Chapter 13 Flashcards
What does RNA do
It transmits genetic information and makes proteins such as antibodies, channels, and enzymes
What is RNA
A nucleic acid with ribose sugar
How is RNA physically different from DNA
RNA is single stranded and uses Uracil instead of Thymine. And has ribose sugar
What are the three types of RNA
mRNA (messenger RNA)
rRNA (ribosomal RNA)
tRNA (transfer RNA)
The shape of the RNA determines its function
Where and how is mRNA made
Made in the nucleus by transcription. Is long, skinny, and straight. never folded
What does mRNA do
Carries the the DNA code (which is the instructions for amino acid assembly) to the ribosome to be made into a polypeptide chain (raw protein)
How many nucleotides are in a codon and what form of RNA are they in
3
And codons are Only in mRNA
What does rRNA do
Wraps around proteins (histo proteins) in the cytoplasm to form the two subunits that make up a ribosome
(Ribbon shape)
What is tRNA
Strand is folded to have two explicit ends. One end has the amino acid
The other end has three nucleotides (called an anticodon)
(Folded shape)
What is an anticodon
Only in tRNA. Made up of 3 nucleotides and it is specific to the amino acid it grabs. Is also complementary to the codon it will attach to (that’s why it’s anti-)
RNA synthesis = ?
Transcription
What is transcription
Segments of DNA (genes) are used as a template to create mRNA. Only copies one gene
(Not copying whole strand of DNA)
Step 1 of transcription
RNA polymerase breaks the DNA hydrogen bonds so the DNA uncoils and opens (the polymerase is specific to nucleic acid)
Step 2 of transcription
RNA polymerase binds to the DNA at a promoter site which is/marks the beginning of a gene
Step 3 of transcription
RNA polymerase brings in complementary nucleotides, building the mRNA, and proofreads
Step 4 of transcription
The DNA is read from 3’ to 5’ (rna is one strand so it is all the “leading strand”), so the mRNA is being built on its 3’ end. There are no Okasaki Fragments or terms of leading/ lagging
Step 5 of transcription
There is also a special end or stop signal/code/codon on the DNA to stop transcription and release the mRNA
Where does transcription take place in eukaryotes and prokaryotes
In eukaryotes it takes place in the nucleus
In prokaryotes it takes place in the cytoplasm
What is pre mRNA
Pre- mRNA will have parts of the gene that is needs and doesn’t need to make the proteins. It takes out from the code what it needs (these sections are called exons)
And leaves what it doesn’t (introns)
The exons will make up mRNA
After mRNA is made where does it go
Out of the nucleus
Exons exit nucleus, introns stay in nucleus (mostly)
Why r introns sometimes left in mRNA
To create different variations of a protein (recording show with or with out certain commercials analogy)
What is a polypeptide
A long chain of amino acids. The sequence determines the shape and function of the protein
A codon wheel or table ONLY refers to which RNA
mRNA (the 3 nucleotides/ codon is what is decoded on the codon wheel/table
How does tRNA and mRNA work together
The tRNA brings the proper amino acid to the mRNA strand by translating the genetic code on the mRNA
What is the genetic code
Universal code
It is the order of three bases/nucleotides at a time on the mRNA. Each 3 is a codon which is made up of a combination of A, U, C, G.
3 nucleotides=1 codon = 1 amino acid
(Is the series of codons)
What is the ONLY start codon
the ONLY start codon is AUG which translates to methionine.
There is only one bc you don’t want to confuse the system
Stop codons
There are multiple stop codons. They stop the polypeptide because there is no anticodon for a stop codon
What is a wobble
Synonymous codons-
Bc Some amino acids have more then one codon that can code for it . They are “synonyms” of each other.
Ex: CAC and CAU both code for Histidine
What is translation
The decoding of an mRNA message into a protein. Happens AT ribosome.
mRNA -> tRNA -> amino acid ->
Polypeptide/ protein
How does translation start
rRNA’s hold proteins in place and locate the beginning of mRNA using chemical attraction (senses cap of the AUG/methionine) so the rRNA will help mRNA get oriented and started in the right direction.
Step one of translation
mRNA attaches to ribosome (cap end) and start codon start codon AUG is read as methionine
Step two of translation
tRNA brings methionine to mRNA. the next tRNA with the 2nd amino acid sits on the mRNA next to methionine. And the previous amino acid (methionine) is peptide bonded to this 2nd amino acid. During this it detaches from its tRNA
Step three of translation
Elongation
The 1st tRNA leaves the mRNA as the 3rd tRNA with its amino acid sit down next to the 2nd amino acid. The 2nd amino acid detaches from its tRNA and peptide bonds to the third amino acid with the first still attached. This is called elongation and repeats until step 3.5
Step 3.5 of translation
Step 3 repeats until a stop codon on the mRNA is reached. Since there is no anticodon/ amino acid for a stop codon the elongation stops
Def. of elongation
The lengthening of the polypeptide chain by adding on amino acids
Step four of translation
Last real step of translation
The stop codon attracts a protein releasing factor (instead of tRNA) and it takes everything apart, so the polypeptide falls of and immediately coils
tRNA let go, mRNA let go, ribosomes break apart back into 2 subunits
Step 5 of translation
End translation start of ribosome building
The new polypeptide may now travel through the ER (endoplasmic reticulum) and/or the GA (golgi apparatus) for post translational modification
(starts back at step 1 of building proteins in ch 7.2 pg 200)
What is the central dogma
In molecular biology it is the information that is passed from DNA to RNA in proteins
Info to run an organisms body.
Starts at DNA, goes to RNA. The pathway is called central dogma
What is Gene expression
Refers to how the action of the proteins creates the characteristics show by the organism
(Gene made or not made)
What are mutations
Changes in the genetic info, code, or sequence of nucleotides in the DNA
that (most) can be passed from generation to generation as the genes on the chromosomes are inherited
(Can be good, bad, neutral, or deadly)
What are somatic changes
Mutations that are not/can not be inherited or passed down to other generations
What are germ line mutations
Mutations that can be inherited
What are point mutations
Mutations that occur or start at a single nucleotide (you can “point” to the start) in the DNA
(3 types)
Point mutation 1: Substitution
Changes only one nucleotide. So it may or may not change only one amino acid
What are frameshift point mutations
Changes the grouping of the nucleotide threesomes. The “reading frame” is shifted. Most cause dramatic, damaging, and/or deadly changes. From the one change on, the amino acids will be different. So the protein will not function normally or at all. (2 types)
Point mutation 2:
Frameshift insertion
Adds one nucleotide into mRNA so that the threesomes are all shifted down/foreword one base and changed. Creating all new codons to be read.
Point mutation 3:
Frameshift deletion
One nucleotide is subtracted or taken out so that all the threesomes following it are shifted back one base. Creating all new codons to be read
What are chromosome mutations
Involve changes in the whole number or structure of a chromosome. Can change the location of genes or even the number of copies of genes
All may or may not affect organism
(4 types)
What are the 4 types of chromosomal mutations
Deletion
Duplication
Inversion
Translocation
Chromosomal mutation 1: deletion
A whole or part of a chromosome “drops out” or is loss
(Part of =gene)
ABCDEF
ACDEF
Chromosomal mutation 2:
Duplication
All or part of a chromosome is repeated, creating an extra copy
(Part of = gene)
ABCDEF
ABBCDEF
Chromosomal mutation 3:
Inversion
Reverses the direction of parts of the chromosome
Genes switch order when chromosome breaks and reattaches
ABCDEF
ACBDEF
Chromosomal mutation 4: translocation
Occurs when one chromosome breaks off and attaches to another. Genes move to other chromosomes when chromosomes break and the bits reattach to other different ones Only for non homologous chromosomes (NOT Crossing over) GH -> ABCDEF ABGHCDEF
What are mutagens
Chemical (pesticides) or physical (sunlight/X-rays) agents in the environment that cause changes in DNA
What causes mutations most of the time
Mutagens
What is polyploid
When all chromosomes go to one side
Can occur naturally but mostly breed.
Happens mostly only in plants
Is good bc it produces bigger, healthier, strong crops
When is a gene expressed
Only when gene is transcribed, made into protein, and protein takes on its function
What is a operon
A group of genes that function together. Their proteins act in concert to achieve a goal
Gene regulation takes place where in prokaryotes?
Cytoplasm
What is a repressor gene
Creates repressor molecules that will be present in the cytoplasm at all times. Is not needed, the repressor is sitting on its “spot” (operator) next to the promoter
Where is repressor gene located
On the operator.
Located all the way to the left and is not part of the operon but will create operon molecule
What is the promoter
Landing spot for mRNA polymerase.
Located between repressor gene and operator
What happened when the repressor is moved
The RNA polymerase can bind to the promoter and transcribes genes
How is the repressor moved using lac example
Lactose molecules change the shape of repressor so it falls of and moves
Takes only 1 or 2 lactose molecules (out of 1000’s) to trigger the repressor so that it can make lax genes to eat the rest
Where does gene regulation in eukaryotes take place
Nucleus
What is the TATA box site
It is next to the promoter and it marks the start of a gene. Marks where mRNA polymerase wants to sit
What is the enhancer
It is before the TATA box and is the binding site (/landing spot) for transcription factors, to enhance the ability of RNA polymerase to bind to the promoter region.
What are transcription factors
Made by the cell to be present in the nucleoplasm. Form a binding site for RNA polymerase. They will bind and release in response to chemical signals (ex: condition of molecules)
Also open up DNA and make DNA flexible
Does every gene have its own enhancer and TATA box
Yes
What is cell differentiation caused by?
Gene expression at various times in development
Why do cells take on special shapes
For specialized jobs
What are homeotic genes
Master control genes
Regulates organs that develop in specific parts of the body
What are homeobox genes
Make transcription factors to turn genes on and off
What are hox genes
Control body plans
Are arranged in the exact order they are expressed
Their function and arrangement is the same in almost all organisms. This is bc almost all animals share the same basic tools for building the different parts of the body
Later become species specific genes and hox die out (before birth?)
Species specific genes
Control what specifically the basic body tools will turn into
Ex: arm bud from hox can turn into arms or wings or fins based on species specific genes.
The arms can then have fingers or paws or hoofs based on more species specific genes
What do all embryos have in common
All embryos share same hox genes
What do transcription factors do
Turn on and off gene products (in charge of gene expression)
What happens to the rest of DNA while one gene is transcribed
It remains in touched
Does the environment influence gene expression
Yes. In some animals it strongly influences the expression of a gene.
If temp is up then the maturation of frogs in the area speeds up
What is the enzyme that binds to DNA during transcription
RNA polymerase
How are the 3 RNAs different
mRNA- carries info from DNA to other parts of cell
rRNA- forms an important part of both subunits of the ribosome
tRNA- carries amino acid to the ribosome and matches them to coded mRNA
