chapter 8 - DNA, genes, and protein synthesis Flashcards
What is a gene
A gene is a section of DNA that contains the coded information for making polypeptides and functional RNA.
Scientist discovered that there must be three bases that code for each amino acid suggest how they came to this conclusion
Only 20 different amino acid’s occur in proteins
Each amino acid must have its own code of bases on the DNA
There are only four different bases in DNA
4 to the power of 3 = 64. which is enough to satisfy the requirements of 20 amino acids.
What is a degenerate code
This means that more than one triplet codes for the same amino acid this reduces the number of mutations.
What is meant by non-overlapping
Each triplet is only read once and the triplets do not share any bases
Where is DNA located in eukaryotes
In eukaryotic cells DNA molecules are found in the nucleus. They are long and linear and associated with proteins called histones To form structures like chromosomes. Mitochondria and chloroplasts contains DNA
What is DNA represented as in prokaryotic cells
In prokaryotic cells DNA is short and circular it is not associated with proteins
What are homologous chromosomes
Chromosome pairs that are approximately the same length, same centromere position, and genes with the same corresponding Loci position. However they can carry different alleles of the same gene.
What is an allele
An allele is described as an alternate form of a gene with every gene existing in two or more possible forms. Each individual inherits two alleles of every gene from their parents.
How is a chromosome formed
The DNA is combined with histones, a DNA-histone complex is coiled. Coils fold to form loops and loops coil and pack together to form the chromosome.
What is a Genome
It is the complex set of genes in a cell including mitochondria and all chloroplasts DNA
what is a proteome
The full range of proteins produced by a genome. This is sometimes called the complete proteome. refers to the proteins produced by a given type of cell under certain conditions.
What is the structure of RNA
Ribonucleic acid (RNA) is a polymer made up of repeating mononucleotide subunits. It’s forms a single strand in which each nucleotide is made up of a pentose sugar (ribose) one of the organic bases and a phosphate group.
Describe the structure of transfer RNA (TRNA)
relatively small molecule made up of around 80 nucleotides. It is a single-stranded chain folded into a cloverleaf shape. At one end there is the point of attachment of an amino acid and at the other end there is an anticodon loop.
Define transcription
A complimentary section of part of the sequence is made in the form of a molecule called pre-mRNA.
Define translation
The mRNA is used as a template to which complimentary tRNA molecules attach amino acids and are linked together to form a polypeptide.
What occurs in transcription
DNA helicase splits the DNA strand. The template strand is used, and complimentary nucleotides from the pool present in the nucleus are joined together to form a pre-mRNA molecule RNA polymerases joins these bases together. adenine binds to uracil not thymine. when RNA polymerase reaches a stop codon it detaches and the production of mRNA is complete.
What happens in splicing of pre-mRNA
In prokaryotic cells transcription results in the production of mRNA from DNA. In eukaryotic cells transcription occurs and results in the production of pre-mRNA which is then spliced to form mRNA. Exons are spliced together and introns are removed from pre-mRNA.
Describe the process of translation
Once the mRNA has diffused out of the nucleus through the nuclear pore. ribosomes attach to the mRNA ready for translation. A ribosome attaches to a starting codon (AUG) at one end of the mRNA. A tRNA molecule with an anti codon (UAG) pairs with the code on on the mRNA. The tRNA carries A specific amino acid in this case it is (methionine) the ribosome moves along the mRNA bringing together to tRNA molecules at any one time. the amino acids are joined by a peptide bond Using an enzyme and ATP. Once the third tRNA molecule binds, the first tRNA molecule is set free to collect another amino acid from the pool. up to 50 ribosomes can pass behind the first so polypeptides can be assembled simultaneously. synthesis stops when ribosome reaches a stop codon.
Assembling a protein after translation
Sometimes a single polypeptide is a functional protein. Often a number of polypeptides are linked together to give a functional protein (quaternary structure)
What is an exon
Coding regions of DNA
What is an intron
Non-coding regions of DNA
what is the definition of a mutation
Changes to the DNA that can arise spontaneously during the replication and changes The base sequence or quantity of DNA.
What is a missense mutation
When the amino acid is changed during a mutation
What is a silent mutation
When the amino acid does not change or the bases code for the same amino acid.
What is a nonsense mutation
When the amino acid is changed to a stop amino acid
What is substitution
When one nucleotide in the DNA sequence is replaced by another, this can either cause a nonsense, misense or a silent mutation.
What is insertion
When one or more nucleotide pairs are inserted into the sequence. This causes a frame shift to the right
What is deletion
When one or more nucleotide pairs or deleted from the sequence. This causes a frame shift to the left
How often does the mutation occur
One in every 100 million bases
What is a small scale mutation
gene mutation
What is a large scale mutation
Chromosome mutations, these can Have whole areas of chromosomes mutated
Causes of mutations
In DNA replication DNA polymerases can add the wrong nitrogenous base to the DNA polymer. Chromosome mutations are changes to the structure or number of whole chromosomes this normally happens in meiosis.
Inheritance of mutations
If a mutation occurs during the formation of gametes then it may be inherited by the offspring. This is important for evolution as it increases genetic variation within a species. If a mutation occurs during mitosis of somatic cells (body cells) then it won’t be inherited by offspring.
What is a mutagen
A chemical or physical biological agent that’s cause mutations
Physical-ionising radiation
Chemical-diminishing agents, creams
Biological-viruses (insert viral DNA into the host cell)
What is a carcinogen
It is a cancer mutagen
Many mutagens can cause mutations in DNA that lead to the host cell becoming cancerous
What is a mutagenic agents and give examples
They increase the frequency/likelihood of mutations
Physical or chemical agents, include high energy radiation exposure, chemicals that alter DNA structure or interfere with the transcription.
What is a proto oncogene
Stimulate appropriate cell division
what is an oncogen
A mutation from proto-oncogens and can lead to uncontrollable cell division
What are tumour suppressor genes
Tumour suppressor genes inhibit cell division, they maintain normal cell division and prevent tumours from developing if these genes become unactivated a tumour can develop.
Why is meiosis important
Meiosis insures that haploid gametes are formed. Therefore they can be combined during fertilisation
meiosis 1 early prophase 1
Chromosomes condense, they become shorter and fatter. Spindle fibres start to form and the nuclear membrane breaks down
meiosis 1 late prophase 1
Spindle fibres are now fully formed, and spread out between centrioles.
meiosis 1 metaphase 1
Pairs of chromosomes line up on the equator the orientation of maternal and paternal chromosomes is random. The pairs of chromosomes could orientate in different ways
meiosis 1 anaphase 1
Maternal and paternal chromosomes move apart and are pulled separately by contraction of the spindle fibres. Each chromosome is attached to one spindle fibre at its centromere. They moved to opposite poles resulting in different combinations of maternal and paternal chromosomes to opposite poles. This is known as independent segregation
meiosis 2 prophase 2
Now the cells are haploid. Chromosomes do not condense at the end of meiosis one, each chromosome still has two chromatids and spindle fibres form again
meiosis 2 metaphase 2
Chromosomes line up on the spindle fibre equator independently
meiosis 2 anaphase 2
Sister chromatids are separate on the spindle. each cell will receive a copy of each chromosome type (it will receive different chromatids) the genes on different chromosomes also undergo independent segregation introducing greater variation
meiosis 2 telophase 2
4 haploid gametes are produced
what are the chromosomes called once they have been crossed over
Recombinance chromosomes
What is the function of the centromere
Spindle fibres attach to the centromere to pull apart chromatids in anaphase.
What is crossing over
Homologous chromosomes crossover at points called Chaisma. The chromosomes break and rejoin exchanging some genes and therefore alleles. This recombination results in genetic variation. It occurs during PROPHASE 1
What is random fertilization
One sperm cell can fuse with any egg cell. there is a random/unique combination of genes in a diploid cell
What is independent segregation/assortment
When cells divide during meiosis, homologous chromosomes are randomly distributed during ANAPHASE 1
Separating independently of each other, this results in gametes having a unique combination of chromosomes.
Why is there a lower abundance of recombinant chromosomes
Because crossing over does not occur that often and only a small number of sections cross over
formula for the number of possible combinations of chromosomes
2 to the power n
n being the number of chromosome in a cell. eg in humans it is 23.
2 to the power of 23 = 8,388,608 Genetically unique gametes through independent assortment alone.
