Module 4 : DNA, RNA And Protein Synthasis Flashcards
How is DNA stored in Prokaryotes?
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.
What are plasmids?
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.
What is a chromosome?
Chromosomes are made of one very long condensed DNA molecule associated with proteins.
What proteins are associated with the DNA in chromosomes?
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.
What is chromatin?
The tightly coiled combination of DNA and proteins is called chromatin - this is what chromatids, and therefor chromosomes are made of.
What is a centromere?
Where the two chromatids join together found at the centre of the chromosome.
What is a chromatid?
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.
What is a telomere?
The ends of chromatids in chromosomes are sealed with protective structures called telomeres.
What is the structure of the DNA found in mitochondria and chloroplast?
Similar to the structure of DNA in Prokaryotes.
Where is mitochondrial DNA found?
In the matrix of the mitochondria.
Where is chloroplast DNA found?
In the stroma of the chloroplast.
What is a gene?
A base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule.
What are functional RNA molecules?
Molecules required for protein synthesis. Like mRNA, tRNA and rRNA.
What is a locus?
The position of a gene on a chromosome.
What is an allele?
Each gene can exist in two or more different forms called alleles.
What is the triplet code?
Three nucleotide bases code for one amino acid. These are known as codons. These are 20 different amino acids.
What us meant by the triplet cod is non-overlapping?
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.
What is meant by the triplet code is degenerate?
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.
What are meant by the triplet code being universal?
Almost every o rag sim has the same genetic code. The same codons code for the same amino aids in all living things.
What is an intron?
Non coding DNA. This could be gene repeats after a gene or it could be found within genes
What is an exon?
Coding DNA
What is pre-mRNA?
The whole gene, with both introns and exons.
What is splicing?
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.
What is a genome?
The complete set of genes in a cell. Not every gene is expressed in every cell but hey are present in every cell.
What is the proteome?
The full range of proteins that a cell is able to produce.
Why is the proteome often larger than the genome?
This is due to the argue amount of post-translational modified proteins. Each gene is capable of producing multiple different proteins by alternative splicing.
What is the structure of mRNA?
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.
What is the structure of tRNA?
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.
What is transcription?
DNA is transcribed and an mRNA molecule is produced.
What re the stages of transcription?
- The stage of protein synthesis occurs in the nucleus
- Part of a DNA molecule unwinded Cathy listed by helicase, like in DNA replication.
- This exposes gene to be transcribed.
- A complimentary copy of the code from the gene is made by building a single-stranded nucleic acid molecule know as mRNA.
- Free activated RNA nucleotides pair up via hydrogen bonds with their complimentary bases on one strand of the unzipped DNA molecule.
- 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.
- When the gene has been transcribed, the hydrogen bonds between the mRNA and DNA strands break the double-stranded DNA molecule re-forms.
- The mRNA molecule the leaves the nucleus via a pore in the nuclear envelope.
Which way does RNA polymerase move?
From the 5’ to the 3’ of the RNA strand.
What is alternative splicing?
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.
What is translation?
MRNA is translated and an amino acid sequence is produced.
Where does translation take place?
In the cytoplasm of the cell and it involves the use of ribosomes.
What are the stages of translation? part 1
- After leaving the nucleus the mRNA molecule attaches to a ribosome.
- In the cytoplasm, there are free molecules of tRNA.
- 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.
- There are at least 20 different tRNA molecules each with a specific anticodon and a specific amino acid binding sight.
- The tRNA molecules bind with their specific binding site and bring them to the mRNA molecule in the ribosome.
What are the stages of translation? part 2
- The triplet bases on each tRNS molecule pair with a complimentary triplet on the mRNA molecule.
- Two tRNA molecules can fit onto the ribosome at any one time, bringing the amino acid s that are carrying side by side.
- A peptide bond is formed between 2 amino acids.
- 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.
- This amino acid chain then forms the final polypeptide.
How do amino acids form a peptide bond between them?
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.
What is a codon?
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.
What is a mutation?
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.
