Lecture 15 - How do genes make cells? Flashcards
How does DNA make you?
Allows cells to do complicated things - respond to the environment, make and break molecules, generate energy and maintain itself
Typical human cell
50% protein
40% lipids
10% carbohydrates
Building blocks
Carbon chains
Sugars
Amino acids
Sugar+base+phosphate
Macromolecules
Lipids
Complex carbohydrates
Proteins
Nucleic acid (RNA/DNA)
Supramolecular assemblies
Membranes
Ribosomes
Chromosomes
Organelles
Nucleus
Golgi
ER
Mitochondria
Every protein has
a specific role in the cell
__________ is the key to life
regulation
What is a gene?
Section of DNA that codes for a protein
Central dogma of genetics
DNA to RNA to Protein
What is transcriptional control?
Determines when and in what cells a gene is transcribed to produce mRNA. It is therefore the first step determining how many individual proteins are produced in a cell.
Why is a brain cell different from a heart cell?
Every cell has the same DNA and the same ~21,000 protein coding genes.
• In any cell type about 11,000 to 17,000 genes are expressed;
• 10,000 of these genes are expressed in all cells (needed for basic cellular functions)
• About 1,000 to 2,000 are unique to a specific cell type – these genes make, say, a brain cell different from a heart cell
The rest are expressed in some but not all cell types
Reason why cells are different is because they have different content/expressions of genes
Transcription
The process where a DNA sequence is copied (transcribed) into an RNA molecule
A gene is said to be ‘turned on’ or ‘expressed’ when it is transcribed.
Transcription is a key control point:
•If a gene is transcribed, it is can used to mak a protein (expressed). - can be translated
•If a gene is not transcribed in a cell, it can’t be used to make a protein in that cell. - cannot be translated
Translation
Process by which mRNA is decoded and a protein is produced
Transcription factors
Are proteins that bind to a specific DNA sequence and control the rate of transcription (DNA to RNA)
Collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription.
Binds very specific parts of DNA, only interact with DNA with specific sequence (10-30 bps can be roughly recognised by a transcription factor)
Transcription factors are proteins that turn genes on and off
How do transcription factors work?
Need activator/s present and repressor absent
Transcription factors then recruit RNA polymerase (get complex formation)
Gene regulation
ability of an organism to control which genes are transcribed in response to the environment
Regulatory regions of a gene
Promoter - the DNA sequence at which transcription factors bind and recruit RNA polymerase. Determines if and how much a gene is transcribed. Contains short sequences that transcription factors bind to.
Transcribed region of a gene
Transcribed region - sequences of DNA that are copied into RNA (transcribed). The transcribed RNA (pre-mRNA) is processed so that it can be translated (e.g. the intron sequences are removed)
contains the information that specifies an amino acid sequence
Two types of transcription factors
Activators and repressors
Activators
Allows transcription to happen by recruiting RNA polymerase to the promoter
Repressors
Prevents transcription from occurring by preventing RNA polymerase from binding to the promoter
Pancreatic beta cell vs liver cell
Pancreatic beta cell Transcription factor (TF) activators for the insulin gene made. TF repressors for insulin gene are NOT made. TF activators for glycogen synthase gene NOT made. TF repressors for glycogen synthase gene is made.
Liver cell
TF activators for insulin gene are NOT made. TF repressors for insulin gene are made. TF activators for glycogen synthase gene are made. TF repressors for glycogen synthase gene are NOT made.
