27 March, 2014 nuary, 20 NAME: Cell and Molec Test 2 Part A. Multiple Choice. 30

Question

27 March, 2014 nuary, 20 NAME: Cell and Molec Test 2 Part A. Multiple Choice. 30 questions, 2 points each. It is fine to write on this part of the test, but it is the scantron answer that countsll 10 March, 2017 t the N y by s A1. Each nucleosome core particle contains- different types of histone proteins for a total of protein molecules. A2. At the beginning of mitosis, when karyotypes are made, there are the chromosomes (homologs), each containing double-stranded ONA molecule(s). of each of a. Two; one b. two; two c. two; four d. four; one e. four; two A A3. During translation, ribosomes move in the_ , direction on the mRNA and proteins are synthesized in the direction >a. 5' to 3; N terminal to C terminal b. 5' to 3'; C terminal to N terminal c 3' to 5'; N terminus to C terminal d. 3' to 5; C terminal to N terminal e. 5' to 3'; 3' to 5" C A4. The promoter is needed to bind so that can occur a. RNA polymerase; translation b. ribosomes; translation C. RNA polymerase transcription d. ribosome; replication e. RNA polymerase; replication AS. All of the following contain BOTH RNA and protein EXCEPT b. snRNPs for splicing d. small ribosomal subunit a. nucleosomes c. large ribosomal subunit e.polysomes A6. Which of the following occurs "upstream" of the transcription start site in prokaryotic genes? a. Ribosome binding site b. 5' UTR c. promoter d. start codon e. terminator A 7. Histone proteins contain a lot of , an amino acid that is often in nucleosomes that are associated with active genes. a. methionine; phosphorylated b. Serine; methylated c. Aspartic acid; phosphorylated d. Lysine; acetylated

Explanation / Answer

A1) D. 4;8

In eukaryotes, the DNA is packed in the form of nucleosomes and they are basic units of chromatin. Each and every nucleosome has 146 base pair double-stranded DNA which wrapped around a histone octamer. Each histone octamer made up of two copies of H2A, H2B, H3 and H4 histones. Each nucleosome connected to another nucleosome by linker DNA which attached to another histone called H1. Among all histones, H3 and H4 are highly conserved. All histones posses the basic amino acids which neutralize the negative charge of DNA and cause the stabilization of DNA within the cell.

A2) C. two; four

Mitosis is a type of cell division in which the 2 daughter cells possess the same number of chromosomes as that of the parent cell. The cell cycle consists of interphase and mitotic phase. The interphase divided into G1, S, G2 phases. In S phase or synthetic phase of the cell cycle, the chromosomes are duplicated i.e. the new daughter DNA copies are produced from the parental DNA. Each duplicated chromosome has two copies of double-stranded DNA which are attached to the centromeric region. In diploid organisms possess two copies of each chromosome so in S phase each copy of chromosome synthesise new copy, so after the S phase or at the beginning of mitosis two chromosomes posses the four double-stranded DNA molecules (e.g. chromosome 1(1st copy) ; 2 dsDNA attached at centromere + chromosome 1 (2nd copy) ; 2 dsDNA attached at centromere).

A3) A. 5’ to 3’; N terminal to C terminal

The information about the amino acid sequence of a protein is present in DNA. The RNA polymerase bind to the promoter sequences of DNA and copy the information present in DNA into mRNA by transcription processes and then ribosome's translated this information located in mRNA (in the form of codons) as a protein by a process called translation. The amino acid sequence information on mRNA present in the form of codons. The ribosomes bind to the mRNA translates its information in 5’ to 3’ direction. During the translation initiation, the charged formyl methionyl tRNA bind to the P-site of the ribosome and second charged tRNA bind to the A-site. During the elongation step, the ester bond between the formyl methionine and tRNA is cleaved and the carboxylic group of formylmethionine amino acid nucleophilically attacks the amino group of next charged amino acid which is located at A-site and a peptide bond is formed by the peptidyl transferase activity of large ribosome. During the elongation the ribosomes move in 5’ to 3’ direction on mRNA, synthesize the polypeptide and the N-terminal end of the polypeptide is released into the cytoplasm.

A4) C. RNA polymerase; Transcription

All the proteins which expressed in a cell are coded by the genes which are present in DNA. The RNA polymerase bind to the promoter sequences of DNA and copy the genetic information present in DNA into mRNA by transcription processes and then ribosome's translated this information located in mRNA (in the form of codons) as a protein by a process called translation. The template DNA strand or negative strand or nonsense strand of DNA is complementary to mRNA. The RNA polymerase binds to the promoter region which is located at an upstream portion of a gene and initiates the synthesis of mRNA by denovo fashion. From the transcription bubble (DNA-RNA hybrid), 5 end of mRNA is released into nucleoplasm during transcription processes.

A5) a. Nucleosomes

The nucleosomes are basic units of eukaryotic chromatin consist of dsDNA and histone proteins but not RNA but remaining all possess the RNA.

A6) B. 5’UTR (The 5 untranslated region)

The 5 untranslated region is also referred to as leader sequence/leader RNA located upstream to the promoter region of RNA. The several regulatory proteins bind to the 5’UTR of RNA and regulate the transcription and translation of a protein. The length of 5’UTR in prokaryotes is 3-10 nucleotide long but in eukaryotes, it is 100 to several 1000 nucleotides. In prokaryotes, the 5’UTR has the Shine Dalgarno sequence which acts as a ribosome binding sites but in eukaryotes has Kozak consensus sequence which is similar to the Shine Dalgarno sequence of the prokaryotes.

A7) Lysine; acylated

In eukaryotes, the DNA is packed in the form of nucleosomes. Each and every nucleosome has 146 base pair double-stranded DNA which wrapped around a histone octamer. Each histone octamer made up of two copies of H2A, H2B, H3 and H4 histones. All histones posses the basic amino acids such as lysine. It posses the positive charge which is used to neutralize the negative charge of DNA and cause the stabilization of DNA within the cell. For the expression of a gene in DNA, it must be destabilized by the addition of acylated groups to the lysine amino acid. Acyl group has the negative charge which interacts with the negative charges of DNA and destabilizes the DNA.

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