PAC548 Genetics Exam

__________ bonds link the 3’ and 5’ hydroxyl groups of DNA

Phosphodiester

__________ and __________ are DNA purines

Adenine; Guanine

__________ and __________ are DNA pyrimidines

Thymine; Cytosine

DNA helixes are coiled __________ around each other

Clockwise

There are __________ per complete helical turn of DNA

10 nucleotides

__________ bonds hold purines and pyrimidines together

Hydrogen

__________ states that the ratio of A to T and C to G is 1:!

Chargaff’s Rule

Typically, each protein-coding gene has two copies in a human diploid genome. What are the 3 exceptions to this rule?

-Alpha-globulin genes

-Ubiquitin genes

-Histone genes

*All have more genes that code for them

__________ make up the major of DNA and are non-coding and repetitive

Introns

True or False: Repetitive DNA can be in tandem repeats or be interspersed

True; introns are back to back

Tandem repeats (introns) are often called __________ DNA

Satellite

What are the 3 sizes of “satellite” DNA?

-Microsatellites (<1 kb)

-Minisatellites (1-30 kb)

-Macrosatellites (>30 kb)

What is the significance of short tandem repeats?

They can be used for forensic identification of individuals, especially as the repeats on each chromosome differ between each person

__________ helps unwind DNA and separates the strands during replication

DNA helicase

__________ relaxes the supercoiling that happens during unwinding of replication

Topoisomerase

__________ keep DNA strands separated during replication

Single stranded binding proteins

During replication, free nucleotides are brought in by __________ to be hydrogen-bonded to the template strand

DNA polymerase

DNA polymerase only moves from __________ to __________

5’; 3’

__________ forms short RNA sequences on the DNA (primers) during replication so that DNA polymerase knows where to attach

Primase

__________ adds in free nucleotides to bridge gaps between Okazaki fragments

DNA ligase

__________ and __________ are RNA pyrimidines

Uracil; Cytosine

RNA is single stranded, __________, and has __________ polarity

Haploid; Positive

Ribosomal RNAs are synthesized directly on DNA templates in the __________

Nucleolus

Transfer RNAs bind to __________ which are translated into proteins by ribosomes

Messenger RNAs

Due to relaxed base-pairing, some tRNAs can bind to more than one mRNA codon. This is referred to as __________ at the third base position of codons

“Wobble” positioning

During transcription, mRNA is read from __________ to __________

3’; 5’

What molecule reads mRNA and binds to the promoter sequence to start transcription?

RNA polymerase II

mRNA is synthesized during transcription from __________ to __________

5’; 3’

During transcriptional splicing, __________ are removed as they will not code for protein

Introns

Introns are spliced by __________

Endonucleases

At the end of transcription, a 5’ __________ is added to protect mRNA

Methyl-guanylate cap

At the end of transcription, a 3’ __________ is added to protect mRNA

Poly-A tail

After transcription, mRNA diffuses to the __________ and DNA strands reassociate using __________

Cytoplasm; Ligase

There are a total of __________ possible mRNA codons

64

__________ is always the translation start codon

AUG; methionine

What are the 3 stop codons?

-UAA

-UGA

-UAG

During translation, the ribosome moves along mRNA from __________ to __________

5’; 3’

During translation, amino acids are added to the __________ end

3’

Proteins are modified mostly in the __________

Goldi apparatus

What are the 8 types of post-translational modifications?

-Adding disulfide bonds

-Hydroxylation

-Glycosylation

-Proteolytic cleavage

-Phosphorylation

-Acetylation

-Methylation

-Ubiquitination

Adding disulfide bonds to a protein causes…

It to change shape

What is the purpose of post-translational modifications?

To give proteins their three-dimensional structure/tertiary structure

Promoter regions before each gene help bind __________ to the DNA template strand, causing transcription to start

RNA polymerase

A 5’-TATAAA-3’ consensus sequence, called the __________, binds transcription factors

TATA box

The TATA box can bind mRNA transcription __________ or __________

Activators; Repressors

What are the 2 possible consequences of mutations in gene regulatory sequences (such as promoters)?

-No gene produced

-Ectopic gene expression

__________ refers to changes in gene function that occur without changing the actual sequence

Epigenetics

How does methylation impact genes?

Methylation turns genes off

Housekeeping genes are always active, so they are __________

Unmethylated

Tetrogens result in __________ if there is significant exposure

Congenital anomalies

__________ wavelengths induce more mutations; these consist of __________ and __________

Shorter; X-rays; Gamma

__________ are longer wavelengths that can still induce mutations

UV rays

Chemical mutagens affect DNA reassembly, replication, and structure by causing __________

Oxidative stress

What are some examples of dsDNA viruses that integrate into the human genome and are highly mutagenic? (7)

-HPV

-EBV

-HepB

-HepC

-HIV

-HTLV

-HHV8

Point mutations involve a __________

Base substitution

A point mutation __________ involves substituting a purine for another purine or a pyrimidine for another pyrimidine

Transition

A point mutation __________ involves substituting a purine for a pyrimidine or a pyrimidine for a purine

Transversion

__________ point mutations occur if a different amino acid is placed

Missense

__________ point mutations occur if a stop codon is placed, creating a truncated protein

Nonsense

True or False: Most point mutations are spontaneous

True

__________ and __________ can increase the frequency of point mutations

Mutagenic Chemicals; UV light

UV light causes __________ where pyrimidine bases become linked

Pyrimidine dimers

Frame shift mutations consist of what 5 types of mutations?

-Deletions

-Insertions

-Duplications

-Trinucleotide repeat amplifications

-Gene conversions

__________ arise from chromosomal breakage during meiosis or from unequal crossing over

Deletions

Single-gene disorders can arise if too many __________ amplifications occur

Trinucleotide repeat

True or False: Families with trinucleotide repeat amplification mutations all have the same disease severity

False; they have different disease severity due to varying repeat lengths

__________ refers to a genetic disorder becoming more severe in successive generations of a family and/or appearing earlier in life

Genetic anticipation

What are 3 common examples of disorders caused by trinucleotide repeat amplifications?

-Myotonic dystrophy

-Huntington’s disease

-Fragile X syndrome

__________ includes one copy of a gene (an allele) being converted into another one during the repair of a DNA mismatch. This causes the daughter cell to lack one of the original 4 alleles (3:1 ratio instead of 2:2)

Gene conversion

__________ mutations usually result in dominant inheritance where the next generation will also have a mutation

Gain of function

__________ mutations are mutations in a protein that is an integral part of a multi-subunit protein complex. This prevents the whole complex from functioning

Dominant-negative

What is an example of a dominant negative mutation disease?

Marfan Syndrome —> FBN1 gene that encodes fibrillin

Nucleotide excision repair corrects __________ caused by UV radiation

Thymine dimers

Mutations in genes that control nucleotide excision repair pathways lead to increased risk of __________

Premature skin cancers

__________ refers to the double-stranded break repair in which an unbroken strand on another chromosome is used as a template to make a sequence for the broken part

Homologous recombination

True or False: Homologous recombination typically leads to mutations

False—> genes go back to normal

__________ refers to the double-stranded break repair in which to ends of a chromosome are joined together

Non-homologous

Is non-homologous or homologous recombination more accurate?

Homologous—> in non-homologous, some nucleotides can be added or lost leading to mutations

What is the treatment for radiation sickness?

Potassium Iodide pills —> binds thyroid tissue and acts as a shield against radioactive iodine

Chromosomes are composed of histones with __________ basepairs of DNA wrapped around the protein 1.75 times

150

Elementary fibers are formed of nucleosomes with __________ histones

8

Elementary fibers coil to make __________

Chromatin fibers

Chromatids can have either __________ or __________

Euchromatin; Heterochromatin

__________ refers to chromatin that has acetylated histones which allow access of transcription machinery to DNA. These genes are active

Euchromatin

__________ refers to chromatin that has methylated histones associated with transcriptional repression. The DNA is inaccessible by transcription machinery, so the genes are inactive

Heterochromatin

Removal of __________ can allow for genes to be turned on. This is a part of epigenetics

Histone proteins

__________ refers to the methylation of an entire X-chromosome

X-inactivation

__________ refers to methylation of genes in one parental chromosome

Imprinting

DNA __________ turns off certain genes

Methylation

__________ are small RNA sequences (around 20 nucleotides long) that are not translated and have multiple targets

MicroRNA (miRNA)

miRNA bind to regular __________ to inhibit its translation or degrade that particular sequence

mRNA—> bind at complementary sequence

__________ are similar to miRNA in that they result in turning off of a gene by degrading an mRNA sequence, however they have very specific targets

Small interfering RNAs (siRNA)

__________ regulates gene expression by silencing specific mRNA molecules, preventing them from being translated into proteins

RNA Interference (RNAi)

Many human diseases, including cancer, have an __________ etiology. As such, we can use therapies that alter __________ patterns on DNA and chromosomes

Epigenetic; Methylation

What is the easiest and most specific epigenetic treatment to create?

RNAi; we can turn off genes that lead to disease

*First was Onpattro in 2018

Each chromosome is a pair of __________ joined together at the centromere

Sister chromatids

Long arms of chromosomes are lettered __________

q

Short arms of chromosomes are lettered __________

p

__________ refers to chromosomes with a centromere in the middle

Metacentric

__________ refers to a chromosome with a centromere close to one end

Acrocentric