BIOLOGY 151 Chapter Notes - Chapter 5: Cell Nucleus, Tryptophan, Nuclear Membrane
13 Jun 2018
School
Department
Course
Professor
REGULATION OF GENE EXPRESSION
â—Ź GENE EXPRESSION: the process of turning on a gene to produce RNA and protein
● It’s more energy efficient to turn on the genes only when they’re required
â—Ź Only expressing a subset of genes in each cell saves space because DNA must be
unwound from its tightly coiled structure to transcribe and translate the DNA
PROKARYOTIC VS EUKARYOTIC GENE EXPRESSION
â—Ź Prokaryotic organisms are single celled organisms that lack a cell nucleus and their DNA
floats freely in the cell cytoplasm
â—‹ When the resulting protein is not needed anymore, transcription stops
â—‹ The primary method to control what type of protein and how much each protein is
expressed in a prokaryotic cell is the regulation of DNA transcription
â—‹ When more protein is needed, more transcription occurs
â—‹ *The control of gene expression is mostly at the transcriptional level
â—Ź Eukaryotic cells have intracellular organelles
○ DNA is contained inside the cell’s nucleus and there it’s transcribed into RNA
â—‹ Newly synthesized RNA is then transported out of the nucleus into the cytoplasm
where ribosomes translate the RNA into protein
â—‹ Transcription and translation are physically separated by the nuclear membrane
â—‹ Transcription occurs only within the nucleus and translation occurs outside the
nucleus in the cytoplasm
â—‹ Regulation of gene expression can occur at all stages of the process
â—‹ EPIGENETIC LEVEL: regulation may occur when the DNA is uncoiled and
loosened from nucleosomes to bind TF
â—‹ TRANSCRIPTIONAL LEVEL: when the RNA is transcribed
â—‹ POST-TRANSCRIPTIONAL LEVEL: when the RNA is processed and exported
to the cytoplasm after it’s transcribed
â—‹ POST-TRANSLATIONAL LEVEL: when the RNA is translated into protein or
after the protein has been made
PROKARYOTIC GENE REGULATION
â—Ź OPERONS: proteins that are needed for a specific function or that are involved in the
same biochemical pathway are encoded in these blocks
â—Ź REPRESSORS: proteins that suppress transcription of a gene in response to an external
stimulus
â—Ź ACTIVATORS: proteins that increase the transcription of a gene in response to an
external stimulus
â—Ź INDUCERS: small molecules that either activate or repress transcription depending on
the needs of the cell and the availability of substrate
â—Ź TRYPTOPHAN: one such amino acid that E coli can ingest from the environment
â—‹ E. coli can synthesize tryptophan using enzymes that are encoded by 5 genes
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Gene expression: the process of turning on a gene to produce rna and protein. It"s more energy efficient to turn on the genes only when they"re required. Only expressing a subset of genes in each cell saves space because dna must be unwound from its tightly coiled structure to transcribe and translate the dna. Prokaryotic organisms are single celled organisms that lack a cell nucleus and their dna floats freely in the cell cytoplasm. When the resulting protein is not needed anymore, transcription stops. The primary method to control what type of protein and how much each protein is expressed in a prokaryotic cell is the regulation of dna transcription. When more protein is needed, more transcription occurs. *the control of gene expression is mostly at the transcriptional level. Dna is contained inside the cell"s nucleus and there it"s transcribed into rna.
