Chapter 17-20 Flashcards
DNA facts
Stands for deoxyribonucleic acid
Blueprint of a cell, determines what a cell is and what a cell does.
Genetic material in a cell (passes on traits to offspring)
Controls protein synthesis
Controls cell division
Controls metabolism
DNA location
Most DNA is located in the nucleus of a cell (nuclear DNA)
Some DNA is found in the mitochondria (mitochondrial DNA)
Mitochondrial DNA is passed on only from the mother
DNA basic unit
Basic unit of DNA is the nucleotide
Nucleotide consists of
Three parts: a sugar (deoxyribose), a phosphate and a nitrogen base
4 kinds of nitrogen bases
(Also means for kinds of nucleotides)
Adenine (A), Guanine (G), thymine (T) and cytosine (C)
DNA Structure
Consists of 2 strands of nucleotides bound together, nitrogen bases of each strand form hydrogen bonds together. The 2 strands are antiparallel to each other(run in opposite directions). The 2 strands twist around each other to form a double helix
Nitrogen base pairings
A always pairs with T, and G always pairs with C. A and T are complimentary. G and C are complimentary
Genes and Chromosomes
Many base pairs linked together make a gene, that is responsible for expressing a single trait. Many genes linked together make a chromosome, chromosomes are long strands of DNA compacted into a distinct shape to conserve space. It is the unique sequence of base pairs that makes us each unique
DNA replication
Before cells can divide through mitosis or meiosis, they must make an exact copy of their DNA. Is semi-conservative meaning each strand of DNA acts as a template for a new complementary strand. For this to happen the 2 dna strands must separate and each strand will make a new strand
Enzymes required for DNA replication
Helicase, DNA polymerase, primase, DNA ligase
Stage 1 of DNA replication
An enzyme called helipads breaks down the helical shape and separates the 2 strands of DNA to form a replication fork
Stage 2 of DNA replication
Once the 2 strands are separated each one will make a new strand complementary to itself. DNA SYNTHESIS IS ALWAYS IN A 5-3 DIRECTION***
Leading strand
One strand can be synthesized continuously as the DNA strands separate
Lagging strand
The strand that cannot be synthesized continuously in DNA replication, must be synthesized in smaller pieces called Okazaki fragments. Primase makes a primer, then DNA polymerase adds free nucleotides to the lagging strand. Finally ligase connects the Okazaki fragments together.
DNA polymerase
The enzyme that adds free nucleotides to the leading strand
Primase
Enzyme that makes an RNA primer (the primer is necessary to get the process started)
Ligase
The enzyme that connects the Okazaki fragments together
Replication Machine
The complex of DNA and enzymes together, by the time the replication machine Gets to the end of the double stranded DNA, 2 identical DNA molecules have been created
Levene (1900’s)
Isolated 2 types of nucleic acid, calling them ribose nucleic acid (RNA) and deoxyribose nucleic acid (DNA). Showed that chromosomes are made up of DNA and proteins. It was not known at this time that DNA was the genetic material
Griffith (1928)
Worked with mice and with 2 strains of the bacteria, streptococcus pneumoniae, a deadly one (S strain) and a non deadly one (R strain). Experiment was important because Griffith proved the existence of a transforming factor, a chemical that can change the characteristics of a bacteria. (Genetic material)
Avery, McCarty, McCleod
Experiment was important because it provided solid evidence that griffiths transforming factor was DNA, when they treated heat killed pathogenic bacteria with a protein destroying enzyme transformation still occurred. When they treated heat killed pathogenic bacteria with a DNA destroying enzyme transformation did not occur
Hershey and Chase
Experiment was important because it showed that the genetic material was DNA and not protein, used bacteriophage viruses with a radioactively labelled phosphorus DNA. Viruses were allowed to infect bacterial cells by injecting their genetic material into them, only the radioactive phosphorus was found in the bacterial cells showing that the genetic material was DNA. Called the blender experiment because they used a blender to remove viral particles from the surface of bacterial cells.
Chargaff (1949)
Studied the composition of DNA from many species.
Rules:
For each species the amount of A is equal to the amount of T, and the amount of G is equal to the amount of C
For each species amount of purines is equal to amount of pyrmimidines (A+G=C+T)
A + T does not equal G + C, this ratio varies between species but is the same for all tissues of a single species
Franklin
Used X-ray diffraction technique to show that DNA has a helical structure
Watson and Crick- the double helix
Knew that the basic building blocks were nucleotides made up of nitrogen bases, pentode stager and phosphates.
Knew that (a and c) = (t and g)
Deduced that A always bonded to T and C always bonded to G
Deduced from X Ray diffractions that DNA was a double helix, and that each strand was held together by hydrogen bonds between purine and pyrimidines
DNA and protein synthesis
A major function of DNA is to control the synthesis of proteins in a cell, every organisms characteristics are the result of the different proteins that it’s cells make and the relative amounts of each protein they make. Protein synthesis has two major steps: transcription and translation
Ribonucleic acid (RNA)
Similar to DNA but:
Single stranded, contains the sugar ribose not deoxyribose found in DNA, contains the base uracil (U) instead of Thymine (T).
3 kinds of RNA
Messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)
Transcription
First step in protein synthesis, takes place in the nucleus, and involves using a strand of DNA as a template to make a single strand of mRNA.
Required enzyme is RNA polymerase
RNA polymerase
Finds a promoter region on the DNA that tells it where to bind. Once it binds it opens up a section of the DNA molecule, then moves along the DNA sense strand and uses it as a template to the mRNA. Once mRNA has been made it leaves the nucleus
Translation
Involves using the single stranded mRNA as a template for protein synthesis, occurs in the cytoplasm at a ribosome. Uses transfer RNA (tRNA) to transfer specific amino acids to the correct place on the mRNA
Codon
Each group of three bases in an mRNA, each codes for one specific amino acid. String of codons codes for a string of amino acids (protein)
Genetic Code
Each codon codes for one specific amino acid, the Code is redundant that is some amino acids are coded for by more than 1 codon. Is universal, is the same for all living things
Initiator Codon
AUG, codes for the amino acid methionine where the translation starts
Terminator Codons
Three terminator codons that signal the end of a protein, UGA, UAG, UAA
Mutation
Is the change in the structure of the chromosome or in nucleotide sequence of DNA molecule
Somatic cell Mutations
Occur during life time, caused by radiation, chemicals, are not inheritable
Gametic Cell mutations
Occurs in the genes of gametes, chromosomal or DNA sequence, are inheritable
Mutagenic Agents
X-rays, ultra-violet light, chemical agents (most chemical agents are carcinogenic cancer causing, they disrupt the expression of genes that regulate the cell cycle causing the cell to divide uncontrollably forming a tumour)
Chromosomal Mutations
Involve the rearrangement or even the loss of whole blocks of genes
Nucleotide Mutations
Involve changes in nucleotide sequence called point mutations, replacement of one nucleotide with another termed base pair substitution, alteration of a sequence by the insertion or deletion or both results in a reading frame shift. Reading frame shift alter all triplet groupings downstream of the mutation
Silent mutation
No effect on the polypeptide produced
Mis-sense mutation
Results in a slightly altered protein (1 amino acid) it is possible that is is still functional
Non-sense mutation
No functional protein produced
Effects of Mutations
Can cause biochemical disorders, physiological disorders, can be developmental lethals, birth defects.
*effect of the mutation depends on the gene/genes that are being affected
Cystic Fibrosis
Genetic disorder, that results from a single nucleotide mutation which leads to a defective transmembrane chloride pump. Cells in the respiratory system cannot remove enough chloride ions so they accumulate on the inside of the cells. Mucus produced lacks water making it very thick and hard to clear
Characteristics of Cystic Fibrosis
People with CF, tend to accumulate large amounts of very thick mucus in their lungs and have trouble digesting their food. Prone to infection, difficulty breathing, life expectancy 15 years, no cure
Future Treatment of Cystic Fibrosis (Gene Therapy)
Due to a mutation in a single gene, (instructions for the cell on how to make the proper protein pump), isolate the normal gene then insert copies of this gene into the affected cells to begin to make that protein and have working chloride pumps.
Gene therapy
The use of genes for correcting genetic disorders. One vector used is a virus, we can insert the wanted gene into the virus and it can insert the gene into the affected cells. Risks: the viral protein coat can trigger an immune reaction (death). A harmless virus could become pathogenic again if it comes into contact with other viruses
Somatic Gene Therapy
Therapy aimed at correcting disorders in somatic cells, this would not prevent the disorder from being passed on to the patients offspring
Germ Line Gene Therapy
Used to modify the genetic information carried in gametes, in theory this could eliminate genetic disorders. Research in this area is currently banned
Transgenic plants
Crops that contain recombinant DNA, crops can be grown to be resistant to herbicides and insects as well as frost and drought resistant and even with greater nutritional value
Transgenic animals
Inserting human genes into animals so that they would produce human products
Cloning
Making genetically identical animals
Transgenic animal examples
Goats are being used to produce pharmaceutical products in their milk, transgenic goats can produce spider silk in their milk. The silk is extracted and spun into lightweight but strong fibres.
Animal organ transplants
Research is underway to make animals with organs that have no antigens on them
Plasmid Vectors
Plasmids are small circular pieces of extrachromosomal DNA. Contain genes that give bacterium selective advantage, can be opened up using restriction enzymes. Can be moved from one bacterium to another
Steps in recombining DNA
Use restriction enzymes to cut out specific pieces of DNA containing the wanted gene, isolate the wanted section of DNA using gel electrophoresis. Insert DNA segment into a plasmid vector using restriction enzymes and DNA ligase. Plasmid vector transforms bacteria into a recombinant
Restriction Enzymes
Recognize a specific sequence of nucleotides on DNA, cleave the DNA at every recognition site sequence. In nature these enzymes allow bacterial cells to resist infection by cutting into fragments
Electrophoresis steps
- Bands of DNA fragments bearing negative charge move toward positive electrode
- Smaller fragments move more rapidly than larger ones
- Movement continues as long as electric field is maintained
Restriction enzymes and electrophoresis
Can create a genetic profile of an individual that can be used in paternity tests and in solving crimes, referred to as DNA fingerprinting or RFLP analysis. Every individual has a unique DNA sequence so restriction enzymes will cut their DNA in different places. Using electrophoresis to separate these segments of DNA will provide a unique DNA fingerprint
