What What What!? The end of this unit? Well, one more down, umm... 12 to go. Embarrassing, considering the amount of time I've been working on this,false starts and all.
Unit three test tomorrow, unit four test (aiming for a week from tomorrow) and then, a midterm. I'll be a third of the way through the course. It will be awesome. The pace needs to be picked up though, my scheduled college classes begin in May.
Of course, the rough endoplasmic reticulum is studded with ribosomes... and we all know the ribosomes are active in protein synthesis. ;) According to my biologist friend, the ribosomes on ER are for mRNA translation only.
Quick review:
Nucleotide: Biological building blocks for DNA and RNA. DNA: Made of a Phosphate, a 5-carbon deoxyribose sugar (a pentose sugar) and a base. One of Four bases (listed in the order they pair in)- Adenine, Thymine, Guanine and Cytosine. FOR RNA: Adenine, Thymine, Guanine and Uracil. Bases are either purines or pyrimidines. Purines are Adenine and Guanine. They have a double ring structure. Pyrimidines are Cytosine, Uracil and Thymine. These have a single ring structure.
DNA: Deoxyribonucleic acid. Our genetic material. Looks like a twisted ladder but it is actually a Polymer of nucleotides joined in the middle (hydrogen bonds) with complementary base pairing. reproduces semi conservatively.The uprights of the ladder are sugar-phosphate-sugar-phospate pattern structure. DNA must replicate with a high degree of accuracy, be able to store information and undergo mutations to control both the development and metabolic activities of the cell and organism.
DNA replication: occurs in the nucleus of the cell. 3 steps: 1. Unwinding: DNA Helicase comes in and unzips [the bases] by breaking the hydrogen bonds that hold them together. 2. Complementary base pairing: Free floating nucleotides pair with the unzipped, now open bases. 3. Joining: DNA Polymerase joins the paired nucleotides and thus, two strands of DNA are born- one side of the DNA's ladder is from the old polymer and the other side of the ladder is new: this is known as semi conservative replication because part of the old strand is always preserved. DNA replicates in this way so that it can replicate with a high degree of accuracy.
RNA: Ribonucleic acid. Structurally the same as DNA with a phosphate, a pentose sugar (ribose) and a nitrogenous base. Adenine, Guanine, Uracil and Cytosine. SINGLE STRANDED IN STRUCTURE. Functions in the synthesis of proteins. Three different tyes of RNA: tRNA: escorts amino acids to mRNA during protein synthesis rRNA: has a structural role, forming most of the ribosome, along with protein. mRNA: messenger RNA carries a coded sequence of bases to the ribosomes for protein synthesis.
Triplet codes: During protein synthesis, amino acids are carried to mRNA dependent which bases are represented and in which order. If you were to supply a singular base at a time, there would not be enough bases to code for all 20 amino acids that must link together to make proteins. By having bases available in triplets, there are enough bases available to code for 64 different bases (this includes start and stop codons). Multiple triplets can code for one amino acid.
Transcription: a strand of DNA is copied to make a strand of mRNA. During Transcription, a segment of the DNA unwinds and unzips (thank you, helicase) and ONE strand of the DNA is copied from the transcription bubble. Complementary nucleotides pair with the DNA bases using the following bases: Uracil, thymine, guanine and cytosine. A strand of mRNA results.
Translation: Translation is the process where the sequence of codons formed during transcription becomes the order of amino acids in a polypeptide.Translation begins with rRNA, coming from the nucleus and joining with a protein to form a ribosomal subunit. Then, the process of translation begins with 1.Initiation: mRNA bonds to two ribosomal subunits. 2. Elongation: tRNA brings amino acids to the ribosomal subunit/mRNA sandwich. These amino acids are the anticodons to the codons on the mRNA. The ribosomal unit has room for two tRNAs. One goes in, bearing an amino acid. That tRNA receives an amino acid chain from the tRNA just leaving the ribosome. That tRNA adds its amino acid and elongates the chain in this manner, passing the chain to the next tRNA to enter the ribosome 3. Termination: A stop codon is encountered on the mRNA. The protein drops off as the ribosome dissociates. Polyribosomes can sometimes form and they all work together along the same mRNA and create multiple copies of the same protein.
Where transcription copies the sequence of bases from the DNA string to form mRNA, translation translates these base codons to become amino acid polypeptides (protein).
Mutation: A mutation is a change in the nucleotide sequence of a gene.
Point mutation: A change in a specific nucleotide. When one base is substituted for another along the mRNA, different things can happen. There can be a silent mutation where, by luck of the draw, the nucleotide changed ends up coding for the amino acid that was needed in the first place. A Nonsense mutation happens where the codon is changed to become a Stop codon. This makes the resulting protein too short and useless. There is finally, a missense mutation. A missense mutation happens when the codon is a useful amino acid, but it is in the wrong place, affecting the shape of the resulting protein as well as the polarity. This missense mutation is what causes sickle cell disease. Valine is substituted for glutamate along the protein chain.
Frameshift mutation: An error on the reading frame or sequence of codons presented for protein synthesis occurs. A base is DELETED along the chain and shifts the codons all down one slot. This deletion changes the entire sequence of codons and confuses the entire meaning of the resulting protein. Frameshift mutations frequently result in severe genetic diseases such as Tay-Sachs disease.
Mutagens: Environmental factors that cause mutations. Mutagens cause cancer and birth defects. Radiation (Xrays) or Organic chemicals (pesticides and compounds in cigarette smoke) are mutagens. Mutations in the body cells will result in cancer. Mutations in the gametes will cause deformities in the offspring.
Recombinant DNA: Recombinant DNA contains DNA from two or more different sources. rDNA is used to create products that would be difficult to obtain by natural harvesting in mass quantities. These products are things like insulin, hormones, lung surfactant and enzymes.
To make rDNA: A vector is chosen. In the example here, we will use a bacterium. We remove the plasmid (small DNA molecule) from the bacterium and use resriction enzyme to cleave a space for the gene we want to replicate (insulin, for example) we then isolate the gene for insulin and remove it (again, using the restriction enzyme) the insulin gene is placed into the plasmid and is then sealed together as one unit using DNA ligase. The host cell (bacterium) takes up the recombined plasmid. As the host cell reproduces, the plasmid is reproduced as well, resulting in multiple copies for the rDNA. The resulting rDNA is inspected and if it is found suitable, the product [in this case insulin] is retrieved for use.
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