Module 4 : DNA, RNA And Protein Synthasis

Question 1

How is DNA stored in Prokaryotes?

Answer 1

Prokaryotes contain a nucleoid which is a single, circular chromosomal DNA molecule. They also unusually contain one or more plasmid. The DNA within prokaryotic cells is not associated with any proteins.

Question 2

What are plasmids?

Answer 2

They usually only contain a few genes. Plasmids are more accessible for proteins required for gene expression and therefor contain genes that are required often, quickly and in emergencies. The genes for antibiotic resistance are often found in plasmids.

Question 3

What is a chromosome?

Answer 3

Chromosomes are made of one very long condensed DNA molecule associated with proteins.

Question 4

What proteins are associated with the DNA in chromosomes?

Answer 4

The main proteins present are the large positively charged globular proteins called histones, their role is to organise and condense the DNA tightly sot hat is fits into the nucleus.
The other proteins are enzymes used in copying and repairing the DNA.

Question 5

What is chromatin?

Answer 5

The tightly coiled combination of DNA and proteins is called chromatin - this is what chromatids, and therefor chromosomes are made of.

Question 6

What is a centromere?

Answer 6

Where the two chromatids join together found at the centre of the chromosome.

Question 7

What is a chromatid?

Answer 7

During interphase the DNA replicates to create two identical strands of DNA called chromatids joined together at the centromere.the two chromatids that make up the double structure of a chromosome are called sister chromatids. Sister chromatids are identical.

Question 8

What is a telomere?

Answer 8

The ends of chromatids in chromosomes are sealed with protective structures called telomeres.

Question 9

What is the structure of the DNA found in mitochondria and chloroplast?

Answer 9

Similar to the structure of DNA in Prokaryotes.

Question 10

Where is mitochondrial DNA found?

Answer 10

In the matrix of the mitochondria.

Question 11

Where is chloroplast DNA found?

Answer 11

In the stroma of the chloroplast.

Question 12

What is a gene?

Answer 12

A base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule.

Question 13

What are functional RNA molecules?

Answer 13

Molecules required for protein synthesis. Like mRNA, tRNA and rRNA.

Question 14

What is a locus?

Answer 14

The position of a gene on a chromosome.

Question 15

What is an allele?

Answer 15

Each gene can exist in two or more different forms called alleles.

Question 16

What is the triplet code?

Answer 16

Three nucleotide bases code for one amino acid. These are known as codons. These are 20 different amino acids.

Question 17

What us meant by the triplet cod is non-overlapping?

Answer 17

Some triplet base code for start and stop signals. These tell the individual genes where to star and stop. This helps to ensure that the DNA is read correctly and can produce the correct sequence of amino acids.

Question 18

What is meant by the triplet code is degenerate?

Answer 18

There are 4 bases so there are 64 possible different triplets, there are only 20 amino acids that commonly occur in biological proteins. This means that multiple triplet codes can be used for the same amino acid. So the code is said to be degenerate.

Question 19

What are meant by the triplet code being universal?

Answer 19

Almost every o rag sim has the same genetic code. The same codons code for the same amino aids in all living things.

Question 20

What is an intron?

Answer 20

Non coding DNA. This could be gene repeats after a gene or it could be found within genes

Question 21

What is an exon?

Answer 21

Coding DNA

Question 22

What is pre-mRNA?

Answer 22

The whole gene, with both introns and exons.

Question 23

What is splicing?

Answer 23

The process of introns being removed. The coding sections are joined together. The resulting mRNA molecule carries only the coding sequences of the gene. mRNA contains only exons and exits the nucleus before joining a ribosome for translation.

Question 24

What is a genome?

Answer 24

The complete set of genes in a cell. Not every gene is expressed in every cell but hey are present in every cell.

Question 25

What is the proteome?

Answer 25

The full range of proteins that a cell is able to produce.

Question 26

Why is the proteome often larger than the genome?

Answer 26

This is due to the argue amount of post-translational modified proteins. Each gene is capable of producing multiple different proteins by alternative splicing.

Question 27

What is the structure of mRNA?

Answer 27

A single stranded molecule. It is made up of a sugar-phosphate backbone and exposed unpaired bases. Uracil bases are present instead of thymine bases.

Question 28

What is the structure of tRNA?

Answer 28

A single stranded molecule. It has a sugar phosphate backbone. It has a folded shape due to hydrogen bonds between complimentary bases. Amino acids bind to specific region of the molecule. The specific anticodon found on the tRNA molecule is complimentary to a specific codon of an mRNA molecule.

Question 29

What is transcription?

Answer 29

DNA is transcribed and an mRNA molecule is produced.

Question 30

What re the stages of transcription?

Answer 30

1. The stage of protein synthesis occurs in the nucleus 2. Part of a DNA molecule unwinded Cathy listed by helicase, like in DNA replication. 3. This exposes gene to be transcribed. 4. A complimentary copy of the code from the gene is made by building a single-stranded nucleic acid molecule know as mRNA. 5. Free activated RNA nucleotides pair up via hydrogen bonds with their complimentary bases on one strand of the unzipped DNA molecule. 6. The sugar-phosphate groups of these RNA nucleotides are then bonded together by the enzyme RNA polymerase to form the sugar-phosphate backbone of the mRNA molecule. 7. When the gene has been transcribed, the hydrogen bonds between the mRNA and DNA strands break the double-stranded DNA molecule re-forms. 8. The mRNA molecule the leaves the nucleus via a pore in the nuclear envelope.

Question 31

Which way does RNA polymerase move?

Answer 31

From the 5’ to the 3’ of the RNA strand.

Question 32

What is alternative splicing?

Answer 32

The exons of genes can be spliced in many different ways to produce different mature mRNA molecules through alternative splicing. This means that a single eukaryotic gene can code for more than one polypeptide chain. This is part of the reason why the proteome is much bigger than the genome.

Question 33

What is translation?

Answer 33

MRNA is translated and an amino acid sequence is produced.

Question 34

Where does translation take place?

Answer 34

In the cytoplasm of the cell and it involves the use of ribosomes.

Question 35

What are the stages of translation? part 1

Answer 35

1. After leaving the nucleus the mRNA molecule attaches to a ribosome. 2. In the cytoplasm, there are free molecules of tRNA. 3. These tRNA molecules have a triplet of unpaired bases at one end (anticodon) and a region where a specific amino acid can attach at the other. 4. There are at least 20 different tRNA molecules each with a specific anticodon and a specific amino acid binding sight. 5. The tRNA molecules bind with their specific binding site and bring them to the mRNA molecule in the ribosome.

Question 36

What are the stages of translation? part 2

Answer 36

6. The triplet bases on each tRNS molecule pair with a complimentary triplet on the mRNA molecule. 7. Two tRNA molecules can fit onto the ribosome at any one time, bringing the amino acid s that are carrying side by side. 8. A peptide bond is formed between 2 amino acids. 9. This process continues until a stop codon on the mRNA molecule is reached - this acts as a signals for translation to stop and at this point the amino acid chain coded for by the mRNA molecule is complete. 10. This amino acid chain then forms the final polypeptide.

Question 37

How do amino acids form a peptide bond between them?

Answer 37

It is a condensation reaction that requires energy that is given from ATP. The ATP needed for the translation is provide but the mitochondria within a cell.

Question 38

What is a codon?

Answer 38

A sequence of 3 mRNA bases that codes for a specific amino acid. A codon is transcribed from a triplet and it is complimentary to it.

Question 39

What is a mutation?

Answer 39

A change in the DNA base sequence. This means that a codon could code for a different amino acid and the protein could be different or damaged.