MOL100H23 lecture 10 genes-genomes-chromosomes

Genome

Det komplette settet med genetisk materiale som finnes i en organisme.

DNA sequences

Different types of sequences found in the genome.

Nucleus

The membrane-bound organelle that contains the DNA in a cell.

Chromosomes

Structures made of DNA and proteins that carry genetic information.

Autosomes

Non-sex chromosomes.

Sex chromosomes

Chromosomes that determine the sex of an individual.

Base pairs

The building blocks of DNA, consisting of adenine (A), thymine (T), cytosine (C), and guanine (G).

Protein-coding genes

Genes that contain the instructions for making proteins.

Long noncoding RNA genes

Genes that produce noncoding RNA molecules.

Repetitive DNA

DNA sequences that are repeated multiple times in the genome.

Introns

Noncoding regions within genes.

Untranslated regions (UTRs)

Regions of mRNA that are not translated into protein.

Gene

The entire nucleic acid sequence necessary for the synthesis of a functional gene product.

Transcribed region

The part of a gene that is transcribed into RNA.

Regulatory elements

DNA sequences that control the expression of genes.

Promoter

A region of DNA that initiates gene transcription.

Terminator

A region of DNA that signals the end of gene transcription.

Enhancers

DNA sequences that regulate genes from a distance.

Operon

A group of genes that are transcribed together in prokaryotes.

Monocistronic genes

Genes that produce one mature mRNA encoding for one protein.

Polycistronic genes

Genes that produce one mRNA that gives rise to several proteins.

Alternative splicing

The process by which different exons are included or excluded from the final mRNA transcript.

Intergenic regions

Regions of DNA between genes.

Genome size

The total amount of DNA in an organism's genome.

Gene duplication

The process by which a gene is duplicated, resulting in two copies.

Exon duplication

The duplication of exons within a gene.

Non-coding RNAs

RNA molecules that do not encode proteins.

tRNAs

Transfer RNAs, involved in protein synthesis.

rRNAs

Ribosomal RNAs, involved in protein synthesis.

miRNAs

MicroRNAs, involved in the regulation of gene expression.

Genes

The entire nucleic acid sequence that is necessary for the synthesis of a functional gene product (polypeptide or RNA).

Protein coding genes

Genes that code for proteins.

Polycistronic genes

Genes that have multiple coding regions and produce multiple mRNA/proteins.

Monocistronic genes

Genes that have a single coding region and produce a single mRNA/protein.

Alternative splicing

A process where different combinations of exons are included or excluded from the final mRNA, resulting in the production of different proteins from a single gene.

Gene duplication

The process of creating multiple copies of a gene, leading to the formation of gene families.

Non-coding RNA

RNA molecules that do not code for proteins, such as long non-coding RNA, tRNA, and rRNA.

Repetitive DNA

Approximately 50% of the human genome that consists of repeated sequences.

Simple sequence DNA/Satellite DNA

Repetitive DNA sequences that can be short (1-15 bp) or long (14-500 bp) and are found in specific regions of chromosomes.

Interspersed repeats (transposons)

Repetitive DNA sequences that make up approximately 45% of the human genome and can move within the genome.

DNA fingerprinting

A technique that relies on the differences in repeat lengths of mini-satellites to identify individuals or determine relationships.

Transposable elements

DNA sequences that can move within the genome through a process called transposition.

DNA transposons

Transposable elements that can excise themselves from DNA and re-insert into a new site (cut and paste).

Retrotransposons

Transposable elements that transcribe themselves as RNA, use reverse transcription to generate a DNA intermediate, and insert themselves into a new target site (copy and paste).

Bacterial IS elements

DNA transposons found in bacteria that have a protein coding sequence, inverted repeats, and target-site direct repeats.

Nucleosome

The basic unit of eukaryotic chromatin, consisting of an octamer of histone proteins around which 147bp of DNA is wrapped.

Histone tails

The amino acid extensions of histones that can be chemically modified, such as methylation and acetylation, and play a role in chromatin organization and gene regulation.

Heterochromatin

Regions of chromatin with higher nucleosome density and condensed structure.

Euchromatin

Regions of chromatin with lower nucleosome density and decondensed structure.

Kromatin kondensasjon

Når kromatin er "åpen" eller mindre kondensert (eukromatin), er det mer tilgjengelig for transkripsjon av "aktive" gener. Når kromatin er mer kondensert (heterokromatin), er det mindre tilgjengelig for transkripsjon av "inaktive" gener eller andre områder som ikke transkriberes, som gjentatte elementer.

Eukromatin

Generelt sett er eukromatin mindre kondensert og inneholder "aktive" histonmodifikasjoner som histonacetylering.

Heterokromatin

Heterokromatin er mer kondensert og inneholder "undertrykkende" histonmodifikasjoner som metylering av lysin 9 på histon H3 (H3K9me).

H3K9 metylering i dannelse av heterokromatin

Metylering av lysin 9 på histon H3 (H3K9me3) er viktig i dannelse av kondensert heterokromatin. Histonmetyltransferaser metylerer K9, og proteinet HP1 kan gjenkjenne og binde til H3K9me3. HP1 kan oligomerisere og danne interaksjoner med andre HP1-molekyler, noe som fører til kromatin kondensasjon. HP1 kan også samhandle med histonmetyltransferasen og forårsake mer H3K9me3, og dermed spre heterokromatinet langs kromosomet.

Kromatinorganisering

Kromatinfiberet er arrangert i strukturer i humane celler. DNA er pakket rundt nukleosomer for å danne kromatinfiberet, som deretter danner løkker. Større deler av DNA (ca. 1 MB) er arrangert i topologisk assosierte domener (TADs). Kromatin i en TAD samhandler hovedsakelig med kromatin innenfor TADen enn med kromatin utenfor TADen. Hver kromosom har sin egen plass i kjernen (kalt et kromosomterritorium), men det er fleksibilitet i posisjonen til kromosomene.

Dannelse av kromatinløkker

Kromatinløkker og TADs dannes av SMC-proteiner, for eksempel cohesin. SMC-komplekser danner ringer der DNA kan passere gjennom. Løkker dannes gjennom en prosess kalt "loop extrusion", der cohesin lander på DNA og begynner å passere DNA gjennom seg. Grenselementer stopper cohesin og definerer kantene av løkkene.

Visualisering av løkker

Prober med fluorescerende merker kan brukes til å se hvor langt unna forskjellige DNA-sekvenser er fra hverandre. Dette kan identifisere løkker. For eksempel kan A og B være langt fra hverandre på lineært DNA, men på grunn av løkken overlapper de fluorescerende probene. Visualisering av løkker:A og B, C og F.