types of mutations and the sources: translation- lecture 3

Question 1

how can just 4 bases encode 20 amino acids

Answer 1

A triplet code would be the smallest set of four bases capable of encoding all 20 amino acids. In other terms, it is a specific set of three consecutive nucleotides that functions as a part of the genetic code and specifies a certain amino acid in a protein or initiates or terminates protein synthesis

you lose the frame if you remove one or two, but if you remove 3 or add 3 the frame is preserved so it works in 3 amino acids

Question 2

the genetic code for rna is made of amino acids, and each triplet is called a

Answer 2

codon (64 codons)
1- there are stop codons
2) there are differing levels of redundancy, ranging from 6 (serine) to 1 (methionine)
-most redundancy found in third position of the codon

Question 3

nirenberg used what for his experiement

Answer 3

poly u

Question 4

transfer rna

Answer 4

a small RNA molecule that plays a key role in protein synthesis. Transfer RNA serves as a link (or adaptor) between the messenger RNA (mRNA) molecule and the growing chain of amino acids that make up a protein

transfer RNA (tRNA), small molecule in cells that carries amino acids to organelles called ribosomes, where they are linked into proteins

structure: molecules are composed of one short chain of RNA, 70-90 nucleotides in length, folded into a trefoil shape

Question 5

how does trna work

Answer 5

Question 6

ribosome

Answer 6

A ribosome is an intercellular structure made of both RNA and protein, and it is the site of protein synthesis in the cell. The ribosome reads the messenger RNA (mRNA) sequence and translates that genetic code into a specified string of amino acids, which grow into long chains that fold to form proteins

Question 7

start codon

Answer 7

aug-methionine

Question 8

initiation of translation in eukaryotes is at the blank prime cap

Answer 8

5’

Question 9

explain how translation works

Answer 9

Question 10

are mrna and amino acids to protein 1 to 1 ratio (as in, you can make multiple proteins from one mrna)

Answer 10

no, you can make multiple protein molecules from the same mrna

Question 11

single nucleotide polymorphism (snips)

Answer 11

A DNA sequence variation that occurs when a single nucleotide (adenine, thymine, cytosine, or guanine) in the genome sequence is altered and the particular alteration is present in at least 1% of the population

Question 12

which mutations are passed on to the next generation and which ones arent

Answer 12

germ cell mutations are passed on to the next generation while somatic cell mutations arent

Question 13

what are somatic cells

Answer 13

somatic cells are any cell of a living organism other than the reproductive cells

mutations occurring in somatic cells arent passed on to the next generation (affect the body in which they occur but dont pass on)

mutations in germline cells (cell that generate gametes) are passed on

Question 14

gamete

Answer 14

a mature male or female germ cell usually possessing a haploid chromosome set and capable of initiating formation of a new diploid individual by fusion with a gamete of the opposite sex

unfertilized reproductive cells (one from each parent, Each of those gametes had 23 chromosomes, so that after the union of those gametes, when you were just a single cell, you had 46 chromosomes. Or, 23 pairs of chromosomes)

Question 15

zygote

Answer 15

fertilized egg cell that results from the union of a female gamete (egg, or ovum) with a male gamete (sperm). In the embryonic development of humans and other animals, the zygote stage is brief and is followed by cleavage, when the single cell becomes subdivided into smaller cells

Question 16

why are somatic mutations bad

Answer 16

they dont contribute to future generations but they can be problematic

cancer is caused by the loss of proper cell cycle regulation and may be caused by the accumulation of mutations affecting a few key genes

Question 17

Somatic & Germline Mutations

Answer 17

Germline mutations are changes to your DNA that you inherit from the egg and sperm cells during conception. Somatic mutations are changes to your DNA that happen after conception to cells other than the egg and sperm

Question 18

A known mutation causing cystic fibrosis

Answer 18

cystic fibrosis, deletion of amino acid phe (need that amino acid to make sure the molecule is stable enough to leave and get translated, so protein is unstable and degrades before reaching membrane)

Question 19

nucleotide substitution that creates a stop codon

Answer 19

nonsense mutation (truncated protein)

Question 20

nucleotide substitution that doesnt change the amino acid

Answer 20

a synonymous mutation, or silent mutation

Question 21

nucleotide substitution that changes the protein

Answer 21

a nonsynonymous mutation, or missense mutation

Question 22

example of nucleotide substitution in public health

Answer 22

Question 23

major type of dna damage

Answer 23

uv light thymine dimers

Cyclobuthane thymine dimer is a photolesion produced by UV radiation in sunlight and is considered as a potential factor causing skin cancer. It is formed as a covalently bonded complex of two adjacent thymines on a single strand of DNA.

UV radiation is limited in its effect in two ways. First,
it cannot pass through our skin, so that it can only cause mutations in cells that are directly exposed to the sun. This is why sun exposure is known to
increase an individual’s risk of developing skin cancer, but not stomach cancer. In addition, UV radiation can cause a very specific type of DNA damage, which is a covalent bond between two adjacent pyrimidine
bases (such as TT, for example). If left unrepaired, this DNA damage can cause errors during DNA replication, leading to changes at the level of one or two base pairs.

Question 24

way to repair dna

Answer 24

Question 25

another major type of dna damage

Answer 25

ionizing radiation

Question 26

third major type of dna damage

Answer 26

chromosomal rearrangements

Question 27

4th major type of dna damage

Answer 27

chemical mutagens like mustard gas

Question 28

chromosomes

Answer 28

a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes Normally, each cell in the human body has 23 pairs of chromosomes (46 total chromosomes). Half come from the mother; the other half come from the father. Two of the chromosomes (the X and the Y chromosome) determine your sex as male or female when you are born.

Question 29

how do we measure mutation

Answer 29

ames test: a biological assay to assess the mutagenic potential of chemical compounds. It utilizes bacteria to test whether a given chemical can cause mutations in the DNA of the test organism

Question 30

purines

Answer 30

larger nucleotides with 2 ring structure, adenine and guanine

Question 31

pyrimidines

Answer 31

smaller nucleotides with only one ring: thymine and cytosine (in rna, cytosine and uracil)

Question 32

depurination

Answer 32

loss of purine a or g component of nucleotides, happens spontaneously and may result in mutation (more common than losing pyrimidines)

Question 33

transposable elements

Answer 33

little pieces of dna in genomes that are capable of moving around/copying themselves in genome

Question 34

At one end of tRNA is the

Answer 34

anti- codon, the three nucleotides that undergo pairing with the corresponding codon in the mRNA

Question 35

an enzyme called () connects specific amino acids to their appropriate tRNA molecule, via a covalent bond. Most organisms have one () for each amino acid.

Answer 35

aminoacyl tRNA synthetase

Question 36

tRNA not bound to an amino acid is an () and one that is bound to an amino acid is a ().

Answer 36

uncharged tRNA charged tRNA

Question 37

During translation initiation in eukaryotes...

Answer 37

initiation factors, a special “initiator” tRNA charged with methionine, and the small subunit of a ribosome all assemble at the 5’ cap of the mRNA. This complex, which is called the initiation complex, scans the mRNA for an AUG start codon, moving along the mRNA from the 5’ towards the 3’ end. When this complex encounters an AUG, the initiator tRNA, which has the anticodon 5’-CAU-3’, can base pair with it. This sets the start site for translation. Note that even though AUG is the first codon to be translated, it is not typically the first codon in the mRNA: there is a preceding region of mRNA that is not translated. Once the initiation complex has established the connection to the AUG codon, the large subunit of the ribosome joins. The polypeptide is synthesized from the amino end to the carboxyl end, meaning that methionine will be the amino acid at the amino end of the polypeptide. Note that the AUG codon is critical for the establishment of the proper reading frame

Question 38

the initial methionine tRNA is located in the

Answer 38

central peptidyl site (P-site)

Question 39

3 sites of ribosome

Answer 39

p site, then a site, then e site (exit, last one)

Question 40

mutations that occur during normal biological processes such as DNA replication or cell division are considered

Answer 40

spontaneous

Question 41

ionizing radiation

Answer 41

In contrast to UV radiation, ionizing radiation can penetrate deeply into tissues, and so causes mutations throughout the body, instead of only in the skin. It can cause DNA damage in a variety of ways, including damaging bases and causing breaks in the sugar-phosphate backbone. Damaged bases can misspair, causing small-scale gene mutations, while double-stranded breaks can fragment chromosomes, causing chromosomal mutations. When the chromosome fragments are put back together, a number of different chromosomal rearrangements can occur. These include small- and large-scale deletions and duplications, inversions, insertions, and translocations that can affect hundreds or even thousands of genes

Question 42

chemical agents

Answer 42

Like those caused by ionizing radiation, mutations caused by chemical agents can affect all cells in the body. This is because chemical agents can circulate in the blood and lymph, so that all cells, including both somatic and germ cells, are exposed. However, unlike ionizing radiation, chemical agents are generally limited to causing smaller-scale gene mutations, because they affect individual bases.

Question 43

alkylating agents

Answer 43

These chemicals add bulky hydrocarbon groups to DNA bases, affecting their ability to base-pair. One type of alkylating agent is mustard gas, which was used during World War I. Exposure to this mutagen causes such severe DNA damage that cells of affected individuals die, causing blistering, bleeding, and other tissue damage. Survivors are also at an increased risk of developing cancer. Alkylating agents are used by scientists to induce mutations in experimental organisms (because, as noted above, it’s possible to derive information about the function of a gene by disrupting that function mutationally). For example, ethylmethylsulfonate (EMS) changes guanine to produce a modified nucleotide which pairs with thymine. Thus, EMS produces C * G → T * A changes

Question 44

Mutations may result from spontaneous chemical changes in DNA. One such change is depurination:

Answer 44

the loss of a purine base [i.e., an A or a G] from a nucleotide. Depurination results when the covalent bond connecting the purine to the deoxyribose sugar breaks, producing an apurinic site, a nucleotide that lacks its purine base. An apurinic site cannot act as a template for a complementary base in replication. In the absence of base-pairing constraints, an incorrect nucleotide (usually adenine) is incorporated into the newly synthesized DNA strand opposite the apurinic site. Pyrimidines are less prone to this kind of spontaneous decay

Question 45

Biological agents such as transposons (transposable elements) can cause mutations. Transposons are

Answer 45

mobile genetic elements that can either copy and paste themselves into new sites in the genome or cut themselves out of their current location and insert into a new one. They were first discovered by Barbara McClintock in her studies of the pigmentation of corn kernels. When transposons insert themselves, they can disrupt the coding or regulatory sequences of genes, which can interfere with their functions. An example of the mutagenic effect of transposable elements is seen in the color of grapes. Black and red grapes result from the production of red pigments, called anthocyanins, which are lacking in white grapes. White grapes resulted from a mutation caused by the insertion of a transposable element into the anthocyanin-producing gene in black grapes that turned off the production of anthocyanins. Red grapes resulted from a second mutation that occurred in white grapes removing most, but not all, of the transposon. This switched anthocyanin production back on, but not as intensely as in the original black grapes. In other cases, transposons insert into noncoding regions and do not cause any phenotypic consequences. Genomes bear testimony to past bouts of transposon activity: around 10% of the human genome consists of copies of a particular element, Alu, which is no longer actively undergoing transposition, but which was clearly highly active in the past.