ch. 5 genetics Flashcards

Question

nondisjunction

Answer 1

when one or more chromosome pairs or chromatids fail to separate during mitosis. this commonly occurs during anaphase of mitosis, when two chromatids of a single chromosome fail to separate, or during anaphase of meiosis.

Answer 2

a phenomenon that occurs in cells that undergo nondisjunction in mitosis during embryonic development; fraction of body cells have extra or missing chromosomes

Answer 3

when all chromosomes undergo meiotic nondisjunction and produce gametes with twice the number of chromosomes a. is common in plants

Answer 4

a single nucleotide change causing either substitution, insertion, or deletion - the latter two can cause a frameshift mutation **transition mutation** - conversion of a purine to purine/pyrimidine to pyrimidine **transversion mutation** - conversion of a purine to pyrimidine or vice versa

Answer 5

a genome with extra or missing chromosomes, often caused by nondisjunction i. Down syndrome, or **trisomy 21** ii. turner syndrome is a genetic condition in which a female is either completely missing, or partly missing an X chromosome, leading to the genotype XO. iii. Klinefelter's syndrome - male is born with an extra X chromosome

Answer 6

chromosome segments are changed

Answer 7

chromosome segments are repeated on the same chromosome, which can occur from unequal crossing over

Answer 8

chromosome segments are rearranged in reverse orientation

Answer 9

one segment of a chromosome is moved to another chromosome a) can be reciprocal ( two non-homologous chromosomes swap segments) or Robertsonian (one chromosome from a homologous pair becomes attached to another chromosome from a different pair) ex) an extra 21 chromosome attached to chromosome 14 can cause Down syndrome as well, due to the tripled 21 chromosome segment

Answer 10

spontaneous or induced breakage of a chromosomal segment via mutagenic agents or X-rays

Answer 11

include cosmic rays, X-rays, UV rays, radioactivity, chemical compounds including colchicine and mustard gas that can cause genetic mutations. generally also carcinogenic i. colchicine functions by inhibiting spindle formation, which can cause polyploidy

Answer 12

autosomal recessive condition the inability to produce the proper enzyme for phenylalanine breakdown, causing degradation product phenylpyruvic acid to accumulate

Answer 13

autosomal recessive condition fluid buildup in respiratory tracts

Answer 14

autosomal recessive condition lysosome defect in which cells can't breakdown lipids for normal brain function

Answer 15

autosomal dominant condition nervous system degeneration

Answer 16

autosomal dominant condition causes dwarfism

Answer 17

autosomal dominant condition excess cholesterol in blood that progresses into heart disease

Answer 18

sex-linked recessive condition causing abnormal blood clotting

Answer 19

sex-linked recessive condition primarily observed in males

Answer 20

sex-linked recessive condition progressive loss of muscle

Answer 21

trisomy 21

Answer 22

deletion of X chromosome --> XO genotype

Answer 23

extra X chromosome --> XXY genotype

Answer 24

deletion on chromosome 5

Answer 25

amniocentesis or chorionic villus sampling (CVS)

Answer 26

extranuclear genes (genes present in organelles other than the nucleus) are found in mitochondria and chloroplasts i. defects in mitochondrial DNA can reduce a cell's ATP production, and because mitochondrial DNA is inherited only from the mother, all related mitochondrial defects/diseases are also inherited

Answer 27

homozygous - two copies of the same allele are inherited heterozygous - different alleles of the same gene are inherited hemizygous - one single copy of a gene is inherited instead of two (ex: males)

Answer 28

if the recessive is lethal, for example, don't include it in the ratio of genotypes if a phenotype skips generations, be suspicious of an autosomal recessive disorder. if no skip, it is most likely an autosomal dominant disorder. be suspicious for X-linked recessive if a father doesn't have the phenotypes and none of his daughters display it

Answer 29

5' to 3' phosphodiester bonds to form a sugar-phosphate backbone

Answer 30

1. a second chromatid containing a copy of DNA is assembled during interphase -DNA is replicated via semiconservative replication, where one strand is always old and one strand is always new 2. **helicase** unwinds the DNA, forming a replication fork - single stranded binding proteins attach to each strand of uncoiled DNA to keep them separate - topoisomerases break and rejoin the DNA double helix, preventing knots 3. **DNA polymerase** moves from the 3' to 5' direction only, and synthesizes a new strand that is antiparallel (5' to 3') - the DNA polymerase has to go back to the replication fork and work away from it, producing Okazaki fragments - DNA ligase connects these fragments 4. Primase creates a small strip of RNA - DNA polymerase I replaces base pairs form the RNA primers and functions in DNA repair - DNA polymerase III is mainly for replication 5. Ligase glues two strands of DNA together

Answer 31

UAA, UAG, and UGA which do not code for any amino acids

Answer 32

a clover shaped transporter of anticodons one end attaches to the amino acid being transported, and the other end is the anticodon which base pairs with the codon in mRNA **Wobbles**: the exact base pair of the third nucleotide in the codon is often not required, allowing 45 different tRNA's to base-pair with 61 codons that code for amino acids the clover shape is held together by hydrogen bonds smallest RNA molecule

Answer 33

form ribosomes * a ribosome has four total binding sites - one for mRNA - three for tRNA P site: carries the growing polypeptide chain A site: 2nd tRNA that delivers the next amino acid E site: for the empty tRNA before leaving the ribosome *note*: the ribosome is assembled in nucleolus but the large and small subunits are exported separately to the cytoplasm

Answer 34

1. **initiation** - RNA polymerase attaches to the promoter region on DNA and unzips the DNA into 2 strands. Promoter region for mRNA transcription often contains TATA 2. **elongation** - RNA polymerase continues unzipping DNA and assembles RNA nucleotides using one strand of DNA as a template. Only one strand is transcribed, from the template = (-) antisense strand, while the other is the coding (+) sense strand for protection against degradation 3. **termination** - occurs when RNA polymerase reaches a special sequence, often AAAAAA in eukaryotes

Answer 35

1. **5' cap (5' G-P-P-P)**: this sequence is added the the 5' end of the ,=mRNA; a guanine with three phosphate groups (GTP) provides stability for mRNA and a point of attachment for ribosomes 2. **A poly-A tail (-A-A-A...A-A-3')**: this sequence is attached to the 3' end of the mRNA. the poly A tail consists of 200 A nucleotides that serve to provide stability and control the movement of mRNA across the nuclear envelope 3. **RNA splicing** : removes nucleotide segments from mRNA before mRNA moves into the cytoplasm via small nuclear ribonucleoproteins (snRNP's). the spliceosome deletes the introns and splices the exons 4. **alternative splicing**: allows different mRNA to be generated from the same RNA transcript by selectively removing differences of an RNA transcript into different combinations

Answer 36

1. **initiation**: the small ribosome subunit attaches to the 5' end of the mRNA; a tRNA methionine attaches to the start sequence of mRNA (AUG), and the large ribosomal subunit attaches to form a compete complex. requires 1 GTP 2. **elongation**: next tRNA binds to the A site, peptide bond formation occurs, and the tRNA without methionine is released. the tRNA currently in the A site moves to the P site (translocation) and the next tRNA comes into the A site to repeat the process. this requires 2 GTP per link 3. **termination**: when the ribosome encounters the stop codon (either UAG, UAA, or UGA), the polypeptide and the two ribosomal subunits all release due to a release factor breaking down the bond between tRNA and the final amino acid of the polypeptide i. while the polypeptide is being translated, amino acid sequences are determining the folding conformation, which is a process that requires assistance from chaperone proteins and 1 GTP 4. **post-translation**: translation begins on a free floating ribosome; a signal peptide at the beginning of the translated polypeptide may direct the ribosome to attach to the ER, in which case the polypeptide is injected into the ER lumen. if injected, the polypeptide may be secreted from the cell via the Golgi apparatus

Answer 37

methionine vs. n-formylmethionine

Answer 38

most amino acids have more than one codon specifying them

Answer 39

when a mutation occurs, but the new codon still codes for the same amino acid, therefore the effect is silenced

Answer 40

the new codon codes for a stop codon

Answer 41

there is no change in protein function

Answer 42

a new codon codes for a new amino acid ---> can have a minor or fatal results (as in sickle cell anemia where glu-->val)

Answer 43

DNA polymerase checks base pairs

Answer 44

enzymes repair the errors DNA polymerase missed - mismatch repair deals with correcting mismatches between normal bases

Answer 45

enzymes remove nucleotides damaged by mutagens

Answer 46

can be used to repair tissues like thymine dimers

Answer 47

similar in function to nucleotide excision repair, but uses different enzymes. the main difference is that nucleotide excision will chunk out an entire segment around the faulty base by nicking the entire surrounding phosphodiester backbone, not just the faulty base base excision repair first chunks out just the faulty base, then the phosphodiester backbone around the base is cut out, then polymerase I does some 5' to 3' exonuclease cutting and fills in the gaps

Answer 48

structure formed when DNA is coiled around bundles of 8-9 histone proteins, kind of like beads on a string during cell division (interphase), however, chromatin exists as two types: 1. **euchromatin**: chromatin is loosely bound to nucleosomes; present when DNA is actively being transcribed 2. **heterochromatin**: areas of tightly packed nucleosomes where DNA is inactive and appears darker. contains satellite DNA

Answer 49

DNA segments that can move to a new location on either the same or different chromosome two types: 1. insertion sequences that consist of only one gene that codes just for the enzyme that transports it (transposase) 2. complex transposons code for extra features: replication, antibiotic resistance

Answer 50

the human genome contains many types of DNA that do not actually code for proteins or RNA, and because most of the genome appears to be repetitive DNA, there are lots of transposable elements present as well **pseudogenes are former genes that have accumulated mutations over a long time and no longer produce a function protein**

Answer 51

~24,000 majority consisting of repetitive DNA

Answer 52

* **nucleic acid** - RNA or DNA that can be double or single stranded * **capsid** - a protein coat that encloses the nucleic acid * **capsomeres** - surrounds capsid of some viruses and incorporates phospholipids and proteins obtained from the cell membrane of the host

Answer 53

a virus that only attacks bacteria, is usually specific to a type of cell via viral surface proteins binding to specific receptors on the host cell of the species

Answer 54

when the virus penetrates the host cell membrane and uses host machinery to produce nucleic acids and viral proteins that are then assembled to make new viruses a) these viruses then burst out of the cell and infect other cells **DNA viruses** - replicate by first replicating DNA and forming new viral DNA, which is then transcribed to produce viral proteins that combine with DNA to form new viruses **RNA virus** - RNA serves as mRNA which is translated into protein. this protein and RNA assemble to form a new RNA virus **retroviruses** - single stranded RNA viruses that use reverse transcriptase to make a DNA complement of their RNA by hijacking the host cell's replicating machinery. this RNA is then used to manufacture mRNA or enter the lysogenic cycle (becoming incorporated into the host DNA) - a common example of a retrovirus is HIV

Answer 55

when viral DNA is incorporated into the DNA of the host cell; there are two phases to this cycle: a) **dormant stage** - the virus is referred to as a provirus and remains inactive until an external stimuli triggers the virus b) when triggered, the virus enters the lytic cycle, and follows the same steps as mentioned in the previous bullet

Answer 56

1. **attachment**: the phage attaches to the surface of the host 2. **penetration**: the viral DNA enters the host cell 3. **biosynthesis**: phage DNA replicates and phage proteins are made 4. **maturation**: new phage particles are assembled 5. **lysis**: the cell lyses, releasing the newly made phages

Answer 57

are not viruses or cells, but are infectious, mis-folded versions of proteins in the brain that cause normal versions of proteins to also become mis-folded. prions are fatal, and are implicated in diseases such as Mad Cow disease, kuru, scrapie in sheep, and Creutzfeldt-Jakob disease

Answer 58

very small circular RNA molecules that infect plants. these do not encode for proteins, but replicate in host plant cells via host enzymes, and cause errors in the regulatory systems of plant growth

Answer 59

bacteria reproduce via this method in which the chromosome replicates, the cell divides into two cells, and each cell now holds the exact same copy of the original chromosome

Answer 60

short, circular DNA outside of chromosomes that carry genes that are beneficial, but not essential for survival have a restriction site, LacZ gene, and ampicillin resistance gene

Answer 61

plasmids that can incorporate bacterial chromosomes what help bacteria gain characteristics like antibiotic resistance

Answer 62

donor bacteria produces a bridge (pilus) and connect to the recipient bacteria; this allows the donor to send a chromosome or plasmid to the recipient, thus allowing recombination to occur a. an F plasmid allows a pilus to form, and once the recipient receives the F plasmid, it is now F+ and can donate this plasmid as well b. pili are also used for cell adhesion

Answer 63

DNA is introduced into a genome via virus. when the virus is assembled during the lytic cycle, some bacterial DNA is incorporated in the place of viral DNA. when the virus infects another host, the bacterial DNA part that it delivers can recombine with the resident DNA

Answer 64

bacteria take in DNA from surroundings and incorporate it into the genome

Answer 65

region of DNA that controls gene transcription and consists of i. **promoter**: sequence of DNA where RNA polymerase attaches to begin transcription ii. **operator**: region that can block action of RNA polymerase if occupied by repressor proteins iii. **structural genes**: DNA sequences that code for related proteins iv. **regulatory genes**: located outside of operon region, and produce repressor proteins. others produce activator proteins that assist the attachment of RNA polymerase to the promoter region

Answer 66

controls the breakdown of lactose; the regulatory gene produces an active repressor that binds to the operator and blocks RNA polymerase i. the lac operon consists of three lac genes (Z,Y,A), which code for the following: a. B-galactosidase that converts lactose --> glucose and galactose b. lactose permease that transports lactose into the cell c. thiogalactoside transacetylase ii. when lactose is available, lactose binds to the repressor and inactivates it, therefore allowing RNA polymerase to transcribe the genes. Moreover, lactose induces the operon, and the enzymes that the operon produces as a result are termed "inducible enzyme"

Answer 67

when glucose is low, cAMP is high. this cAMP binds to a CAP binding site of the promoter, which enhances the binding and transcription via RNA polymerase, allowing for lactose to be broken down if lactose AND glucose are high, the operon is shut off this is because cAMP is low, and doesn't bind to CAP. bacteria uses one sugar at a time, and prefers glucose

Answer 68

produces enzymes for tryptophan synthesis; regulatory genes produce and inactive repressor, which allows RNA polymerase to produce enzymes i. when tryptophan is available, we no longer need to synthesize it internally: it binds to an inactive repressor and activates the repressor, which binds to the operator and blocks polymerase. Tryptophan is a co-repressor here

Answer 69

are when structural genes stop producing enzymes only in the presence of an active repressor. unlike repressive enzymes, some genes are constitutive (constantly expressed) either naturally or due to mutation

Answer 70

repressors and enhancers/activators that influence RNA polymerase attachment to the promoter region. i. utilizing the presence or absence of activators allows for cell type-specific transcription (for example: a liver versus a lens cell transcribe different genes)

Answer 71

involves regulation at the chromosome level i. **methylation histones** - results in tighter packing that prevents transcription ii. **acetylation of histones** - uncoils chromatin, encouraging transcription iii. **direct DNA methylation** - epigenetic control of DNA that can be inherited and usually leads to lower expression

Answer 72

noncoding RNA (ncRNA) plays a role in controlling gene expressions as well. some are even involved in chromatin modification i. **micro RNA (miRNA)** - single stranded RNA molecules that bind to complementary RNA sequences and either degrade the target or block its translation

Answer 73

function similarly to miRNA, aside from a subtle difference between the precursors a. in both cases, double stranded RNA becomes single stranded and *then* carries out its function b. RNA interference (RNAi) is the blocking of gene expression using siRNAs

Answer 74

97% of human DNA does not code for protein product, but rather for non-coding DNA i. non-coding DNA includes regulatory sequences, introns, tandem repeats, and repetitive sequences that are never transcribed ii. tandem repeats are abnormally long stretches of back-to-back repetitive sequences within an affected gene (e.g. Huntington's)