Molecular Genetics Workshop

Question 1

Why is DNA replication semi-conservative?

Answer 1

because half of the original DNA molecule is incorporated into each daughter strand.

Question 2

What are the steps to DNA replication?

Answer 2

1. DNA helix is unwond by helicase where the H bonds are broken.
2. DNA polymerasesynthesizes new strands complimentary to the original parental strands in the 5’ to 3’ direction beginning at the origin of replication.
3. replication fork is formed
4. The leading strand is synthesized continuously using one RNA primer.
5. The lagging strand is synthesized discontinuously using a RNA primer for every Okazaki fragment.

Question 3

What is transcription?

Answer 3

Theprocess by which information stored in the bases of DNA is copied into RNA.

Question 4

What are the steps for transcription?

Answer 4

1. RNA polymerase binds to the TATA box in the promoter region of the DNA template strand.
2. Only one strand of the DNA is used for a given gene.
3. Nucleotides are added in a 5’ to 3’ direction
4. Heterogeneous nuclear RNA (hnRNA) is formed
5. The introns are cleaved out and the exons spliced together to form the mRNA
6. The 5’ end of the mRNA is capped
7. The 3’ poly A tail is added
8. The finished mRNA product leaves the nucleus through nuclear pores.

Question 5

What is translation?

Answer 5

Translation is the synthesis of an amino acid chain using mRNA as a template.

Question 6

What are the steps of translation?

Answer 6

1. Occurs in the cytoplasm and requires energy (GTP)
2. mRNA bind to a ribosome, Translation begins when the ribosome encounters a start codon.
3. tRNA delivers amino acids to the ribosomes.
4. the tRNA/ amino acid complex temporarily binds the mRNA codon.
5. An enzyme (peptidyl transferase) fogers a peptide bond between adjacent amino acids.
6. Pretein synthesis stops when a stop codon is reached.
7. Post-translational modifications occur to the protein product.

Question 7

what are the three main classes of small scale mutations?

Answer 7

1. Base substitution
2. Deletions
3. Insertions

Question 8

Describe base substitution

Answer 8

one base pair is substituted for another.
Transition- substitution of a pyrimidine (C or T) by another pyrimidine, or of a purine(A or G) by another purine.
Transversion- substitution of a pyrimidine by a purine or of a purine by a pyrimidine.

Question 9

Describe deletions

Answer 9

One or more nucleotides are lost from a sequence

Question 10

Describe insertions

Answer 10

One or more nucleotides are added to a sequence.

This can include transposition- a sequence is inserted at an incorrect location in the DNA.

Question 11

What is direct repair

Answer 11

reverses DNA damage without cutting the deoxyribose phosphate backbone

Question 12

what is base excision repair (BER)

Answer 12

used when incorrect bases are present in the DNA. The damaged base is recognized by a glycosylase and is hydrolytically removed from the deoxyribose phosphate backbone. The leaves an apurinic or apyrimidic site where the purine or pyrimidine was removed. The correct base is then inserted and the break is sealed by DNA ligase.

Question 13

what is Mismatch repairs

Answer 13

method similar to BER to remedy correct pairings of the normal bases.

Question 14

what is nucleotide excision repair (NER)

Answer 14

removes thymine dimer and bulky adducts. The are of DNA surrounding and including the damaged portion is unwond and an endonuclease makes cuts on both the 5’ and 3’ side of the damage. The bases are removed by an exonuclease and DNA is resynthesized, using the sister strand as a template to fill the gap. DNA ligase seals the new section into the backbone.

Question 15

what is post-replication repair

Answer 15

used to repair double strand breaks. This involves a type of recombinational repair in which a single strand of DNA from a homologous chromosomes is used to resynthesize the missing portion. Broken ends can also be rejoined directly and ligated together. However, the original sequence is not always maintained and mutations such as translocations can often occur as a result of this.

Question 16

what is a nucleosome

Answer 16

most basic unit. consst of 8 histone proteins. DNA is wound almost two times around this protein core to produce a “bead-like” structure.

Question 17

what are the guidelines for cross-over

Answer 17

• it occurs randomly along the entire chromosome.
• Two genes close together on the chromosome have a low chance of cross-over (the genes are said to be linked).
• The further apart two genes are on a chromosome, the greater the chance of these genes crossing-over.

Question 18

what are the events that occur during recombination?

Answer 18

1. Homologous pair line up.
2. An endonuclease nicks a single strand of DNA on each homolog at the same place.
3. The homologs exchange strands and are ligated together forming the Holliday structure.
4. Branching migration occur,incorporating a portion of the opposite strand into each molecule.
5. Cleavage occurs: if the same strands are cleaved the original chromosomes are reformed. If the opposite strands are cleaved then recombinant chromosomes results.

Question 19

constitutional chromosomal abnormalities

Answer 19

the abnormality is found in all cells of the body.

Question 20

Somatic chromosomal abnormalities

Answer 20

the abnormality if found only in certain cells or tissues.

Question 21

Numerical chromosomal abnormalities

Answer 21

The gain or loss of complete chromosomes

Question 22

Structural chromosomal abnormalities

Answer 22

The formation of abnormal chromosomes through the misrepair of chromosome breaks or a malfunction during recombination

Question 23

Aneuploidy

Answer 23

One or more chromosomes are missing or are present in more than the normal number. Usually results from nondisjunction, which is the failure of paired chromosome to separate in anaphase (usually during meiosis 1)

Question 24

Monosomy

Answer 24

The loss of a single chromosome.
Autosomal monosomy is always lethal.
Monosomy of sex chromosome X results in Turner’s syndrome (45,X)

Question 25

Trisomy

Answer 25

``` The gain of an extra chromosome. Down syndrome (Trisomy 21) ```

Question 26

Tetrasomy

Answer 26

The gain of an extra pair of homologous chromosomes. | Tetrasomy 9p, Tetrasomy 18p

Question 27

Euploidy

Answer 27

An extra, complete set of chromosomes is present or missing.

Question 28

Polyploidy

Answer 28

More than two sets of chromosomesare present. | Triploid, tetraploid, pentaploid.

Question 29

Monoploidy

Answer 29

A complete chromosome set is missing. | Lethal

Question 30

Mixoploidy Mosaicism

Answer 30

Two or more genetically different cell lines within a single individual derived from a single zygote.

Question 31

Mixoploidy Chimerism

Answer 31

Two or more genetically different cell lines withing a single individual derived from different zygotes

Question 32

what are the two main ways that structural abnormalities arise:

Answer 32

recombination malfunction and mispair of chromosome breaks

Question 33

Inversion malfunction

Answer 33

The chromosome segment is rejoined opposite of its normal configuration without loss of genetic information

Question 34

Duplication malfunction

Answer 34

segment of the chromosome is repeated

Question 35

Deletion malfunction

Answer 35

a segment of the chromosome is lost

Question 36

Translocation malfunction

Answer 36

chromosomal materil is exchanged between non-homologous chromosomes.

Question 37

Translocation reciprocal

Answer 37

there is no loss of genetic infoormation although gene arrangement is altered.

Question 38

Translocation Robertsonian

Answer 38

the short arm of two chromosomes breaks off and the long arms are fused together, this can result in a balanced translocation or a unbalanced translocation in which genetic material is gained or lost.

Question 39

Negative control or repression

Answer 39

protein binds to DNA in order to interfere with the binding of the RNA polymerase to the promoter region. This prevents transcription

Question 40

Positive control or activation

Answer 40

A protein binds to DNA in order to facilitate the binding of the RNA polymerase to the promoter region. This initiates transcription.

Question 41

What is a Polymerase Chain Reaction (PCR)?

Answer 41

used to selectively amplify target DNA

Question 42

What are the steps for PCR?

Answer 42

- denaturing (94C) the original DNA strand.; this produces two complimentary single strands of DNA. - Annealing (54C) primers to the single stranded DNA; the specific singl stranded primers that are used attached to the complimentary portion of single stranded DNA,. - DNA polymerase attaches to the prime/DNA complex and moves down the DNA chin reading the template strand and adding the appropiate complimentary base. This externsion (72C) produces a new double stranded DNA molecule from each strand of the original DNA causing an exponenial increase in the number of copies of a particular gene.

Question 43

DNA sequencing

Answer 43

- same as PCR. - run in the presence of small amt of ddNTPs which lack hydroxyl group at the 3' position as well as dNTPs. The addition of one ddNTPs to the growing chain will terminate chain elongation since no further nucleotides can be added without the 3' hydroxyl group.

Question 44

Mitochondrial DNA (mtDNA)

Answer 44

- maternally inherited. - mitochondria from sperm are destroyed by the egg after fertilization leaving only maternal mtDNA originally found in the unfertilized egg.

Question 45

Cystic Firbrosis (CF)

Answer 45

Caused by loss of function mutations in the CFTR gene and it is the most common lethal genetic disease in the US. The normal gene codes for a membrane protein that transport chloride ions in and out of cells. This has the greatest effect on the epithelial cells lining organs and it is particular evident in the lining of the lungs.

Question 46

Huntington disease (HD)

Answer 46

results from a gain of function mutations that produces an autosomal dominant disorder characterized by neurodegeneration. Caused by expansion of a triplet repeat, whcih is a set of three nucleotides (CAG) that code for glutamine.

Question 47

what are proto-oncogenes

Answer 47

non-mutant versions of genes that control cell proliferation.

Question 48

what are oncogenes activated through

Answer 48

Amplification Point mutations Chromosomal translocations Trasnposition

Question 49

Amplification

Answer 49

Hundreds of extra copies of a gene may be present.

Question 50

Point mutations

Answer 50

can lead to excessive cellular response

Question 51

chromosomal translocations

Answer 51

a novel gene is created.

Question 52

transposition

Answer 52

a gene is moved from a relatively inactive area of chromatin to an active area where it is consequently transcribed in abnormal amounts.

Question 53

How can loss of function in a tumor suppressor gene can occut

Answer 53

they can occur through: - Deletion of a portion of chromosome containing the gene. - A point mutation within the DNA sequence of the gene - Methylation of DNA the prevents the tumor suppressor gene from being transcribed.

Question 54

what are the four approaches to gene therapy:

Answer 54

- Inserting a normal gene into the genome to replace a nonfunctional gene. - Replacing a nonfunctional gene through homologus recombination. - Repairing the mutant gene by reversing the original mutation. - Altering the regulation of a gene.