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Chapters 16 ( Molecular basis of inheritance) and 17 (Gene Expression From…
Chapters 16 ( Molecular basis of inheritance) and 17 (Gene Expression From gene to Protein
Chapter 17
Gene Expression: Process of DNA directing the synthesis of proteins and sometimes RNA's
RNA Processing
Occurs in all organisms and within the nuclear envelope. Occurs during interphase
Enzymes modify the two ends of a eukaryotic pre mRNA molecule. When the mRNA reaches the cytoplasm, the modified ends, as well as certain cytoplasm proteins, facilitate ribosomal attachment.
5'end
3' end
RNA Splicing
Introns
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where large portions of RNA molecules are removed and the remaining portions are reconnected.
an enzyme then adds on 50-250 more adenine nucleotides forming a poly- A tail.
Synthesized first and receives a 5' cap or modified form of guanine
Translation: the synthesis of a polypeptide using the information in the mRNA.
Occurs in all organisms and on ribosomes. Occurs during interphase..
Basic concept
tRNA
Anticodon
Aminoacyl-tRNA synthetases
Carries out the correct matching up of related enzymes
the nucleotide triplet that base-pairs to a specific mRNA codon. In order for the tRNA molecule to fit its function.
Transfer RNA is the translator. It is supposed to transfer an amino acid from the cytoplasmic pool of amino acids to a growing polypeptide in a ribosome.
An mRNA molecule is moved through a ribosome, codons are translated into amino acids one by one. The translators or interpreters are tRNA molecules each type with a specific anticodon at one end and a corresponding amino acid at the other end. A tRNA adds its amino acid cargo to a growing polypeptide chain when the anticodon hydrogen bonds to the complementary codon on the mRNA
Small complexes that facilitate the linking of amino acids into polypeptide chains.
Beadle and Tatums experimental approach
Purpose: obtain nutritional mutants by exposing Neurospora cells to X-Rays, inducing mutations.
3 Each surviving cell formed a colony of genetically identical cells
Cells were subjected to X- Rays to induce mutations
Individual Neurospora cells were placed on complete medium
Cells From each colony were placed in a vial with minimal medium, Cells that did not grow were identified as nutritional mutants.
Cells from one nutritional mutant colony were placed in a series of vials, each containing minimal medium plus one additional nutrient.
Vials were observed for growth. In example 17.2 , cells only grew in minimal medium + arginine, showing that the mutant was missing the enzyme for the synthesis of arginine.
Transcription: the synthesis of RNA using information in the DNA.
Occurs in all organisms and within the nuclear envelope. It occurs during interphase. Creates pre mRNA
Template Strand
Codons
Coding Strand
RNA Polymerase
Promoter
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Enzyme that pries the two strands of DNA apart and joins together RNA nucleotides complementary to the DNA template strand, elongating the RNA polynucleotide
Non template DNA strand. It is called the coding strand because the codons are complementary to the template strand except they have a T in place of a in the mRNA.
mRNA nucleotide triplets. (UGG, ACC)
Only one of two DNA strands is transcribed. The one that is, is called the template strand. It provides the pattern or template, for the sequence of nucleotides in an RNA transcript.
mRNA is complimentary to its template strand, rather than identical because RNA nucleotides are assembled on the template according to base-pairing rules.
The nuclear envelope is a lipid bilayer that is separating the nucleus from the rest of the cell
Bacteria do not have nuclei therefore therefore nuclear membranes do not separate bacterial DNA and mRNA from Ribosomes and the other protein - synthesizing equipment. This allows Translation to of an mRNA to begin while transcription is still in progress
Chapter 16
The Structure of DNA
Each DNA nucleotide monomer consists of a nitrogenous base (A,T, C, or G)
The phosphate group of one nucleotide is attached to the sugar of the next covalent bond, forming a backbone of alternating phospates and sugars from which the bases project. .
It contains the information of genetic inheritance due to the linear sequence of nucleotides in DNA. Each molecule of DNA is a double helix formed from two complementary strands of nucleotides held together by hydrogen bonds.
This is the only way that viruses can live. They inherit the genetic information from the host and replicate themselves based off of that genetic material, they receive from the DNA. This is why its so hard to treat an infected individual, that has a virus.
Difference between DNA, Chromatin, Chromosomes
Chromatin
Under the microscope, chromatin looks like beads on a string. The beads are called Nucleosomes
Each nucleosome is composed of DNA wrapped around eight proteins called histones
Complex of DNA and protein that forms the nucleus if eukaryotic cells
DNA
DNA is made of basically nitrogenous bases ( Adenine, Thiamine, Cytosine, and Guanine).
When The bases are formed the arrange a specific segment called a gene. If they are coiled in a form that can be easily duplicated, they are known as chromosomes
Chromosomes
DNA is packaged into chromosomes
These are basically structures that carry genetic information
DNA together with proteins forms a chromosome. A chromosome is basically a chain of DNA that is made compact enough to fit a cell
There are 23 pairs of chromosomes in one set inherited by each parent
DNA replication
Semiconservative model
The two strands of the parental molecule separate and each functions as a template for synthesis of a new, complimentary strand.
Dispersive model
Each strand of both daughter molecules contains a mixture of old and newly synthesized DNA
Conservative model
the two parental strands reassociate after acting as templates for new strands thus restoring the parental double helix
Basic Concept
The parental molecule has two complimentary strands of DNA. Each base is paired by hydrogen bonding with its specific partner.
First the two DNA strands are separated. Each parental strand can now serve as a template for a new, complementary strand.
Nucleotides complementary to the parental strand are then connected to form the sugar phosphate backbones of the new daughter;
DNA replication and Repair
Replication is essentially the copying of DNA
origins of replication are sites where DNA replication begins. They are short stretches of DNA that have specific sequence of nucleotides
At the end of each replication bubble is a replication fork or a Y shaped region where the parental strands are being unwound.
Helicases are the enzymes that are unwinding the double helix at the replication forks.
Single strand binding proteins then bind to the unpaired DNA strands, keeping them from re pairing
Topoisomerase is an enzyme that helps relieve strains by breaking, swiveling, and rejoining DNA strands
The initial nucleotide chain that is formed during DNA synthesis is a short stretch of RNA, not DNA. This RNA chain is called a primer and is synthesized by primase.
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Repairing DNA
Mismatch nucleotides sometimes evade proofreading by a DNA polymerase. Mismatch repair is designed to remove and replace incorrectly paired nucleotides that have resulted from replication errors.
Nuclease cuts out or excises, a segment that contains the damaged DNA
When the enzymes are a DNA ligase and a DNA polymerase it is called a nucleotide excision pair
An important function of DNA repair enzymes in our skin cells is to repair genetic damage caused by ultraviolet rays of sunlight.
