cells infected with non-radioactive phosphorus produced new phages with non-radioactive DNA.
None of the new viruses had radioactive sulfur (radioactive phosphorus was found in the pellet)
DNA was passed on to the new viruses, and protein was NOT!
Protein is NOT the genetic material and DNA is!
DNA REPLICATION
- Helicase unzips the parental DNA molecule (breaking H-bonds between bases)
Note: in eukaryotes, gyrase and single-strand binding proteins stabilizes unzipped DNA molecules at many sites - Primase adds a sequence of RNA bases (a primer) to each parental DNA molecule at the replication origin (each parental molecule serves as a template)
- DNA polymerase III adds new nucleotides (deoxynucleoside triphosphates – two phosphates lost to provide energy for binding) to the RNA primer (at the 3’ end ONLY) to create a new complementary strand (one for each of the parent DNA molecules – A binds to T, C binds to G) Continuous in the leading strand, as Okazaki fragments in the lagging strand (moves in a 5’ to 3’ direction – adding new nucleotides to the 3’ end only!)
- In the lagging strand, DNA ligase fills the gaps between fragments (5’ to 3’)
- DNA polymerase I removes the RNA primers and replaces them with DNA nucleotides ( 5’ to 3’ direction – DNA bases left unpaired at the tip of the 5’ end after primers removed)
What does Helicase do?
unzips the parental DNA molecule (breaking H-bonds between bases)
What does Primase do?
Adds a sequence of RNA bases (a primer) to each parental DNA molecule at the replication origin
What does DNA polymerase III do?
Adds new nucleotides (deoxynucleoside triphosphates – two phosphates lost to provide energy for binding) to the RNA primer (at the 3’ end ONLY) to create a new complementary strand (one for each of the parent DNA molecules – A binds to T, C binds to G) Continuous in the leading strand, as Okazaki fragments in the lagging strand (moves in a 5’ to 3’ direction – adding new nucleotides to the 3’ end only!)
What does DNA Polymerase I do?
removes the RNA primers and replaces them with DNA nucleotides ( 5’ to 3’ direction – DNA bases left unpaired at the tip of the 5’ end after primers removed)
Meselson and Stahl Experiments
Used 2 different isotopes of nitrogen to grow bacteria (E. coli) cells (14N and 15N)
First, cultured/ grew bacterial cells in medium containing 15N (which is heavier than 14N)
After many generations, all bacterial cells contained 15N in their DNA
15N bacteria transferred to medium containing 14N
After 1 generation in 14N medium, bacteria removed and DNA isolated
Dissolved DNA in solution and centrifuged (spun around very quickly – this separates dissolved contents based on their density – more dense items sink lower in the tube, lighter items stay closer to top of tube)
14N DNA is light, so it would be found at top of tube; 15N DNA is heavy, so it would be found at bottom of tube
Results: ALL DNA in F1 (first) generation made up of one strand with 14N and one strand with 15N (all found in middle of test tube) – this shows that DNA replication IS semiconservative!
Genes are made up of…
are made up of specific sequences of nucleotides that “code” for the sequence/order of amino acids that are put together (by ribosomes) to make up each protein
DNA Sequences Determine?
The amino acid sequence of EVERY protein in a cell (its primary structure), which influences every level of protein structure after that, which determines the protein’s overall structure, which affects its ability to function properly
Process of making Proteins
DNA –Transcription–> RNA –Translation–> Protein
What is Transcription?
RNA Polymerase (and transcription factors = proteins in eukaryotes) reads genes (antisense/ template strand of DNA) and makes mRNA molecule based on code in DNA RNA is a nucleic acid (nucleotides)
Translation
making a polypeptide chain – a protein - (putting amino acids together) from mRNA
Compare DNA and RNA
DNA, RNA
Double stranded, single stranded
Deoxyribose, Ribose
Guanine, Cytosine, Adenine, Thymine (bases) and Guanine, Cytosine, Adenine, Uracil
Steps of Transcription
- Initiation
- Elongation
- Termination