Module 7 Flashcards
Central Dogma of the transfer of biological information
DNA-> RNA-> Nucleic acid sequence
must be translated into an amino acid sequence >Protein
Three nucleotides
= 1 codon
= 1 amino acid
The chemical structure of DNA
● DNA is a polymer of nucleotides
● Nucleotides are phosphorylated nucleosides
● Nucleosides comprise a ribose sugar and a nitrogen base
● There are four common nitrogen bases; two with purine ring structures (adenine and guanine) and two with pyrimidine ring
structures (thymine and cytosine)
● Nucleotides are attached by the deoxyribose sugar through phosphodiester bond
● The order or sequence of nucleotides in the DNA polymer is the code for information storage
2 DNA chains are held together by H bonds , 3 bonds between C-G and 2 between A -T. Forming a double helix. The phosphate on the 5’ and sugar on the 3’
Anti parallel complementary double helix
semi-conservative -preserves intact the two halves of the parental DNA molecule
Polarity on DNA
-polarity based on the phosphodiester backbone
● Positions on the base are indicated by a number
● Positions on the sugar are indicated by a number with a prime (‘)
●DNA strands have 5′ to 3′ polarity
conservative- produces 2 DNA helices one with old DNA and the other with all new DNA
Semi conservative - produces 2 DNA helices one strand with old and one strand with new
dispersive - produces 2 helices with alternating old and new
DNA Replication
- A new DNA strand is polymerized in the 5′ to 3′ direction, reading the parent strand in the 3′ to 5′ direction
● Leading strand, runs in 3’ to 5’ direction – DNA replication proceeds in continuous manner
●Lagging strand, runs in 5’ to 3’ direction – replication apparatus will jump a short distance and then copies backwards making small fragments called Okazaki fragments
● Helicase unwinds and unzips the DNA double helix cutting and re-closing of the DNA sugar-phosphate backbone
●Primase builds an RNA primer for the DNA polymerase to start connecting the phosphate to sugar of the incoming nucleotide
●on the lagging strand, primase will repeatedly work to start each Okazaki fragment
●another enzyme will remove RNA primer and replace it with complimentary DNA bases
●DNA polymerase brings in and free complementary nucleotides
●Ligase ties together the Okazaki fragments by form phosphodiester bonds
Enzymes involved in DNA Metabolism
DNA Polymerases
Helicases:
Primase
Methylases:
Deaminases
Ligases:
● DNA Polymerases: catalyze the formation of phosphodiester bonds to extend the3’ ends of existing DNA chains. They require a DNA template in order to determine which base to add
● Helicases: unwind and untangle double-stranded DNA
● Primase: synthesizes a short ribonucleic acid (RNA) to prime DNA synthesis
● Methylases: add methyl groups to nitrogen bases
● Deaminases: remove amine groups from nitrogen bases
● Ligases: catalyze formation of a single phosphodiester bond between two adjacent nucleic acid fragments. Seals gaps and join two shorter pieces of DNA into one longer piece
DNA-Metabolizing Enzymes
Nucleases
Exonucleases: remove bases from the ends of DNA strands
Endonucleases: cut DNA strands internally
Restriction endonucleases cut double-stranded DNA
Recombination
●mixture & assembly of new genetic combinations
● Gene cloning is a method of in vitro recombination
● Recombination occurs in vivo by crossing over and then random assortment of chromosomes
Gametes will merge to form new diploid individual.
Recombinants
● Molecule that holds the new combination of DNA sequences
● produced in eukaryotes through
sexual reproduction
● produced in prokaryotes by gene
transfer through conjugation, transduction, or transformation
Plasmids
Plasmids are used to move genes from cell to cell
● Required to perform recombinant DNA technology:
o Plasmid vectors: for carrying DNA
o Restriction enzymes: for cutting DNA
o DNA ligase: for “pasting” DNA
3 ways DNA can be transferred between bacterial cells
- Conjugation – DNA is transferred between bacteria through a tube between cells
- Transduction – DNA is accidentally moved from one bacterium to another by a virus
- Transformation – bacterium takes up a piece of DNA floating in the environment
Gene
●ordered sequence of nucleotides on a chromosome that encodes a specific functional product
- Genes contain nucleotide sequences
that will be transcribed and/or
translated into protein
DNA vs. RNA
Double-stranded VS Single-stranded
* Deoxyribose sugars VS Ribose sugars
* Contains thymine VS Contains uracil
* Lasts (almost) forever VS Short half-lives
* All normal cells contain exactly
the same DNA VS Different cell type can have different RNA profiles
* Essential & always present VS Made only when needed
Types of RNA
●Messenger RNA (mRNA): take message from DNA to ribosome
● Ribosomal RNA (rRNA): part of the ribosome
● Transfer RNA (tRNA): transports amino acid to ribosome for building proteins
RNA Transcription
Initiation
● RNA synthesis begins at the promoter that tells the RNA polymerase to sit on DNA and start transcribing. The promoter has DNA sequences that let RNA polymerase attach to DNA - forming a transcription bubble to start transcribing There are -25 and -10 prokaryotic and -25 eukaryotic promoters. Because they come that may nucleotides +1 before the initiation site. In eukaryotes there is a TATA box to help RNA polymerase bind to promoters
Eukaryotes have distal elements, proximal elements before the promoter sequence. Prokaryotes dont have distal
Elongation- when the RNA strand gets longer along on strand of DNA in 3-5 direction .
Termination - RNA polymerase will keep transcribing until there are signals to stop known as termination
mRNA Processing: polyA tail, Capping & Splicing
- mRNA carry a sequence of polyadenylic acid at the 3’ end, polyA tail that help prevent RNA degradation allowing the RNA to be taken from the nuclease to be translated into a protein by ribosomes in the cytoplasm
- Capping: 5’ end is capped with a nucleotide that has a methyl & phosphate group. Marking as self
- allows mRNA to exit nucleus
- Splicing: introns are cut out and exons are brought together
