Genetics Flashcards
Nucleus Structure
Surrounded by a nuclear envelope to separate it’s nucleoplasm from the cytoplasm.
Nuclear Envelope 10% composed of pores
Nucleus Contains
- Ions
- Enzymes
- RNA and DNA nucleotides
- Small amounts of RNA and DNA
- Filaments (matrix) fill the Nucleoplasm and help provide structure
- Nucleoli- organelles that synthesize rRNA. Large # of nucleoli = large # of proteins formed
Nuclear Pores
10% of nuclear envelope
Active transport (require energy/ATP)
Macromolecules energy dependent: proteins into nucleus, mRNA out to cytoplasm
Small molecules passively passive
Selective b/c we don’t want incorrect/uneditted mRNA going into cytoplasm
Pores may e open or closed
DNA vs. RNA
DNA: double stranded, thymine, deoxyribose [NO uracil], made via DNA replication
RNA: single stranded, uracil, ribose [NO thymine], made via transcription
triplet vs codon vs anticodon
triplet = 3 DNA bases (in nucleus)
codon = 3 mRNA bases (starts in nucleus and travels to cytoplasm/ at ribosome)
anticodon = 3 tRNA bases (in cytoplasm/ at ribosome)
RNA polymerase
Enzyme in transcription (using DNA to create RNA)
Finds TATA box to start/activate transcription
Unwinds DNA 2 turns at a time….DNA wil then rewind due to it’s high affinity for itself
Always present in nucleus but not always activated
Moves along DNA until it reaches a chain terminating sequence
Operon
Controls synthesis of a nonprotein intracellular product.
The promotor has an affiinity for RNA polymerase for transcription
The repressor prevents attachment of RNA polymerase - it is only activated when there is sufficient amount of the produced enzyme in the cytoplasm
Negative feedback
Nucleotide Binding
DNA:
Adenine binds with Thymine
Cytosine binds with Guanine
[Apples on a Tree]
[Cars in the Garage]
4 nitrogenous bases: deoxydenalic acid, deoxythymidylic acid, deoxyguanylic acid and deoxyxytidylic acid
Molecules and their units
DNA, transcribed DNA, mRNA, tRNA, protein
DNA - triplet (ex: T-C-T)
transcribed DNA strand - triplet (ex: A-G-A)
mRNA - codon (ex: A-G-A)
tRNA - anticodon (ex: U-G-U)
Protein - amino acid (ex: Arginine)
Transcription vs. Translation
Transcription:
DNA produces RNA
In nucleus
RNA polymerase = enzyme
DNA helix temporarily “CRIPpled”
Translation:
RNA codes for a protein
In the cytoplasm (@ the ribosome)
Ribosomes “LAy” around the cytoplasm and on the RER
Protein Synthesis Analogy
Food
Story: Friend made a cupcake I really liked so I wanted to make it at home. I only wanted the cupcake recipe so I didn’t need to copy her entire cookbook. I just copied the one cupcake recipe while at her house.
Nucleus = friends house (location of DNA)
DNA = cookbook (entire genome)
Transcription = copying one recipe from the cookbook (copying the code for a gene from DNA onto RNA)
mRNA = the copied recipe (code for a protein)
Story: I go home with the recipe and decide to make the cupcakes at my house. I have helpers bring me the ingredients I need as I follow the recipe line by line. When the cake batter is all mixed together I put the cupcakes in the oven to complete the baking of the cupcakes.
Cytoplasm = my house (location of ribosomes - free-floating or on RER)
ribosome = chef reading the recipe one line at a time (ribosome reads one codon at a time)
tRNA = chef’s helper (brings the appropriate amino acid to the ribosome based on the codon)
amino acid = single ingredient (building block of the protein)
protein = complete cupcake batter (protein…which then goes to ER/golgi apparatus for final folding/packaging)
RER/Golgi Apparatus = oven to complete the baking of the cupcake (location to complete the folding/modifying of the protein)
Types of RNA
ALL
PRECURSOR MESSENGER RNA (pre-mRNA)- Immature single strand processed in nucleus to form mRNA. Contains Introns & Exons (b/c not editted by spliceosomes yet). In Nucleus.
SMALL NUCLEAR RNA (snRNA)- Directs splicing of pre-mRNA to make mRNA. In nucleus.
MESSENGER RNA- Carries genetic code to cytoplasm (chain of exons, EXiting the nucleus). Starts in nucleus and goes to cytoplasm.
TRANSFER RNA (tRNA)- Transports activated amino acids to the ribosomes. tRNA matchs to appropriate mRNA via complementary anticodon (tRNA) and codon (mRNA). In cyotoplasm.
RIBOSOMAL RNA- Along with 75 other proteins, forms ribosomes, the structures which create proteins
MICRO RNA (miRNA) (currently HOT research topic)- Single strands of 21 to 23 nucleotides regulating transcription and translation
Modulator (idea of elephant on a teeter totter, part of feedback mechanism)… Introducing this important concept…..
pre-mRNA
PRECURSOR MESSENGER RNA (pre-mRNA)- Immature single strand processed in nucleus to form mRNA. Contains Introns & Exons (b/c not editted by spliceosomes yet). In Nucleus.
snRNA
SMALL NUCLEAR RNA (snRNA)- Directs splicing of pre-mRNA to make mRNA. In nucleus.
mRNA
MESSENGER RNA- Carries genetic code to cytoplasm (chain of exons, EXiting the nucleus). Starts in nucleus and goes to cytoplasm.
tRNA
TRANSFER RNA (tRNA)- Transports activated amino acids to the ribosomes. tRNA matchs to appropriate mRNA via complementary anticodon (tRNA) and codon (mRNA). In cyotoplasm.
rRNA
RIBOSOMAL RNA- Along with 75 other proteins, forms ribosomes, the structures which create proteins
miRNA
ALL
MICRO RNA (miRNA) (currently HOT research topic)- Single strands of 21 to 23 nucleotides regulating transcription and translation
Modulator (idea of elephant on a teeter totter, part of feedback mechanism)… Introducing this important concept…..
The ultimate measure of gene expression is….
“The ultimate measure of gene “expression” is how much protein is produced because proteins carry out cell functions specified by the genes.” ~Hall
Controlling genetic error
With all of the codons and transcriptions going on there is a great chance of ERROR.
Genetic regulation and enzymatic regulation help control and prevent these errors
Micro RNA edits and may repress or enhance gene expression
Transcription
Steps 1-5
Location = nucleus
Step 1: RNA polymerase recognizes promotor region on DNA. This initiates activation and DNA strands unwind.
Step 2: RNA polymerase causes 2 stands of helix to unwind at a time.
Step 3: New RNA nucleotides (codons) match with DNA (triplets) and a new RNA chain is created until RNA polymerase identifies the terminating sequence/terminator region. Note: DNA rewinds itself after RNA polymerase has passed due to DNA having a high affinity for itself.
Step 4: RNA molecule (pre-mRNA) is released into nucleoplasm where spliceosomes will splice the pre-mRNA and create mature mRNA (the exons). The INtrons will stay IN the nucleus and degrade as they are non-protein coding pieces.
Step 5: The mature/editted mRNA exits via nuclear pore (active transport) into the cytoplasm in search of a ribosome (for translation)
Introns vs Exons
pre-mRNA: chain of introns and exons
mRNA = exons only
INtrons stay IN the nucleus and get degraded. They are non-protein pieces.
EXons will EXit the nucleus b/c they contain protein coding info.
Translation
Steps 6-12/”13”
Step 6: The start codon (mRNA) signals the beginning of translation when the small ribosomal subunit attaches upstream of the AUG start codon.
Step 7: tRNA brings an AA over to the ribosome.
Step 8: Complementary pairing occurs between codon (mRNA) and anticodon (tRNA)
Step 9: Once the initial tRNA anticodon attaches to AUG codon (mRNA) the large ribosomal subunit attaches, creating the translation complex. (Initiation is complete). Note: the large subunit has 3 sites: E (exit), P (polypeptide chain), A (arrival).
Step 10: The complex slides down the mRNA and the “empty” tRNA (no more AA) leaves from the E site (think Exit site).
Step 11: Once a stop codon (UAA, UAG, UGA) is identified, a release factor attaches to the A site and the polypeptide chain is released from the P site.
Step 12: The entire compelx dissociates and can reassemble at any point when a start codon (AUG) is identified on mRNA.
“Step 13” - the polypeptide chain folds or may need to be modified with the help of the ER and golgi apparatus/body.
Ribosome sites/regions
3 sites on large subunit = EPA
E site = exit site. This is where the “empty” tRNA exits the ribosome since it’s AA is no longer attached
P site = polypeptide site. This is where the polypeptide chains grows as AA are added one by one
A site = arrival site. This is where a “full” tRNA (carrying an AA) initially binds
Translation and energy
This process takes a lot of energy (lots of ATP).
Can also create polypeptides that become ribosomes (attached to RER or free-floating in cytoplasm)
