Final Exam Review Sheet Flashcards

Question

Gametogenesis. Oogenesis vs Spermatogenesis

Answer 1

1. Male gametes are produced by spermatogenesis in the testes o Diploid Spermatogonium (germ cells in testes) are divided by mitosis to form Primary spermatocyte. o After puberty, undergoes Meiosis I for secondary Spermatocyte. o Undergoes Meiosis II to create spermatids. o Developmental changes occur to make spermatozoa into mobile sperm. 2. Female gametes are produced by oogenesis in the ovary. o Oogonium (germ cells in ovaries) are divided by mitosis to form primary oocyte. o Primary oocyte begins Meiosis I, which arrests at Prophase I o Secondary oocyte & first polar body, ovulation occurs -----> 1 egg released each month. o Fertilization, sperm fuses with egg, as sperm nucleus is traveling to egg nucleus (Meiosis II) to develop 1 ovum and 2nd polar body.

Answer 2

In humans, presence or absence of Y chromosome determines | gender ---> XY male, XX female (sex chromosomes)

Answer 3

The key difference between autosomes (22 pairs) and sex chromosomes (1 pair) is that the autosomes contain genes that are responsible for the determination of somatic characteristics while the sex chromosomes contain genes that determine sex and sex-related characteristics of an organism. • Sex Chromosomes – pair 23-d, still considered homologs • Autosome – pairs 1-22 that are non-sex

Answer 4

Aneuploidy is the variation in chromosome number, so that an organism gains or loses one or more chromosomes

Answer 5

Loss of a single chromosome (2n-1) Turner syndrome - a condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing

Answer 6

Klinefelter syndrome is a common genetic condition where a male is born with an extra X chromosome. (XXY)

Answer 7

Down syndrome, also known as trisomy 21, is a genetic disorder caused by a chromosomal abnormality with the presence of all or part of a third additional copy of chromosome 21.

Answer 8

Sex-linked genes are those found on one of the two types of sex chromosomes, but not both (X-linked or Y-linked).

Answer 9

1. X-linked (recessive or dominant) – Many human disorders including hemophilia and colorblindness (recessive diseases). Males are more likely to be affected.. Why? Hemizygous (a single copy of allele instead of 2) 2. Y-linked (holandric, which means located on Y chromosome) Rare, relatively few genes in humans – Transmitted from father to son

Answer 10

Sex-limited inheritance occurs in cases where the expression of a specific phenotype is absolutely limited to one sex. Sex-influenced inheritance is when the sex of an individual influences the expression of a phenotype that is not limited to one sex or the other.

Answer 11

In a testcross if TWO genes assort independently (dihybrid cross) we expect a __1:1:1:1____ ratio. Null hypothesis: Two genes are unlinked. Deviation from this 1:1:1:1 suggests linkage • Linked genes – nonrecombinant & recombinant gametes are produced. They are found on the same chromosomes. • Unlinked genes are found on different chromosomes. They have 2 genes that assort into gametes independently of each other (nonrecombinant -parentals)

Answer 12

Recombination frequency = # of recombinant progeny/ Total # of progeny X 100% • The map distance gives us info on the distance between genes. It tells us the proportions of recombinant & non-recombinant gametes produced.

Answer 13

``` The expected frequency of multiple exchanges between two genes can be predicted from the distance between them # of observed D.C.O (double cross-over) / # of expected D.C.O ```

Answer 14

Interference= 1- coefficient of coincidence I = 1-.62= 0.38 Interference – tells the percentage of double cross over progeny expected that will not be observed due to the interference in crossing over. -positive if fewer double-crossovers than expected -negative if more double-crossovers than expected Double crossover are the smallest numbers in the progeny

Answer 15

Two strands (of nucleotides) are twisted together around a common axis to form a spiral called a double helix

Answer 16

The two strands are antiparallel. One runs in the 5’ (free phosphate) to 3’ direction (free sugar) and the other 3’ (free sugar) to 5’ (free phosphate) direction.

Answer 17

The helix is right-handed in a clockwise direction giving 10 bases & 3.4 nm per complete turn of the helix. As it spirals away from you, the helix turns in a clockwise direction

Answer 18

a. Hydrogen bonding between complementary bases. A bonded to T by 2 hydrogen bonds, C bonded to G by 3 hydrogen bonds

Answer 19

They are 1. Semi-conservative 2. Conservative 3. Dispersive

Answer 20

a. Leading Strand – new stranded that is synthesized in the 5’ -----> 3’direction, which grows continuously during DNA replication, left to right unwinding DNA can only be synthesized in the 5’ to 3’ direction. b. Lagging strand- is the DNA strand, which grows discontinuously by forming short segments known as Okazaki fragments. It's synthesized in the 5’ ----> 3’direction, opposite right to left unwinding

Answer 21

It's a type of DNA replication, where replication is moving along in both directions from the starting point. This creates 2 replication forks, moving in opposite directions. When the 2 replication forks move to opposite directions, DNA can get ready to replicate DNA quickly (to make complementary DNA strand)

Answer 22

Wildtype alleles is a term used to refer to most common allele in the population, which is displayed as (+) Mutant allele is a rare allele (less than 1% of pop.), which usually result from a mutation.

Answer 23

a. Forward – changes wild type allele to a mutant allele. For example, e+ ---> e b. Reverse – changes a mutant allele back to a wild type. For example, e --> e+ (more rare)

Answer 24

It's a change in the single base pair in DNA. | There are 2 types of base substitutions: transition and transversion

Answer 25

1) Transition: - pyrimidine replaces a pyrimidine (T ----> C) or - purine replaces a purine (A --> G) 2) Transversion (rare): - purine / a pyrimidine are interchanged T ---> A or G, C ----> G or A, A -----> T or C, G ----> C or T

Answer 26

adding or removal of a base pair in the DNA

Answer 27

Translocation means that a piece of chromosome move from one chromosome to another Conservative --> Cut and paste Replicative ---> Copy and paste

Answer 28

Mutagens are natural or artificial environmental agents that cause mutation and increase the rate of mutation Carcinogen - any substance that causes cancer. Mutagens cause changes in the genetic information of an organism, which may sometimes cause cancers. Carcinogens cause cancers through formation of tumors.

Answer 29

The 'Central Dogma' (gene expression) is the process by which the instructions in DNA are converted into a functional product, such as a protein.

Answer 30

The sugar in RNA is ribose. The sugar in DNA is deoxyribose. The nitrogenous bases used in DNA are: Adenine, Guanine, Cytosine, and Thymine. The nitrogenous bases used in RNA are: Adenine, Guanine, Cytosine, and Uracil.

Answer 31

In eukaryotes: initial transcript destined for translation is called pre-mRNA processing -----> processing occurs in nucleus

Answer 32

mRNA processing includes: RNA splicing, the addition of a modified (methylated) nucleotide 5' cap to the 5' end, and the addition of a poly-A tail to the 3' end.

Answer 33

it's the repeating sequence of Adenine (A) nucleotides, which is added to the 3' end

Answer 34

Introns (RNA transcript) are removed by splicing (cut) and exons are joined.

Answer 35

They are primary, secondary, tertiary, and quaternary structures of a protein.

Answer 36

The linear chain of amino acids

Answer 37

The regions are stabilized by hydrogen bonds between atoms of the polypeptide backbone; beta pleated sheets & alpha helices

Answer 38

3D shape stabilized by interactions between side chains

Answer 39

The association of two or more polypeptides of a protein

Answer 40

They are silent, missense, nonsense, and frameshift mutations

Answer 41

Silent mutation – doesn’t alter the amino acid sequence, so it stays in the same box of the codon chart. Redundancy (amino acid can be specified by more than 1 codon)

Answer 42

Missense mutation - alter the amino acid sequence, so it goes from one box of the codon chart to another. Base substitution for which codon on transcribed mRNA specifies wrong amino acid. ex sickle cell anemia

Answer 43

Nonsense mutation - codon is changed from the amino acid to a stop codon, which forms the incomplete polypeptide (amino acid chain - nonfunctional protein)

Answer 44

Frameshift mutation means that we insert or delete a single nucleotide, which causes the disruption in the reading frame of mRNA, so that the resulting protein will be shorter. The function of proteins is inhibited.

Answer 45

Chemically defined media are culture media that contain a known chemical composition. Composed of exact amounts of chemically pure inorganic or organic components. o Ex: glucose salt broth, inorganic synthetic broth Complex media are culture media that contain unknown chemical composition. Composed of organic materials that are not chemically pure o Ex: nutrient broth, agar, blood agar

Answer 46

a. Selection – establish conditions in which only the desired mutant will grow. b. Screen – growth condition where both mutant and wild type are able to grow, but we can distinguish them phenotypically. We can look on the bacterial colony for a particular phenotype.

Answer 47

1) Vertical gene transfer – binary fission (divides into 2), going from one generation to the next. 2) Horizontal gene transfer – transfer genes to members of the same generation.

Answer 48

They are transformation, conjugation and transduction

Answer 49

Transformation: cells must be competent (be able to take in DNA fragments) from the environment and incorporate into own DNA

Answer 50

Natural transformation: when bacteria take up DNA fragments spontaneously from their surroundings Artificial: accomplished in the lab by making cells competent (treat cells with calcium or use electroporation)

Answer 51

Conjugation: is the process by which one bacterium transfers genetic material to another through direct contact; requires cell-to-cell contact, must be opposite mating type, involves F plasmid and formation of Hfr (high frequency of recombination for chromosomal genes) cell.

Answer 52

Donor cell carries plasmid (F+) | Recipient cell lacks plasmid (F-)

Answer 53

Transduction: transfer of DNA from host (bacterial) cell to another bacterial cell via bacteriophage (virus).

Answer 54

F plasmid: a conjugative plasmid that carries many genes required for the transfer of DNA. F' plasmids: F plasmid variants + some bacterial genomic DNA Transfer of F+ plasmid from a F+ to F- through a sex pilus results in a newly formed F+ cell. The plasmid then gets integrated into the host chromosome and converts and F+ to Hfr. Excision of the F plasmid can convert Hfr back to F+. Excision of F plasmid plus host DNA results in F'. • Hfr allows recombination for plasmid DNA & main bacterial chromosome. Increases diversity in bacteria. Occurs on conjugation.

Answer 55

Because their chromosomes contain an integrated F plasmid.

Answer 56

Operon (operator) – an area of DNA (upstream) that controls whether or not DNA gets transcribed

Answer 57

Gene regulation is the process of turning genes on and off

Answer 58

Lac operon: an inducible operon (active in induction - beginning the process), which utilizes lactose (sugar) by E.coli. This is an example of gene regulation

Answer 59

Trp operon is the repressible operon (activates repressor protein, inhibiting transcription); responsible for the production of the amino acid tryptophan.

Answer 60

Helical (spiral) → nucleosome "beads on a string" (first level) ----> 30nm fiber (second level) ------> fiber is organized into loops, scaffolds, domains (third level - 300 nm fiber) -----> metaphase chromosome

Answer 61

It's a compound s-re at the end of eukaryotic chromosome, which contain specific repetitive base pair sequences. They shorten each division They protect the ends of the chromosome from being digested (broken down) by preventing the loss of base pairs during replication

Answer 62

It's the protein unit (mixture of DNA and proteins), which are found in the centromere (black dots - kinetochores) to which spindle fibers attach to in the chromosome

Answer 63

Structure in the chromosome that holds 2 sister chromatids together by cohesion proteins, which are part of the centromere. Centromeres also contain kinetochore proteins, which help the attachment of spindle fibers.

Answer 64

a. Euchromatin: less condensed regions = transcriptionally active b. Heterochromatin: more condensed regions= transcriptionally inactive (RNA polymerase can't read them)

Answer 65

(1) Constitutive heterochromatin - regions that are always permanently inactive (for transcription). Usually contains highly repetitive sequences. (2) Facultative heterochromatin - regions that can go between Euchromatin & Heterochromatin This means that heterochromatin can become euchromatin, and vice versa.

Answer 66

it's the highly condensed (inactive) X chromosome, which can be seen in females. Females have only one active sex chromosome, because they have XX, and one of the X's is a barr body (which is inactive). o Number of X Chromosomes – 1 = # of Barr Bodies o Ex: Trisomy XXX would have 2 Barr Bodies (3-1 = 2)

Answer 67

Bacterial (prokaryotic) - short, circular DNA molecules | Eukaryotic chromosome - long, linear DNA molecules

Answer 68

1. RNA Polymerase I- produces rRNA 2. Polymerase II- produces mRNA 3. Polymerase III- produces tRNA

Answer 69

Basal transcription factors produce low levels of transcription. It requires 3 factors: 1) RNA polymerase II enzyme to make mRNA 2) 5 different proteins called general transcription factors (GTFs) act as a protein helper, which bind to promoter 3) A protein complex called mediator - to switch between transcription initiation and elongation.

Answer 70

Transcription factors are proteins (activators, enhancer, promoter, mediators) that interact directly through DNA binding

Answer 71

Transcriptional activators (transcription factors) are proteins that bind to DNA and stimulate transcription of nearby genes (turn genes on)

Answer 72

A repressor is a protein, which is produced by the regulatory gene and binds to the DNA, inhibiting the expression of one or more genes (turn off transcription).

Answer 73

a group of proteins bind to the DNA (in the chromatin) and change the structure of the chromatin (to expose the promoter). Promoters of inactive genes are hidden in nucleosomes. To activate a gene, transcription factors (proteins) bind to enhancers (DNA sequence) and attract chromatin remodeling proteins. The chromatin remodeling proteins: 1. change the location of nucleosomes 2. remove histones from the DNA; 3. replace core histones with variants (coactivators). As a result, the promoter (the sequence of DNA) becomes more accessible, so that RNA polymerase II can bind to the promoter and transcription can occur.

Answer 74

Prokaryotes: no nucleus, no nucleosomes | But Eukaryotes have nucleus and nucleosomes

Answer 75

the expression of a gene, which depends on whether it is inherited from the male or the female parent. This means that one allele was epigenetically silenced - meaning turned off. Maternally expressed (paternally imprinted ---> paternal gene silenced) ---> suppress growth. Paternally expressed (maternally imprinted ----> maternal gene silenced) ----> enhance growth.

Answer 76

Tumor Suppressor genes are genes whose products block cell cycle progression at checkpoints and stop progression of non-functional cells (Negative regulation). Tumor Suppressor gene prevent cancer under normal conditions, stopping the progression of checkpoints followed by DNA repair or apoptosis.

Answer 77

Oncogenes have the potential to cause cancer | They are mutated forms. They are the altered gene, whose product can act to help make a cell cancerous.

Answer 78

cancer risk increase with age because with every replication of cells (cell division) we lose telomeres, so there is a chance for mutation. As we age, we are exposed to more mutagens (hazardous environments), which eventually can lead to cancer.

Answer 79

We have maternal Inheritance of mitochondria in humans. 1. Develop from the original small amount of mtDNA in the original egg cell 2. inherited through the mother only (maternal inheritance), not the father. This means that the mitochondrial DNA is passed only from mother to offspring. 3. Because of this they provide a way to trace ancestry through an unbroken chain of female ancestors.

Answer 80

Endosymbiotic theory states that mitochondria and chloroplasts are descended from bacteria (prokaryotic cells) that fused with nucleated cells (any cell with a nucleus).

Answer 81

p + q = 1 p = frequency (A) q = frequency (a) p^2 + 2pq+ q^2 = 1 So then… p^2 = AA 2pq= Aa q^2 = aa

Answer 82

PCR multiplies specific segments of DNA

Answer 83

Restriction enzymes splice (cut) the plasmid (circle)

Answer 84

Gel electrophoresis is a method for separation mostly DNA, rarely RNA and protein based on size and charge.

Answer 85

Ligation is the binding gene of interest (specific gene) to the plasmid, so that it can be transformed to the living cells (bacteria).

Answer 86

Transformation is the process of incorporating DNA segment into the chromosome (from the plasmid)

Answer 87

The abnormalities of aneuploidy occur due to non-disjunction in Meiosis. Nondisjunction – chromosome number abnormalities

Answer 88

Occurs in Meiosis, which allows for new combination as compared to the parent. This happens through crossing over and independent assortment

Answer 89

It's an enzyme made up of protein and RNA, which allows for replication at the end of chromosomes. We find this in fetal germ and cancer cells

Answer 90

Spontaneous mutations happen naturally and randomly, which are linked to normal biological or chemical processes in the organism.

Answer 91

Induced (activated) mutations result from the influence of an outside factor, either natural or artificial. For example, natural like UV light or sunlight, which can cause mutation and artificial, such as chemicals in the lab, which also cause mutation.

Answer 92

Proofreading – looking for the mistakes by DNA polymerase, which is able to recognize and correct errors that occur during replication. Exonuclease activity functions in proofreading.

Answer 93

Mismatch repair – fix errors that remain after proofreading.

Answer 94

Excision repair: base excision repair and nucleotide excision repair.

Answer 95

A modified base is removed from DNA strand by base excision repair

Answer 96

Epistasis is a circumstance where the expression of one gene is modified (e.g., masked, inhibited or suppressed) by the expression of one or more other genes. o Gene that is doing the masking o Ex: blood typing, Labrador retrievers

Answer 97

Neither trait is dominant, an intermediate phenotype exists that is a blending ex. flowers in snapdragons

Answer 98

Codominance phenotypic detection of both gene products | ex. Lentils (spotted or dotted)

Answer 99

Complete dominance: Hybrid resembles one of the two parents Incomplete dominance: Hybrid resembles neither parent, blending Codominance: Hybrid shows traits from both parents

Answer 100

It's the hollow that appears in a cell's surface when the cell undergoes cytokines (cytoplasm division) in the process of cell division.

Answer 101

Covalently linked together by phosphodiester bonds. This means that nucleotides are bonded together by phosphodiester bonds, which are covalent (non-metal groups). – A phosphate connects the 5’ carbon of one nucleotide to the 3’ carbon of another

Answer 102

``` Recessive Autosomal Allele o Sickle-cell anemia o Cystic Fibrosis o Tay-Sachs • Dominant Autosomal Allele o Huntington disease ```

Answer 103

- The number of alleles within a population can be greater than two. o Can only have 2 alleles per locus because we have only a pair of chromosomes. o Multiple alleles arise via spontaneous mutations.

Answer 104

when 2 different genes work together to contribute to one single trait.

Answer 105

o Temperature - Can play a role in an organism’s fur color, as well as survivability. 1) Warm temp -----> no melanin ----> light fur 2) Cooler temp -----> melanin -----> dark fur

Answer 106

- It's the phenotype arising from an environment agent (such as radiation) that mimics the effect of a mutant gene. - Ex: PKU disease, missing an enzyme ----> brain damage

Answer 107

Epigenetics is the study of how the factors (such as environment, inheritance) can cause changes that affect the way your genes work. When our genes are affected (activated or deactivated) it will change the gene expression without changing the DNA sequence (no mutation). You have a change in the phenotype through the activation or repression of the gene without changing the gene sequence.

Answer 108

a threadlike condensed s-re made of protein (histones) and a single DNA molecule that carry the genetic information from cell to cell

Answer 109

Trisomy – gain a single chromosome (2n+1) 3 copies of one chromosome are present o Klinefelter’s ---> XXY o Down syndrome

Answer 110

Meiotic recombination serves as accurate chromosome segregation, which requires crossovers Mitotic recombination - repair of DNA damage, which typically generates non-crossovers

Answer 111

Major & minor grooves that are located outside of the helix for allowing proteins to bind to and recognize DNA sequences from outside of the helix.

Answer 112

Nucleic acids, which are the building blocks of DNA or RNA

Answer 113

Nucleotides consist of 1) A nitrogenous base: Adenine, thymine, cytosine, guanine (DNA) & uracil (in RNA) 2) 5- Carbon (Pentose) sugar- ribose (RNA), or deoxyribose (DNA). NOTE: We lack Oxygen in the s-re of DNA 3) Phosphate group

Answer 114

• Transcription (occurs in nucleus) o Step 1: Initiation: RNA polymerase binds to promoter of DNA o Step 2: Elongation: RNA polymerase moves along the template DNA, linking RNA nucleotides together, forming a complementary mRNA molecule (but RNA uses U instead of T) o Step 3: When RNA polymerase reaches termination sequence, it stops o Step 4: RNA is removed from DNA template strand o Step 5: mRNA molecule is released o Step 6: Separated DNA strand forms back into double helix o Step 7: mRNA is further processed before leaving nucleus to become mature (5’ meytlated cap, 3’ poly tail, RNA splicing)

Answer 115

Translation (occurs in cytoplasm) o Step 1: AUG (start codon) encodes for methionine (1st amino acid) o Step 2: 2nd amino acid is in position and an enzyme forms a peptide bond between the two amino acids o Step 3: tRNA for first amino acid is released o Step 4: Ribosome moves to next codon and repeats, adding 3rd amino acid to chain o Step 5: Protein synthesis continues until ribosome reaches a stop codon (UAA, UAG, and UGA) o Step 6: Ribosome detaches from mRNA o Step 7: Amino acid chain (polypeptide) released, folds into a 3D structure

Answer 116

Types of RNA o Ribosomal rRNA – structural component of ribosomes for protein synthesis (mRNA translation) o Messenger mRNA – template for protein synthesis, carries genetic info (mRNA strand) from DNA to the ribosome. o Transfer tRNA – carries amino acids to ribosome for protein synthesis, so that each amino acid corresponds the specific codon of mRNA

Answer 117

1) 5’ methylated cap (methyl group CH3 is added to Guanine) 2) 3’ Poly- A tail (Polyadenylation - adding A nucleotides) 3) RNA splicing (introns are removed by splicing and exons are joined)

Answer 118

mRNA contains codons, which correspond to a particular amino acid. We can have the same amino acid for several codons (redundancy). Uracil replaces Thymine in mRNA

Answer 119

- Only works if you have 2 alleles! • Purpose is to correlate allele & genotype frequency. • Useful in estimating population changes through a few generations. • Not useful for predicting long-term changes but does provide a foundation for modeling.

Answer 120

- Donor cell – organism gives up its entire DNA. | - Recipient cell – receives portion of donor cell’s DNA and incorporates into its own DNA.

Answer 121

An enzyme called telomerase (made of protein and RNA) fix the telomere by adding base pairs, so that telomere sequences will not disappear. The RNA is complementary to the DNA in that repeat telomeric region. This allows for these sections (telomeres) to not be shorter each time.

Answer 122

Genetic material of the mitochondria is referred to as mtDNA. The mitochondrial proteins are encoded by genes in the nucleus. The proteins are made in the cytoplasm, then transported into the mitochondria. MtDNA is developed only in the egg cell ---> maternal inheritance. Genetic material of the chloroplast is referred to as cpDNA. They have compact gene arrangement (includes introns and exons), contains more genes than the mitochondria. Many chloroplasts’ proteins are also encoded by genes in the nucleus.

Answer 123

1. They have their own DNA 2. Like in bacteria, mtDNA (mitochondrial DNA) and cpDNA (chloroplast DNA) are not arranged into _nucleosomes_ 5. Comparisons of rRNA gene sequences suggest mitochondrial and chloroplast genomes derive from a common ancestor of nonsulfur and cyanobacteria (types of ancient bacteria – prokaryotic cell)

Answer 124

a) After DNA polymerase 1 has removed and replaced the primer, a nick remains in the sugar-phosphate linkage. b) DNA ligase seals the nick in the sugar by catalyzing the formation of phosphodiester bond without adding another nucelotide

Answer 125

DNA replication errors, Tautomeric Shifts, Depurination & Deamination, Oxidative Damages, Replication Slippage

Answer 126

If DNA repair occur before replication, we can fix it. If DNA repair doesn’t occur before replication, we get a spontaneous mutation DNA polymerase in rare cases may incorporate a non-complementary base (instead of A-T, it can be G-T), which can lead to the mutation. Exonuclease activity checks the mistakes from 5’ to 3’ by DNA polymerase 1 before replication. Exonuclease is the ability to remove nucleotides one at a time from the end of a chain, fixing it. Exonuclease activity functions in proofreading.

Answer 127

Tautomeric shift is the spontaneous mutation, when N base attaches to another chemical element. For example, Thymine and Guanine - a spontaneous proton shift, when H moves from N to O (keto to enol) Cytosine and Adenine - H moves from one N to another N. (amino to imino) As a result, the molecular formula doesn’t change: the keto and enol forms are tautomers of each other, as well as amino and imino. This change can occur during the DNA replication.

Answer 128

Depurination is the loss of a purine base from a nucleotide. When we lose the bond between the sugar and nitrogenous base, the base pair, such as Guanine (G) will release and instead we get the apurinic site. Deamination is the loss of an amino group (NH2) from a nitrogenous base. For example, when Cytosine loses NH2, it will become Uracil. So, we get a sequence C-G --> U-A --> T-A (mutant sequence), which is easier for DNA to detect, because of Uracil base pair. But, this can be sometimes recognized and repaired because of the change to uracil, so that we add NH2 back (easy process).

Answer 129

Normal byproducts of cellular respiration. The reactive oxygen species: free radicals (such as superoxide, hydroxide, and hydrogen peroxide). It often occurs to Guanine (G), forming mispairing with A, which cause T to A mutant sequence. (G-C ---> GO-C ----> T-A)

Answer 130

During replication slippage, one strand loops out, so that it alters (changes) the newly laid strand causing either trinucleotide repeat expansion or contraction. Trinucleotide repeats are hotspots for mutation.

Answer 131

Base Analogs, Alkylating Agents, Intercalating Agents, Ultraviolet Light, Ionizing Radiation

Answer 132

Base analogs are chemicals with structures similar to our 4 standard base pairs, so that DNA polymerase can’t recognize the difference between them. When our base analog 5-Bromouracil (5 BU) is incorporated during DNA replication, we get the mutation. 5 BU: one tautomer resembling T pairs with A, other tautomer resembling C pairs with G, so that we get T:A ----> C:G substitution.

Answer 133

Alkylating agents are chemicals that add an alkyl group, such as methyl (CH3) or ethyl (CH3-CH2) to nitrogenous bases, which change the base pairing. For example, Ethylmethylsulfonate (Mustard gas) adds an ethyl group to the Guanine (G), so that we get 6-Ethylguanine, which pairs with Thymine (T) instead of Cytosine (C). Here, we get G:C ----> A:T substitution.

Answer 134

Intercalating (additive) agents interfere with DNA replication process. They are acridine dyes, which cause insertions and deletions between purines and pyrimidines leading to frameshift mutations. For example, Proflavin, acridine orange and ethidium bromide – the acridine dyes.

Answer 135

Purines and pyrimidines readily accept UV light, which results in formation of covalent bonds forming between bases molecules on the same DNA strand. For example, when 2 Thymine on the same strand get exposed to UV light, we get Thymine dimers (means the same), which distort the DNA, blocking replication and cell division. UV light works to kill bacteria and can cause skin cancer.

Answer 136

Ionizing radiations – radiations, which have short wavelengths and high energy. For example, X-rays is ionizing radiation. The radiation breaks covalent bonds between sugar-phosphate backbones, which leads to a lot of chromosomal mutations. High doses of radiation kill cells, while lower doses produce point mutations.

Answer 137

1) Non-homologous end-joining happens, when the break ends are directly ligated (come together) without the need for a homologous template, so that it repairs itself without the help of sister chromatids. This is messy (mutagenic), removing some base pairs and ligating (bonding) the 2 strands back together. As a result, we often get some base pairs that end up being deleted there, which were removed. 2) Homologous recombinant repair uses the DNA strands either from homologous chromosomes (DNA is not replicated) or sister chromatid (if DNA has been replicated) to repair a lesion on the other sister chromatid.