UNIT C (CELL DIVISON, GENETICS, MOLECULAR BIOLOGY) Flashcards
Cell Cycle
The sequence of stages through which a cell passes from
one cell division to the next.
Mitosis
A type of cell division in which a daughter cell receives
the same number of chromosomes as the parent cell.
Chromosome
A threadlike structure of nucleic acids and proteins found in the nucleus of most living cells, carrying genetic information in the form of genes.
Chromatin
The combination of DNA and protein that make up
chromosomes.
Centromere
The structure that holds chromatids together.
Sister Chromatids (NON-Homologous Chromosomes)
A chromosome and its duplicate, attached to one another by a centromere until separated during mitosis.
Homologous Chromosomes
Pairs of chromosomes in a diploid organism that have similar genes, although not necessarily identical. Carries same genes at the same location and carries different forms (alleles) of the same gene.
HUMAN FEMALES HAS HOMOLOGOUS CHROMOSOMES WHILE MEN DO NOT.
Diploid
Refers to twice the number of chromosomes in a gamete.
Haploid
Refers to the number of chromosomes in a gamete.
Polyploid
Stages of Mitosis
- Interphase
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
Interphase (LONGEST phase)
The time interval between nuclear divisions when a cell increases in mass, roughly doubles the cytoplasmic components, and duplicates its chromosomes. Includes G1, S phase and another G2.
G1 Phase
Cells undergo a period of rapid growth, and the chromosomes are unduplicated.
S Phase
Cells begin to prepare for division during interphase by duplicating its chromosomes. At the end of the S phase, all the chromosomes are therefore duplicated chromosomes.
G2 Phase
The cell again grows and it completes the preparations for division (mitosis, or the M phase).
Prophase
- Chromosomes continue to condense. The centrioles assemble and spindle fibres attach to the centromeres of the chromosomes.
- The nuclear membrane starts to dissolve.
- The centrioles move to opposite poles of
the cell and spindle fibres start to form.
Metaphase
- Chromosomes composed of sister chromatids move toward the centre of the cell guided by the spindle fibres.
- Chromatids can become intertwined during metaphase.
Anaphase
- The centromeres divide and the sister chromatids, now referred to as chromosomes, move to opposite poles of the cell.
- Spindle fibres shorten and other microtubules in the spindle apparatus lengthen and force the poles of the cell away from each other.
- Same number and type of chromosomes will be found at each pole. One complete diploid set of chromosomes is gathered at each pole of the elongated cell.
Telophase
- Chromosomes reach opposite poles of the cell and begin to lengthen.
- Nuclear membrane forms.
- The spindle fibres dissolve.
- Chromatids start to unwind into the longer and less visible strands of chromatin.
Cytokinesis
- Cytoplasm begins to divide.
In an animal cell, a furrow develops, pinching off the cell into two parts. This is the end of cell division.
In plant cells, the separation is accomplished by a cell plate that forms between the two chromatin masses. The cell plate will develop into a new cell wall, eventually sealing off the contents of the new cells from each other.
Cell division is stopped by…
Cell specialization. Relatively unspecialized cells, such as skin cells and the cells that line the digestive tract, reproduce more often than do the more specialized muscle cells, nerve cells, and secretory cells.
What two cells divide endlessly?
The sperm-producing cells, called spermatogonia, and the cells of a cancerous tumour. Cancer cells divide at such an accelerated rate that the genes cannot regulate the proliferation and cannot direct the cells toward specialization.
Cloning
A clone originates from a single parent cell, and both the clone and parent have identical (or nearly identical) nuclear DNA. Considered a form of asexual reproduction.
Animal Cloning Technology Order
- Donor mouse developing cells collected
2, Single cells isolated and nucleus extracted - Unfertilized egg removed from recipient mouse
- Nucleus from donor injected into an enucleated egg
- Egg cultured in laboratory
- Cell mass is implanted in the recipient mouse
- Recipient mouse gives birth to the clone mouse (white same as the donor!)
Telomeres
Caps at the ends of chromosomes. Telomeres reduce in length each time a cell goes through the cell cyles and divides.
Cancer
As a cell begins to become cancerous, it divides more often, and its telomeres become very short. If its telomeres get too short, the cell may die. Often times, these cells escape death by making more telomerase enzyme, which prevents the telomeres from getting even shorter. In the large majority of cancer cells, telomere length is maintained by telomerase.
Meiosis
A type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction. two-stage cell division in which the chromosome number of the parental cell is reduced by half.
Prophase I
- Each pair of homologous chromosomes pair up (synapsis) (same genes different alleles)
- As the chromosomes synapse, the chromatids
can intertwine. Sometimes the intertwined chromatids from different homologues break and exchange segments in a process called crossing over - Centriole splits and parts move to opposite
- Each chromosome of the pair is a homologue and composed of a pair of sister chromatids (tetrad)
- Nuclear membrane disappears
Tetrad
A pair of homologous chromosomes, each with two chromatids. Prophase I of meiosis I.
Synapsis
The pairing of homologous chromosomes. This occurs during prophase I of meiosis and is where crossing over occurs as homologous chromosomes swap genetic material.
Why is crossing over important
Crossing over permits the exchange of genetic material between homologous pairs of chromosomes.
Metaphase I
- Homologous chromosomes attach themselves to the spindle fibres and line up along the equatorial plate.
- Chromosomes align as homologous pairs
- Spindle fibre from one pole attaches to one pair of sister chromatids in the tetrad
Anaphase I
- Homologous chromosomes move toward opposite poles. The process is known as segregation.
- Reduction Divison
- One member of each homologous pair will be found in each of the new cells. Each chromosome consists of two sister chromatids.
Segregation
Homologous chromosomes move toward opposite poles. This occurs during Anaphase I of meiosis
Telophase I
- Homolous chromosomes begin to uncoil and spindle fibre disappears.
- A membrane begins to form around each nucleus.
- Cytoplasm divides, there are now 2 cells!
- Unlike in mitosis, the chromosomes in the two nuclei are not identical because each of the daughter nuclei contains one member of the homologous chromosome pair.
End of Meiosis I
- Ends with 2 genetically different haploid daughter cells
- Each haploid cell contains only ONE chromosome (n=2)
- Homologus chromosomes (chromosome pairs) are separated into two different cells
- 2 haploid cells each with duplicated chromosomes
Before Meiosis II
Unlike with mitosis and meiosis I, there is no replication of chromosomes prior to meiosis II. Pairs of chromatids will separate and move to opposite poles
Prophase II
- Nuclear membrane dissolves and the spindle fibres begin to form.
- The centrioles in the two new cells move to opposite poles and new spindle fibres form. The chromosomes become attached to the spindle.
Metaphase II
- Arrangement of the chromosomes, each with two chromatids, along the equatorial plate. The chromatids remain pinned together by the centromere.
Anaphase II
- Breaking of the attachment between the two chromatids and by their movement to the opposite poles. 2. This stage ends when the nuclear membrane begins to form around the chromatids, now referred to as chromosomes.
Telophase II
- The cytoplasm separates, leaving four haploid
daughter cells. The chromosome number has
been reduced by half. These cells may become gametes. - Second division of cytoplasm occurs.
End of Meiosis II
- Daughter cells are still haploid but contain a single unreplicated chromosomes
- Sister chromatids have separated, haploid cells with non-duplicated chromosome
Independent Assortment
During meiosis, chromosome combinations occur at random. During meiosis I when homologous pairs line up in random orientations at the middle of the cell as they prepare to separate.
Variation occurs because…
- During prophase I exchange genes on the chromosomes.
- During metaphase I, the paternal and maternal chromosomes are randomly assorted. Although homologues always go to opposite poles, a pole could receive all the maternal chromosomes, all the paternal ones, or some combination.
- During fertilization, different combinations of chromosomes and genes occur when two gametes unite.
Gametogenesis
The formation of gametes (sex cells) in animals
Oogenesis
- Oogonia divide by mitosis and produce primary oocytes. 3 months after conception, the ovaries contain 2 million primary oocytes arrested in prophase I.
- One or a few oocytes complete meiosis I every month after puberty (ovulation). This produces a secondary oocyte and a first polar body which degenerates.
- Secondary oocyte undergoes meiosis II where it is arrested in metaphase II. When ovulated and fertilized, the secondary oocyte completes meiosis II. (if not it degenerates, producing an ootid and polar bodies).
- This produces a fertilized ovum and a second polar body which degenerates.
Spermatogenesis
- Spermatogonium/Spermatogonium undergoes mitosis during puberty and forms primary spermatocytes
- Primary spermatocytes undergo meiosis I to produce secondary spermatocytes
- Secondary spermatocytes undergo meiosis II to produce spermatids
Nondisjunction
Problem during segregation, too few or too many gametes!
- Anaphase I: Homologous chromosome pairs do not separate to opposite poles and instead one entire pair is pulled to the same pole
- Anaphase II: Sister chromatids do not separate to opposite poles and instead both sister chromatids pulled to the same pole
- Gametes with 22 and 24 chromosome depending on which cell is fertilized
Monosomy
A single chromosome in place of a homologous pair. A sex cell containing 22 chromosomes joins with a normal gamete causing zygote to become 2n = 45
- Turning Syndrome/Monosomy X (missing X chromosome)
Trisomy
There are three homologous chromosomes in place of a homologous pair. Sex cell containing 24 chromosomes joins with a normal gamete causing zygote to become 2n = 47
- Down Syndrome/trisomy 21
- Edwards Syndrome/trisomy 18
- Patau Syndrome/trisomy 13
Nondisjunction in either sperm or egg cells
- Klinefelter syndrome (inherit 2 X chromosomes and a single Y chromosome, males are sterile)
- Jacobs syndrome (inherits 1 X chromosome and 2 Y chromosomes (trisomic female).
Karyotype Charts
Obtain by mixing a small sample of tissue with a solution stimulating mitotic division. STOP division at metaphase, chromosomes are at their most condensed form and their size, length and centromere location are most discernible. Metaphase chromosomes are placed onto a slide, stained, image enlarged and each chromosome is cut out and paired up with its homologue.
Asexual Reproduction
Mitosis is the key mechanism
Sexual Reproduction
Meiosis and fertilization is the key mechanism
Prokaryotes
Different from human somatic cells, does not undergo mitosis. Bacteria and other prokaryotes have a single circular chromosome and NO nucleus, they use binary fission, grow exponentially with genetically identical populations.
Budding
Mini version of the parent grows out from the parent’s body, organism separates to be independent.
Vegetative Reproduction
Offspring develop at the end of a creeping stem (strawberry).
Fragmentation
The organism grows from a fragment of a parent plant (potatoes, sea stars).
Parthenogenesis
Unfertilized eggs develop into offspring (bees, lizards).
Spores
Structure containing genetic material and cytoplasm surrounded by protective sheath/wall. May be haploid or diploid and not all spores are the product of asexual reproduction.
Life cycle of plants consists of 2 generations…
Haploid and diploid generation
Diploid Generation
Sporophyte (spore-making body): through meiosis, the sporophyte produces one or more haploid spores.
Haploid Generation
Gametophyte (gamete-making body): through mitosis, each haploid spore grows into the plant body, producing male and female gametes while fusing at fertilization to make another sporophyte.
Allele
One of the alternative forms of a gene
Dominant Trait
A characteristic that is expressed when one or both
alleles in an individual are the dominant form
Recessive Trait
A characteristic that is expressed only when both alleles
in an individual are the recessive form
Homozygous Recessive
Having two identical copies of the same recessive allele
Homozygous Dominant
Having two identical copies of the same dominant allele
Heterozygous Dominant
Having different alleles for the same gene, the dominant allele overrules the recessive one.
Genotype
The genetic complement of an organism.
Phenotype
The observable characteristics of an organism.
Law of Segregation
During meiosis, genes seperate randomly so that each gamete has a copy of an allele for each gene.
Anaphase (I and II) of meiosis.
Law of Independent Assortment
During meiosis, chromosome combinations occur at random.
Test Cross
The cross of an individual of unknown genotype to
an individual that is fully recessive. The phenotypes of the F1 generation of a test cross reveal whether an individual with a dominant trait (such as a white ram) is homozygous or heterozygous for the dominant allele.
Monohybrid Cross
Pleiotropic Genes
A gene that affects more than one characteristic. Sickle-cell anemia, a blood disorder, is caused by a pleiotropic gene.
Multiple Alleles
When traits are determined by more than two (multiple) alleles, the most commonly seen trait is called the wild type, and the allele that determines it is the wild-type allele. Non-wild-type traits are said to be mutant, and the alleles that determine them are mutant alleles. In most cases of multiple alleles, there is a hierarchy of dominance.
Incomplete Dominance
The expression of both forms of an allele in a heterozygous individual in the cells of an organism produces an intermediate phenotype. (MIXING)
Co-dominance
The expression of both forms of an allele in heterozygous individuals in different cells of the same organism. (SEE BOTH)
Dihybrid Cross
A genetic cross involving two genes, each of which has more than one allele.
Selective Breeding, Inbreeding, True Breeding
Selective breeding: the crossing of desired traits from plants or animals to produce offspring with both
characteristics.
Inbreeding: the process whereby breeding stock is drawn from a limited number of individuals possessing desirable phenotypes.
Polygenic Traits & Barr Bodies
Inherited characteristics that are determined by more than one gene. Each of the genes can have multiple alleles, show incomplete dominance or co-dominance, and can be affected by the environment.
A small, dark spot of chromatin located in the nucleus of
a female mammalian cell.
Epistasis
A gene that masks the expression of another gene or
genes.
Linked Genes
Genes closer will be less likely to seperate than genes far, therefore genes closer will have a higher chance of being transferred together to a new cell. Alleles of 2 different genes on the same chromosome do not assort independently.
**The closer two genes were to one another on a chromosome, the greater their chance of being inherited together. In contrast, genes located farther away from one another on the same chromosome were more likely to be separated during recombination.
**
the larger the distance between two genetic loci, the greater the chance that they will be separated by a crossover
Marker Gene
A gene that confers an easily identifiable phenotype and
is used to trace the inheritance of other genes that are difficult to identify; it must be located on the same chromosome, and ideally, at a very small distance from the gene being followed.
Autosome
A chromosome not involved in sex determination.
Sex-linked Trait
Trait that is determined by genes located on the sex chromosomes.
Chromosomes & Humans
Humans have 46 chromosomes (44 autosomes and 2 sex chromosomes). 2 pairs of homologous autosomes and 1 pair of sex chromosomes.
Men (XY): Do not contain same gene and are not homologous
Women (XX): Do have a homologous pair (hence 23 homologous pairs).
Pedigrees
A chart used to record the transmission of a particular trait or traits over several generations.
Identifying a DOMINANT pedigree
Trait DOES NOT skip generation. Affected people have an unaffected child.
Identifying a RECESSIVE pedigree
Trait SKIPS a generation. Unaffected people have affected kids.
Identifying an X-linked RECESSIVE pedigree
Only boys are affected, females rarely affected.
Identifying an X-linked DOMINANT pedigree
Father has it and all girls are affected, males are still affected. Sometimes, males who have a disorder 0% chance of passing to sons.
Identifying Autosomal RECESSIVE pedigree
Both genders are affected (affect males and females equally).
Identifying Autosomal DOMINANT pedigree
Father has it and not all girls are affected (affect males and females equally).
People who contributed to DNA findings
- Friedrich Miescher (1869): white blood cells from wounded soldiers, named ‘“nucleic acid” or “nuclein,” composed of acidic portion and alkaline portion (protein), DNA and RNA
- Pheobus Levene (early 1900s): isolated 2 types of nucleic acid, chromosomes made up of DNA and protein, genes are on chromosomes, rules of DNA and RNA
3: Fredrick Griffith (1928): studies pathogenic bacteria, transforming principle (S and R cells) - Oswald Avery, Colin MacLeod and Maclyn McCarty (1944): continued with Griffith’s experiment, concluded DNA is the transforming factory NOT protein (many still didn’t believe)
- Alfred Hershey and Martha Chase (1952): used radioactive bacteriophages, only DNA from the bacteriophage and not protein coat entered the bacteria
- Rosalind Franklin (1950): X-ray photography, DNA was a helix double-stranded, nitrogen bases inside helix and sugar-phosphate is outside
- James Watson and Francis Crick (1953): Used stolen info.
DNA
Hereditary material, five carbon cyclic structure (deoxyribose sugar) phosphate group, one of four nitrogen-containing bases (adenine, guanine, cytosine and thymine).
We are different from other humans and other organisms due to
Different DNA nitrogen sequences. An individual’s DNA is unique except in identical twins. DNA in the cell nucleus is the genetic material inherited from our biological parents.
RNA
Also A, G, C but instead of T there is a U, base uracil instead of thymine.
A pairs with G…
purines
C pairs with T…
pyrimadines
Why was Levene wrong
Believed nucleotides were present in equal amounts and appeared in chains in a constant and repeated sequence.
Chargaff’s Rule
Found that nucleotides not present in equal amounts, amount of adenine = thymine and amount of cytosine = guanine.
DNA Model
Nitrogen bases in the middle, deoxyribose sugar molecule, phosphate molecule outside. Hydrogen bonds, between the complementary bases (A-T and G-C) on opposite strands, hold the double helix together.
Antiparallel
Parallel but running in opposite directions; the 5 prime end of one strand of DNA aligns with the 3 prime end of the other strand in a double helix.
DNA Replication
The process whereby DNA makes exact copies of itself.
Semiconservative Replication
Process of replication in which each DNA molecule is composed of one parent strand and one newly synthesized strand.
Template
A single-stranded DNA sequence that acts as the guiding
pattern for producing a complementary DNA strand.
DNA helicase
The enzyme that unwinds double-helical DNA by
disrupting hydrogen bonds.
Primase
Synthesises an RNA primer to begin the elongation process.
DNA Polymerase III
The enzyme that synthesizes complementary
strands of DNA during DNA replication.
DNA Polymerase I
Replaces RNA primers and fills in the gaps once the primer is gone.
DNA ligase
Connects Okazaki fragments in the lagging strand.
Initiation (DNA REPLICATION)
- Helicase unwinds the helix by breaking the hydrogen bonds
- Two strands are now separated along part of the DNA molecule and are the template strands for the next step in replication
- The point at which the two template strands are separating is called the replication fork. One template strand runs in the 3 prime to 5 prime direction in relation to the replication fork, while the other runs in the 5 prime to 3 prime direction
Elongation and Termination (DNA REPLICATION)
- 2 new DNA strands synthesized on template strand through complementary base pairing
- DNA polymerase III adds complementary nucleotides to the growing strands, using the exposed strands of the parent DNA molecule as a template.
- The leading strand is formed continuously.
- The lagging strand is formed in short fragments, starting from an RNA primer.
- DNA polymerase I cuts out the RNA primers and replaces them with the appropriate DNA nucleotides.
- DNA ligase joins the fragments together to form a complete DNA strand.
Repair and Termination (DNA REPLICATION)
- Both DNA polymerase I and III act as quality control checkers and proofread new strands
- Rewind into helix structure
- Termination, completing of 2 new DNA strands and dismantling of the replication machine
Gene expression
Conversion of a gene into a specific trait through
the production of a particular polypeptide. The products of all genes are polypeptides.
Genetic code
The order of the base pairs in a DNA molecule determines how amino acids are strung together and how proteins are made. The order of the nucleotides ina gene provides the info to build a protein.
RNA
A nucleic acid consists of nucleotides comprised of the sugar ribose and nitrogenous bases. Messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Single-stranded, not double stranded and a polymer of nucleotides similar to DNA.
The Central Dogma
The central dogma of molecular biology is a theory stating that genetic information flows only in one direction, from DNA, to RNA, to protein, or RNA directly to protein. The two-step process of transferring genetic information from DNA to RNA and then from RNA to protein is known as the central dogma of molecular genetics.
Transcription
The process of converting DNA into messenger RNA. This takes place in the nucleus.
mRNA
The product of transcription of a gene; mRNA is translated by ribosomes into protein. mRNA carries the genetic information from the nucleus to the cytoplasm as it passes through the pores in the nuclear envelope.
Translation
The genetic information carried by the mRNA is used to synthesize a polypeptide chain. Takes place in the cytoplasm.
RNA Polymerase
Enzyme that transcribes DNA.
Initiation (TRANSCRIPTION)
- RNA polymerase binds to the DNA at a specific site near the beginning of the gene and opens the double helix.
- Sequence of nucleotides on DNA serves as promoter region where RNA polymerase will bind (TATA)
- The promoter indicates which DNA strand should be transcribed and where the RNA polymerase should start transcribing the DNA. Since the binding site of RNA polymerase only recognizes the promoter region, it can only bind in front of a gene.
Elongation (TRANSCRIPTION)
- RNA polymerase starts building single-stranded mRNA in 5 prime to 3 prime
- Similar to DNA rep but different as RNA polymerase does not require a primer and copies only one of the DNA strands, no need for Okazaki fragments
- Enzymes synthesised a strand of mRNA complementary to sense strand of DNA, replacing thymine with uracil
mRNA produced…
Is a copy of the sense strand but with U’s but the antisense strand is the one being transcribed.
Template Strand (anti-sense)
Used to synthesize DNA and is where RNA polymerase is active. It synthesizes mRNA from 5 prime to 3 prime but reads DNA in the opposite direction.
Non-template strand (sense)
This is the coding strand, the sequences match with RNA except uracil is found in RNA, thymine in DNA.
Termination (TRANSCRIPTION)
- Synthesis of the mRNA continues until RNA polymerase reaches the end of the gene. RNA polymerase recognizes the end of the gene when it comes to a stop signal called a
termination sequence. - Newly synthesized mRNA disconnects from the DNA template strand & DNA double helix forms
- RNA polymerase is then free to bind to another promoter region and transcribe another gene.
Codon
Sequence of three bases in DNA or complementary mRNA that serves as a code for a particular amino acid.
Anti-codon
Group of three complementary bases on tRNA that
recognizes and pairs with a codon on the mRNA.
rNA
Part of the ribosome, or protein builders, of the cell. Ribosomes are responsible for translation, or the process our cells use to make proteins. rRNA are responsible for reading the order of amino acids and linking amino acids together.
tRNA
The form of RNA that delivers amino acids to a
ribosome during translation. Links each mRNA codon to its specific amino acid. One lobe contains the anticodon (complementary to mRNA codon) and the opposite end is a binding site for the amino acid corresponding to the codon.
Initiation (TRANSLATION)
- Ribosome recognizes a specific sequence on the mRNA and binds to that site. Made up of a large subunit and a small subunit.
- Begin reading the coding sequence at the correct place in the mRNA, or it will misread all the codons. The first codon that it recognizes is the start codon AUG.
- Uses that to produce a corresponding tRNA molecule
Elongation (TRANSLATION)
- Ribosome has 2 sites for RNA to attach, the A (aminoacyl) site and P (peptidyl) site
- The tRNA with the anticodon complementary to the start codon enters the P site
- The next tRNA carrying the required amino
acid enters the A site - A peptide bond has formed between the methionine and the second amino acid, alanine.
- Ribosome shifts over one codon so that the second tRNA is now in the P site. This action has released the methionine-carrying tRNA from the ribosome and allowed a third tRNA to enter the empty A site.
- The tRNAs that have been released are recycled in the cell cytoplasm by adding new amino acids to them. The process continues until the entire code of the mRNA has been translated and the ribosome reaches a stop codon
Termination (TRANSLATION)
- Ribosome reaches one of the three stop codons: UGA, UAG, or UAA.
- Since these three codons do not code for an amino acid, there are no corresponding tRNAs. A protein known as a release factor recognizes that the ribosome has stalled and helps release the polypeptide chain from the ribosome.
- The two subunits of the ribosome now fall off the mRNA and translation stops.
Mutation
A permanent change in the genetic material of an organism
Somatic Mutation
Mutations in body cells (KEY cause of cancer)
Germ Line Mutation
Mutations in reproductive cells (passed on!)
Point Mutation
Causes OTHER mutations. A chemical change that can affect just one or a few nucleotides.
- substitution
- deletion
- insertion
Gene mutations change the coding for amino acids.
Silent Mutation
A mutation that does not result in a change in the amino acid coded for.
Mis-sense Mutation (SUBSTITUTION)
A mutation that results in the single substitution of one amino acid in the polypeptide. Different amino acid placed in polypeptide, therefore altered protein. May be good or bad!
Nonsense Mutation (ADDITION OR DELETION)
A mutation that introduces a stop codon into the genetic code and prevents the protein from being made completely. It is often lethal and can impact one or two nucleotides.
Frameshift Mutation (ADDITION OR DELETION)
The insertion or deletion of nucleotide bases in numbers that are not multiples of three. This affects the most, and can also be a substitution if 3 nucleotides are added or removed. This mutation alters the reading frame and can result in a nonsense mutation.
Spontaneous Mutation
A mutation occurs as a result of errors made in DNA replication.
Induced Mutation
A mutation is caused by a chemical agent or radiation.
mtDNA
Mitochondrial DNA, nucelar DNA comes from both parents while mtDNA comes only from mother. It provides clues about evolutionary history of humans, identical mtDNA means recent maternal ancestor.
Phylogeny
Proposed evolutionary history of a species or group of
organisms.
Recombinant DNA
Fragment of DNA composed of sequences
originating from at least two different sources.
- Use enzymes to cut up DNA (restriction endonucleases)
- Where it is cut is known as a sticky end or can be a blunt end
- Connected to another DNA strand uses ligase
DNA Sequencing
DNA sequencing determines the exact order of bases (A, T, C, G) in a DNA strand. The process involves isolating and, if needed, amplifying the DNA, fragmenting it, and mixing it with primers, DNA polymerase, and nucleotides. In methods like Sanger sequencing, special terminator nucleotides stop synthesis at specific points, creating fragments of varying lengths. These fragments are then separated by size and read based on their unique signals. The sequence is analyzed to produce the precise DNA code for applications like mutation detection or genome mapping.
Gel Electrophoresis
- Seperate fragments of DNA according to mass and charge
- Electric current passed through the gel allowing it to develop a positive electric charge and negative electric charge. DNA has a negative charge and will move toward the positive end.
- Smaller fragments move faster, producing a DNA fingerprint
Methylases
Methylases are enzymes that can modify a restriction enzyme recognition site by adding a methyl (—CH3) group to one of the bases in the site Important tools in recombinant DNA technology as they protect a gene fragment from being cut in an undesired location.
Methylases are used by a bacterium to protect its DNA from digestion by its own restriction enzymes. In bacteria, restriction enzymes provide a crude type of immune system. In fact, the term restriction comes from early observations that these enzymes appeared to restrict
the infection of E. coli cells by viruses known as bacteriophages. The restriction enzymes bind to recognition sites in the viral DNA and cut it, making it useless.
Polymerase Chain Reaction (PCR)
Necessary to amplify a small amount of DNA to a useable amount and usually mix with others such as gel electrophoresing. Make billions of copies of pieces of DNA from small quantities!
1. The mixture is heated to a temperature high enough to break the hydrogen bonds in the double helix of the DNA and separate the strands. This forms single-stranded DNA
templates.
2. The mixture is cooled, and the primers form hydrogen bonds with the DNA templates.
3. Taq polymerase synthesizes a new stand of DNA from the DNA template by complementary base pairing, starting at each primer.
4. The cycle of heating and cooling is repeated many times.
Plasmid
Specific type of vector used in bacteria for cloning or gene expression.
Vector
DNA molecule to transfer genetic material into a cell (plasmid, virus, or other DNA types.
DNA microarray
Going backwards!
1. mRNA is extracted from the cell or cells to be studied
2. mRNA from each cell sample is used as a template to synthesize an artificial form of DNA, called cDNA (copy DNA). The cDNA is marked by a florescent tag for later identification.
3. The labelled cDNA are incubated with the microarray. The cDNA binds to the microarray at locations corresponding to individual genes in the cell genome.
4. The microarray is scanned and analyzed to compare the patterns of gene expression in each cell sample.
Used to compare gene expression in healthy vs cancerous tissue.
Medicinal Bacteria (Insulin) Applications
Take a human cell and bacteria. Extract the insulin gene from humans and use the plasmid from the bacteria. Combine the two to produce a recombinant plasmid. Place this in the transgenic bacteria, grow in culture and extract the insulin!
Gene Therapy
A molecule called a DNA vector carries foreign DNA into target cells in the patient. A technique that uses a gene(s) to treat, prevent or cure a disease or medical disorder. Often, gene therapy works by adding new copies of a gene that is broken, or by replacing a defective or missing gene in a patient’s cells with a healthy version of that gene.
One type of DNA vector commonly used in gene therapy trials is a modified form of virus. Viruses are well suited to gene therapy because most have the ability to target certain types of living cells and insert their DNA into the genomes of these cells. Using restriction endonucleases, viruses can be genetically altered to carry a desired gene.
IS LIKE DNA REPLICATION.
what law does not apply to linked genes
Law of independent assortment, linked genes will not sort independently.
They tend to be inherited together unless crossing over happens during prophase I to break them apart.
recombination occurs in prophase 1 crossing over
what law does not apply to incompletely dominant or co-dominant alleles
Law of segregation applies only to traits that completely control a single gene pair in which one of the two alleles is overriding the other. Therefore, the law of segregation does not apply to incompletely dominant or co-dominant alleles.
CONDENSED DNA IS
CHROMOSOMES
important words in stages…
segregation, synapsis, crossing over, independent/random assortment
ploidy
- mitosis: (in telophase) count centromeres and add number (2n, 3n) based on ploidy
- meiosis I: (in telophase) count centromeres ONLY IN ONE CELL and since it is haploid, it will be n. In stages in between to find the overall ploidy since mitosis, count homologous chromosomes as ONE chromosome.
- meiosis II (in telophase) count centromeres ONLY IN ONE CELL and since it is haploid, it will be n. In stages in between to find the overall ploidy since mitosis, count each sister chromatid as one chromosome.
genes can be
turned on or off
