RNA (4) Flashcards
What is RNA?
RNA is made in the nucleus by DNA. It is involved in protein synthesis.
What is the structure of RNA? (4)
RNA is also a polymer made up of nucleotides, but it differs in structure from DNA in that:
- it consists of a single strand.
- The strand is much shorter than that of DNA.
- The sugar is ribose and not deoxyribose.
- It has three bases in common with DNA adenine, cytosine and guanine but a base called uracil replaces thymine.
What is the function of RNA?
RNA carries instructions from DNA in the nucleus to the ribosomes in the cytoplasm of a cell where it controls the synthesis of proteins from amino acids.
What are the similarities between DNA and RNA? (2)
- DNA and RNA are both made up of: polymers nucleotides that are made up of a sugar (ribose), phosphate and a nitrogen base four nitrogenous bases 2. They are both responsible for the synthesis of proteins.
As you know, DNA is present in the chromosomes in the nucleus of nearly every cell of an organism. Small amounts of DNA, however, are also present in the ____ in the cytoplasm of cells
mitochondria
What is mitochondrial DNA (mtDNA)? (3)
- a double-stranded, ring-shaped molecule found in all mitochondria.
- comes from the egg cell (oocyte) so it is entirely inherited from the mother.
- has its own genome of about 16,500 base pairs that code for proteins (enzymes), tRNA and rRNA. It is therefore much shorter than chromosomal DNA. The genes are essential for the normal functioning of mitochondria, as they code for the enzymes that control cellular respiration.
Why is DNA in mitochondria?
Apparently, mitochondria were originally separate organisms, i.e. prokaryotes. At some point, they entered a symbiotic relationship with eukaryotic cells through endosmosis. As a result, mitochondria contain their own circular mitochondrial DNA or mDNA.
Define prokaryotes.
Prokaryotes = organisms without a nucleus or any other membrane-bound organelle. Most are unicellular bacteria.
Define eukaryotes.
Eukaryotes = organisms with a cell nucleus and many membrane-bound organelles, e.g. animals, plants, fungi and protists.
Explain genetic tracing in relation to mtDNA. (7)
-During fertilization, only the chromosomes from the sperm enter the egg cell (ovum); no other organelles.
-As a result, the organelles, e.g. mitochondria, in the resulting zygote come from the cytoplasm of the egg cell, i.e. from the mother.
-As mtDNA is passed on from generation to generation, it can be used to establish a direct maternal genetic line.
-This means the genes in the mtDNA of the offspring will be the same as the mother’s, the grandmother’s, the great grandmother’s, etc.
-Like all DNA, mtDNA mutates occasionally e.g. substitution can take place where one nucleotide is replaced by another, resulting in a site known as a marker.
-A mtDNA profile of two sets of these markers can be made.
=If the two mtDNA profiles are very similar, the organisms are closely related.
=If the two mtDNA profiles show differences, the organisms will have diverged along different evolutionary pathways.
-These markers can be mapped through generations. This enables researchers to trace lineages through females (matrilineage) and is used to track the ancestry of human groups/individuals back hundreds of generations.
What is mtDNA testing?
If someone is interested to know about his or her family history, a tissue scrape is taken from inside the cheek and sent to any laboratory of genetic genealogy for mtDNA testing. The genetic code is studied at specific locations and the results are compared to the sequence of mtDNA of other individuals or of the reference sample available in the laboratory. This reference sample is called the Cambridge Reference Sequence (CRS) a source of information of human mitochondrial DNA (mtDNA) commonly found in people of European descent. Similar genetic sequences, as shown in the reports of mtDNA testing, indicate a common female ancestor of the individual being tested.
How can mtDNA profiles be used? (3)
mtDNA profiles can be used to:
- family reconstruct maternal-linked relationships.
- investigate forensic cases where the chromosomal DNA is degraded.
- determine if siblings have the same mother.
