1. Origin of life. Basic functions and constituents of cells. Flashcards
endosymbiosis
During evolution, a eukaryotic organism, already equipped with adequate cytoskeleton and internal membrane systems for this purpose, engulfed/phagocytosed a prokaryotic organism and they started to live together for their mutual benefit. Mitochondria came about when an aerobic prokaryote performing oxidative phosphorylation was internalized, chloroplasts derived from prokaryotes performing photosynthesis. The origin of peroxisomes is similar.
central dogma
In living systems, the flow of genetic information is unidirectional and follows the path: DNA → RNA → protein → property (phenotype).
transcription
The process in the nucleus by which the genetic information contained in a template strand of DNA is copied into a single-stranded RNA molecule of complementary base sequence (primary/ nascent transcript or preRNA or hnRNA). Transcription is carried out by an enzyme called RNA polymerase. This is the first step in gene expression.
Exon
Exons are sequences of genes that code part of or the entire gene product. In eukaryotes, the exons are separated by non-coding sequences called introns. During transcription, the introns are also transcribed as messenger RNAs, but are subsequently cut out from the transcript before
translation.
intron
A nucleotide sequence in a gene that does not participate in encoding the protein product. Introns occurring in eukaryotes are transcribed in messenger RNS, but are subsequently removed from the transcript before translation.
RNA maturation
Post-transcriptional modifications in eukaryotic cells by which primary transcript RNA is converted into mature RNA. The process includes three major steps: addition of a 5’ end capping, addition of a 3’ poly-adenylation tail, and RNA splicing.
RNA splicing
A post-transcriptional process by which introns are removed and exons are covalently joined to one another as part of generating the mature messenger RNA. In the case of multi-exon genes (i.e., genes containing several exons) exons can be joined in different combinations, leading to different (alternative) matured mRNA strands. Consequently, the proteins translated from alternatively spliced mRNAs will contain differences in their amino acid sequence and, often, in their biological functions. Alternative splicing allows a single gene to code for multiple proteins.
5’ end capping
5’ end capping
A post-transcriptional process by which a specially altered nucleotide (7-methylguanosine tri- or polyphosphate) is added to the 5′ end of the primary RNA transcripts to protect the mRNA from degradation by RNases. It is a part of RNA maturation.
PolyA tailing
A post-transcriptional process by which ~ 200 adenine bases are attached to the 3’end of the synthesized primary RNA transcripts. It is a part of the RNA maturation process. The poly(A) tail is important for the nuclear export, translation, and stability of mRNA.
translation, genetic code
The process in the cytoplasm by which a polypeptide chain is synthesized from an mRNA molecule containing the genetic information. In the cytoplasm, the ribosome reads the sequence of the mRNA bases as triplets. The genetic code describes the relationship between the base triplets and the corresponding amino acids in the polypeptide.
heterotroph
An organism that synthetizes ATP by degradation of organic material produced by other organisms. ATP is used to produce the organism’s own organic compounds and to carry out other cellular processes. All animals, protozoans, fungi, and most bacteria are heterotrophs.
autotroph
An organism which uses the sunlight as energy sources (photosynthetic organism) or produces ATP molecules by simple oxidative processes (chemosynthetic organism). The produced ATP molecules are used to create its own organic compounds by biosynthesis or to carry out other processes of the cells. Plants and certain bacteria are autotroph.
prokaryote
The cell in which there is no real cell nucleus separated from the cytosol by a nuclear membrane. The genetic material of the cell is found in the cell plasma, there are no cell membrane bound organelles or cytoskeleton. Bacteria and cyanobacteria are prokaryotes.
eukaryote
Those living organisms that have in their cells a nucleus separated by a membrane from the cell plasma, have a structured internal membrane system (nuclear membrane, endoplasmic reticulum, mitochondria, etc.) and cytoskeleton. Most of the organisms belong to this group
(unicellular eukaryotes, plants, animals, fungi).
primary biogenic elements
Primary biogenic elements include carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and phosphorus (P). They constitute 98% of the cells, which is explained by the fact that these elements form the bulk of the organic matter of living organisms, and H and O also form water.
