Chapter 20 Flashcards
(79 cards)
What are the three consequences of a substitution mutation?
- The formation of one of the three stop codons marking the end of the polypeptide chain. This means the production of the polypetide would be stopped prematurely. The final protein would be different and could not perform it’s final function.
- The formation of a codon for a different amino acid, so a singe amino acid may be different. The protein may differ in shape and may not function properly.
- The formation of a different codon for the same amino acid. This is due to the genetic code being degenerate and so most amino acids have more than one codon. The mutation will have no effect on the polypeptide produced.
What is a frame shift and what consequence does it have?
The deletion of a base will produce a frame shift as the reading frame that conatins each three letters of the code has been shifted to the left by one letter. The gene will be read in the wrong three base group and the coded information will be different. As most triplets will be altered so will most of the amino acids they code for. The polypeptide they produce will be different and most likely lead to a non functioning protein, altering the phenotype.
What is an addition mutation?
An extra base is inserted into the sequence causing a frame shift to the right. If any multiple of three bases are added this frame shift will not happen however teh resulting polypeptide would still be different from one produced by a non mutant gene
What is a duplication mutation?
One or more bases are repeated causing a frame shift to the right.
What is an inversion mutation?
A group of bases are seperated from the base sequence and rejoin but in the inverse order.
What is a translocation mutation?
A group of bases become seperated from the DNA sequence on one chromosome and become inserted on another chromosome. This will often have a significant impact on gene expressions leading to an abnormal phenotype.
Name and describe two mutagenic agents?
- High energy ionising radiation such as alpha and beta particles as well as short wavelength radiation such as x rays and uv light. These can disrupt the structure of DNA
- Chemicals such as NO2 may directly alter the structure of DNA or interfere with transcription.
How can gene mutations arise?
They can arise spontaneously during DNA replication, these occur without any outside interferance. Typically around one per 100 000 genes per generation
What benefits do muations bring?
They produce the genetic diversity needed for natural selection and speciation.
How do chemical mutagenic agents cause damage?
- Can remove groups from a nucleotide such as Nitrous acid. It can remove NH2 from cytosine changing it to uracil.
- Can add groups to nucleotides such as benzopyrene found in tobacco smoke. It adds a group to guanine making itunable to pair with cytosine. When DNA polymerase reaches teh affected guanine it inserts another base.
What type of mutation is caused by benzopyrene?
Substitution gene mutation
How does ionising radiation cause damage to DNA?
They produce free radicals in cells which can alter the shape of bases in DNA so DNA polymerase cannot act on them
How does ultraviolet radiation cause damage to DNA?
Affects thymine in DNA causing it to form bonds with the nucleotides either side of it, disrupting DNA replication.
How does the position of a deletion mutation change the severity of effect it produces?
A delted base at the start of a DNA could alter every triplet in the sequence. A deleted base near the end is likely to have less conseuquences as less triplets will be impacted.
Why do differenciated cells appear diferent from one another?
The proteins that a cell produces are coded for by the genes that are expressed.
What is a totipotent stem cell?
Found in the early embryo and can differenciate into any type of cell.
What is the role of controlling factors?
To conserve energy by ensuring genes that are not required are not expressed.
How are genes prevented from expressing themselves?
By preventing transcription and thus preventing the production of mRNA.
By preventing translation
What are stem cells?
Undifferenciated dividing cells that occur in adult mammal tissues. They can replicate and replace themselves by the process of sel-renewal
What is an embryonic stem cell?
Come from embryos in the early stages development. They can develop into any type of cell in the early stages of development.
What are umbilical cord stem cells?
Derived from the umbilical cord blood, have a similar ability of adult stem cells.
What are placental stem cells?
Found in the placenta and develop into specific typesn of cells.
What are adult stem cells?
Found in the body of the fetus through to adult. Specific to a particular tissue or organ which they produce teh cells to maintain and repair tissue.
What is a pluripotent stem cell?
As divides and matures pluripotent cells are developed. They are found in embryos and can develop into almost any type of cell. Examples include embryonic stem cells and fetal stem cells.
