Biochem 432: Genetics

Question 1

Describe the two types of sequence organization for prokaryotic genes

Answer 1

1. Monocistronic prokaryotic genes encode one protein product in a single RNA transcript.
2. Polycistronic prokaryotic genes encode multiple protein products in a single RNA transcript. Polycistronic genes are not organized at random; their gene products frequently have a related function or are part of a regulatory unit in the cell.

Question 2

Describe the typicaly eukaryotic gene organization

Answer 2

The structure of a eukaryotic gene contains the upstream regulatory sequences and the promoter sequences, as well as the 5’-UTR upstream of the coding sequence.

The precursor RNA transcript contains the intron and exon sequences, as well as the 5’-UTR and 3’-UTR.

Concurrent with synthesis of the precursor mRNA by RNA polymerase, the transcript undergoes RNA processing to remove intron sequences, add a 5’-cap, and add a 3’-poly(A) tail before being exported from the nucleus to the cytoplasm.

Exons are coding regions and introns are noncoding regions that must be removed.

UTR – untranslated region.

Question 3

Explain the concept of chromosomes

Answer 3

Chromosomes are thread-like structures located inside the nucleus of animal and plant cells during mitosis.

Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA).

Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique.

In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46

Question 4

Overview the cell cycle meiosis (how chromosomes split into daughter cells)

Answer 4

G0: Nondividing state

G1, S, G2: Dividng cells have mitosis pahse and interpahse (chromosomes are amorphus and dispersed)

Prophase of mitosis: chromosomes are condensed and sister chromatid pairs are formed

Question 5

Describe centromeres

Answer 5

Region where the two daughter chromosomes are held together during mitosis
—- after DNA replication but before cell division

Essential for equal distribution of chromosome sets to daughter cells
Link the chromosome to the mitotic spindle

Have AT-rich repeated sequences of ~130 bp

Question 6

Overview meiosis, focusing on what happens between homologous chromosomes

Answer 6

Meiosis I: crossover can occur between homologous chromosomes (recombination)

Meiosis II: separation of homologs into haploid cells

Question 7

What’s the difference between haploid and diploid cells?

Answer 7

Haploid:
Cells with one set of chromosome, e.g. gametes (23 in human cells)

Diploid:
Cells have two sets of chromosomes (23 pairs with 46 in total in human cells)

Question 8

Why is condensation of eukaryotic DNA usefule?

Answer 8

Condensation of eukaryotic DNA into chromosomes reduces the size of the DNA. The assembly of nucleosomes facilitates the tight compaction of mitotic chromosomes.

Question 9

Explain post-translational modifications observed on human histones

Answer 9

Modifications of histone tails by acetylation, methylation, phosphorylation, and ubiquitinylation control chromatin condensation and function.

Histones in a single nucleosome usually contain several, but not all, tail modifications simultaneously.

Histone code: specific post-transcriptional modification combinations in different chromatin regions specifically influence chromatin function by creating or removing chromatin-associated protein binding sites.

Question 9

Describe nucleosomes

Answer 9

Nucleosomes consist of DNA wrapped around histones

Amino-terminal tails of histones stick out, form sites for covalent modification, and form important contacts between nucleosomes.

Covalent modifications of the histones and DNA by cellular enzymes influence whether the DNA is in the more condensed form or not.

Question 10

What’s the difference between euchromatin and heterochromatin?

Answer 10

euchromatin – light-staining, whitish areas – includes most transcribed regions

heterochromatin – dark-staining – includes centromeres, telomeres, and transcriptionally inactive genes

Question 11

Histone modifications play integral roles in chromatin condensation and function. Which of the following is NOT considered to be a histone modification?
- acetylation
- methylation
- phosphorylation

Answer 11

Prenylation is a common lipid modification

Question 12

What is/are true about Philadelphia chromosome

• can be detected by chromosome painting
• involves translocation between the long arm of chromosome 9 and long arm of chromosome 22
• involves translocation between the long arm of chromosome 9 and short arm of chromosome 21
• can be found in chronic myelogenous leukemia

Answer 12

• can be detected by chromosome painting
• involves translocation between the long arm of chromosome 9 and long arm of chromosome 22
• can be found in chronic myelogenous leukemia