Chapter 6- Transcription and translation (1) Flashcards
What are histones?
Histones are proteins that coil and structure the DNA of eukaryotic cell nuclei into units called nucleosomes.
What does the histone octamer consist of?
Consists of 2 copies of each histone protein.
How many times does DNA coil around the octamer to form the nucleosome?
Twice
What does a nucleotide consist of?
It consists of a nitrogen containing base connected to a 5-carbon sugar (Pentose sugar) and a phosphate group.
What can the sugar be in a nucleotide?
1- Ribose = RNA
2- Deoxyribose = DNA
What part of the nucleotide is the structural element?
The sugar and phosphate of a nucleotide
What are the four possible nitrogenous bases available in DNA?
1- Adenine (A)
2- Thymine (T)
3-Cytosine (C)
4- Guanine (G)
What are the four possible nitrogenous bases available in RNA?
1- Adenine (A)
2- Uracil (U)
3-Cytosine (C)
4- Guanine (G)
Bases are classed as what?
Purines or pyramidines
What are the properties of purine and what bases are purines?
Purines contain two interlocking nitrogen containing rings.
Purines are adenine and guanine.
What are the properties of pyramidines and what bases are pyrimidines?
Pyrimidines contain a single nitrogen containing ring.
Pyrimidines are cytosine and thymine.
How do nucleotides join together?
When nucleotides join together, a condensation reaction takes place and a phosphodiester bond is formed.
This occurs between the carbon of one nucleotide and the phosphate group of the nucleotide.
In DNA, how are bases on different strands held together?
They are held together by H-bonds
How many hydrogen bonds are required to join each DNA base pairings together?
Adenine always pairs with thymine by 2 hydrogen bonds.
Cytosine always pairs with guanine by 3 hydrogen bonds.
What are the properties of the DNA double helix?
Two helical polynucleotide chains are coiled.
Complementary bases are held together by hydrogen bonds on the inside.
The individual hydrogen bonds are weak but the large number of them makes it stable.
What does mitochondrial DNA do?
Encode the mitochondrial proteins and some ribosomal RNA.
What does the mitochondrial DNA contain?
It contains genes to direct the synthesis of enzymes involved in oxidative phosphorylation (ATP production)
Contains genes for synthesis of transfer RNA (tRNA)
Contains genes for synthesis of ribosomal RNA (rRNA)
These RNA’S help assemble amino acids into functioning proteins.
What is RNA?
RNA is a sequence of nucleotides.
What are the fundamental differences between RNA and DNA?
1- RNA has a ribose sugar rather than deoxyribose
2- RNA is single stranded
3- Uracil instead of thymine
Which RNA bases are purine and which ones are pyrimidines?
Purines in RNA = Adenine and guanine
Pyrimidines in RNA = Cytosine and uracil
What is transcription?
Transcription- the production of messenger RNA (mRNA) by the enzyme RNA polymerase, and the processing of the resulting mRNA molecule.
What are the 4 steps of transcription?
1- Initiation
2- Elongation
3- Termination
4- Processing
Explain the process of initiation?
The DNA molecule unwinds and separates to form a small open complex.
RNA polymerase (enzyme) binds to the promoter of the template strand.
Promoter regions- found at the beginning of the gene.
The promoter region contains sequences of thymine’s and adenine’s which is referred to as the TATA box.
TF = transcription factors- binds to the TATA box (promoter region) when signalled to.
RNA polymerase II is an enzyme that binds and opens up the DNA double helix and starts to read the information from the genetic code.
Explain the process of elongation?
RNA polymerase II moves along the template strand, synthesising an mRNA molecule.
Explain the process of termination?
Involves the addition of additional adenine nucleotides at the termination site of the RNA transcript.
The process of adding additional adenine nucleotides is called polyadenylation.
Explain the process of processing?
Once transcription is terminated, the RNA molecule is then processed as follows:
Genes are composed of coding sequences (exons) interrupted by non-coding sequences (introns).
RNA splicing removes introns.
Messenger RNA (mRNA) is then produced which then leaves the nucleus through the nuclear pores.
