Chapter summary
Genomes and gene regulation, at a glance
Scan the key ideas, or hide the answers and try to recall them.
01
Compare three kinds of genome
Does every genome consist of linear double-stranded DNA?
Key idea and reminders
Genome organisation varies in molecule type, strandedness, size, packaging and gene structure; avoid treating one model as universal.
- Typical bacterium: compact circular DNA.
- Eukaryotic nucleus: linear histone-associated chromosomes.
- Viruses vary in DNA/RNA, strandedness and segmentation.
Keep in mind: Viral genomes are diverse and can be RNA, segmented or linear as well as DNA and circular.
02
Non-coding does not mean useless
How can DNA influence a cell without encoding a polypeptide?
Key idea and reminders
Non-coding regions can control expression, support chromosome segregation or protect chromosome ends.
- Promoter/enhancer/silencer: expression control.
- Centromere: segregation machinery.
- Telomere: chromosome-end protection.
Keep in mind: Regulatory and structural DNA can affect expression, segregation and chromosome stability.
03
Make a gene accessible
Why can two cells with the same DNA transcribe different genes?
Key idea and reminders
Chromatin state changes access to DNA, allowing stable but potentially reversible differences in gene expression.
- Accessible chromatin favours factor binding.
- Histone acetylation often supports access.
- DNA methylation can promote transcriptional repression.
Keep in mind: Chromatin and methylation changes can regulate expression without changing the base sequence.
04
Switch transcription up or down
How can a distant enhancer influence a promoter?
Key idea and reminders
DNA control elements bind proteins that recruit or inhibit transcription machinery; DNA looping can connect distant sites.
- Control elements are DNA; factors are proteins.
- Enhancers can work through DNA looping.
- Combinations of factors support tissue-specific expression.
Keep in mind: An enhancer is a DNA sequence; an activator is a protein that can bind it.
05
Regulate RNA and protein after transcription
Why can equal transcription rates produce unequal protein amounts?
Key idea and reminders
Protein output depends on RNA processing and lifetime, translation efficiency, and the activity and lifetime of the protein itself.
- RNA lifetime changes available message.
- Translation initiation changes use of each message.
- Modification and degradation change protein function and duration.
Keep in mind: RNA use and decay, protein modification and protein degradation provide additional control.