Cell Structure and Function - Gene to Protein Flashcards
What is a genotype?
An organisms hereditary information
What is a phenotype?
The observable or physiological traits of an organism
What is gene expression?
The process of going from DNA to a functional products (typically a protein)
What is DNA?
is the heritable material that is used to store and transmit information from generation to generation
What is RNA?
acts as a messenger to allow the information stored in the DNA to be used to make proteins
What is messenger RNA (mRNA)?
is a single-stranded RNA molecule that is complementary to one of the DNA strands of a gene
What is transfer RNA (tRNA)?
carry amino acids to the ribosome. They act as “bridges,” matching a codon in an mRNA with the amino acid it codes for. It’s the physical link between the mRNA and the amino acid sequence of proteins
What do proteins do?
Carry out cellular functions
What are the three stages of gene expression?
Transcription, processing and translation
Where does transcription occur?
In the nucleus
Where does processing occur?
In the nucleus
Where does translation occur?
In the cytoplasm
Why is gene expression regulated at transcription?
Transcription factors need to correctly assemble and DNA needs to be accessible
What is the gene expression regulation at RNA processing?
Capping, extending of polyadenylation (i.e tailing) alternate splicing, producing an mRNA able to be translated
What is the gene expression regulation at translation?
regulatory proteins can block translation, variable mRNA life-spans
Why is controlling gene expression important?
Because it needs to achieve the right thing at the right time (temporal and spatial control)
What are housekeeping proteins?
Proteins continuously produced by DNA
Main features of housekeeping proteins?
Are the more commonly used proteins
Protein and mRNA are present in large quantities (e.g. tubulin)
Typically have long half life in cells
What causes the production of other proteins?
Cell signalling
Features of proteins produced by cell signalling as a response to stimuli?
They are short lived and carry out their required function
What is the 5’ end of DNA?
This is the beginning of the chain and the phosphate group of the first nucleotide sticks out
What is the 3’ end of DNA?
This is the end of the chain where the 3’ hydroxyl of the last nucleotide is exposed
What way are DNA sequences read?
From the 5’ end to the 3’ end
What is transcription?
Transcription is the first stage of gene expression. Genetic information encoded in the base-pair triplets of the DNA molecule is copied to RNA molecules
What are the three steps of transcription?
Initiation, elongation, termination
What is upstream?
The 5’ end of DNA (promotor)
What is downstream
The 3’ end of DNA (terminator)
What does RNA have instead of the T nucleotide?
U (Uracil)
What is RNA polymerase II?
the main enzyme involved in transcription is RNA polymerase
What is the function of RNA polymerase II?
It uses a single-stranded DNA template to synthesise a complementary strand of RNA. Specifically, RNA polymerase builds an RNA strand in the 5’ to 3’ direction, adding each new nucleotide to the 3’ end of the strand
What is the first step of transcription?
Initiation
What are transcription factors (TFs)?
are proteins that bind to DNA so that the RNA polymerase can bind
What is a TATA box?
A promotor sequence of T and A
Where is the TATA box located?
25-35 base pairs upstream of the transcription starting site
What is the function of the TATA box?
It’s recognized by one of the general transcription factors, allowing other transcription factors and eventually RNA polymerase to bind
What are promoters?
are specific nucleotide sequences at the start of a gene (upstream) which signal the initiation of RNA synthesis by assembling a complex that includes RNA polymerase II and one or more transcription factors
What is the initiation process of transcription?
Assembly of several transcription factors is required including the TATA box binding protein (TBP).
Once these proteins have been assembled, RNA Polymerase II can bind to the sequence of DNA (as well as more transcription factors), known as the promoter, to form the transcription initiation complex.
This begins transcription
What is a transcription initiation complex?
RNA polymerase and various general transcription factors bound to the promoter region
What is the second step of transcription?
Elongation
What is the process of elongation?
RNA polymerase II moves in a 3’ to 5’ directions along the DNA strand (template strand) BUT makes mRNA in the 5’ to 3’ direction
As it reads the template strand of DNA, the enzyme builds an RNA molecule out of complementary nucleotides which are added to the growing 3’ end of the transcript
The DNA double helix shape reforms as the transcript leaves the template strand. Transcription continues until terminated by a termination signal
How many nucleotides are exposed at once in elongation in transcription?
10 to 20 nucleotides when DNA is unwound
Is the RNA transcript the same as the non-template strand of DNA?
Yes?? ASK ERINA
What is the third step of transcription?
Termination
What is a terminator?
The ‘stop point’ for transcription
What is processing?
Capping, tailing and splicing
What is capping?
When a modified guanine nucleotide cap is added to the 5’ end of the pre-mRNA strand
The cap helps to protect the mRNA which has to be transported out of the nucleus via the nuclear pores
The guanine cap also provides stability, prevent degradation, assists with translation and aids in transport through the nuclear pores of the cytoplasm.
What is tailing?
When 50 to 250 adenine nucleotides are added to the 3’ end
This provides stability: Increases the redundant code, the longer the tail the longer it takes to degrade the mRNA to reach the coding sequence
Why is capping and tailing done?
They are processes that are thought to facilitate export, confer stability and facilitate ribosome binding in cytoplasm
What is an intron?
Non-coding regions intervening exons
What are exons?
Coding regions (including UTR’s)
What is a UTR?
Untranslated regions at 5’ and 3’ ends
What is the spliceosome and what is its function?
A large complex of proteins and small RNAs
Introns are removed from the transcript and exons are rejoined to form mature mRNA.
Where does splicing occur?
In the spliceosome
What is alternative splicing?
A process in which different combinations of exons are joined together.
Results in the production of multiple forms of mRNA to from a single pre-mRNA
What is a triplet codon?
Three nucleotides on the base sequence coding for an amino acid
