Unit 2 test (Ch. 10-15) Flashcards
What is a gene?
It’s a discrete unit of hereditary info
what does a gene consist of?
consist of a specific nucleotide sequence in DNA
What kind of DNA sequences make proteins?
Coding DNA sequences
What kind of DNA sequences make funbctional RNA molecules?
Non-coding DNA sequences
What is a genome?
Genetic material of organisms/virus, including non-coding DNA sequences
True or false?
Genome size corresponds with the number of genes in an organism/virus.
False. It does not correlate with the number of genes.
approximately how many genes in a genome?
21,000
What has the lowest coding gene density due to large amount of non-coding dna
Mammals
what is the structure of DNA in Eukaryotic cells?
Form of Chromatin
What are DNA molecules bound to in eukaryotic cells?
special proteins called Histones
when DNA and histones condense… it’s called?
chromatin
what is an example of a histone?
H2A, H2B,H3,H4
Why is DNA bound to histones?
to condense into chromatin and protect it.
what is a nucleosome?
DNA wrapped around a histone
what are the 2 types of chromatin?
Euchromatin and heterochromatin
what is euchromatin?
loose and found througout the nucleus when cell divides (not easily visible)
Genes can be expressed in this form. Which chromatin is it?
Euchromatin
why can euchromatin allow genes to be expressed?
because the genome is active
what is heterochromatin?
Tightly packed, darkly stained and found close to nuclear membrane.
why cant genes be expressed in heterochromatin?
because a portion of the genome is inactive so that portion of the genome will not be able to express it’s genes.
what loosens the euchromatin?
acetyl groups on histones
what causes the heterochromatin to condense?
Deactylation and presence of methyl groups on cytosine
How do histones condense chromatin? (Turn into heterochromatin?)
-Since DNA is -ve and histones are +ve
-they attract.
-acetylation removes the =ve charge on histones to loosen
-methylation of cytosine can help recruit proteins to the area that will help condense chromatin
what is Epigenetics?
the process of activating and deactivating genes through chemical modification
what roles does epigenetics involve? (4)
-cell specialization
-oncongentics process (cancer)
-disease
-development
what is the central dogma?
It is a theory stating the genetic info flows through DNA molecules to RNA to proteins.
What is gene expression?
Process where a gene is turned on in a cell to make RNA and proteins: 2 steps are transcription and translation
what does gene expression use and what do the used things do?
uses: mRNA, rRNA, tRNA
do: translates genetic language into protein language
what is the minimum number of nucleotides used to generate amino acids diversity?
3 (4^3=64)
what is the smallest unit of length that can code for all amino acids?
triplets of nucleotide bases (4^3)
what are the genetic instructions for a polypeptide?
DNA is written as a series of non-overlapping, 3 nucleotide words
What are the 3 nucleotide words called?
Triplet codes which are codons
The anatomy of a gene: what is the form of DNA?
Chromatin
The anatomy of a gene: what is a gene specifically?
Stretches of DNA that codes for proteins (coding DNA)
The anatomy of a gene: gene expression relies on something important? What is it?
It depends on the Regions of DNA
The anatomy of a gene: What is the promoter?
Region where the protein binds to when a gene is going to be expressed
What is a gene region that will be transcribed called?
Coding region
What does a coding region consist of (2 points)?
-Star point
-Termination sequence
At the termination point, how does the transcription stop?
A short codon stops the transcription
What does non-coding DNA include?
Sites of genes that make functional RNA or regions of DNA with other functions
What type of DNA is a genome composed of?
Non coding DNA but excluding genes that make functional RNA
What type of DNA does transcription and translation of a DNA sequence use?
non coding DNA
Sites of non coding DNA regions?
Genome, gene expression, centromeres, telomeres
What is a telomere and centromere?
Telomere are the ends of a chromosome which eukaryotes have evolved special non coding DNA sequence to protect the genes from being eroded.
The centromere are where the spindle fibres attach to the chromosome during cell division
Do telomeres contain genes or genomes?
Neither. Telomeres contain specific DNA sequences and proteins that protect genomes by postponing the erosion of genes located at the ends of the dna molecules
What is the telomeres for humans? Where is it found?
Found at the 6th nucleotide sequence: TTAGGG
Do telomeres shrink or grow after cell division?
Shrink
What catalyses the lengthening of telomerase in stem cells?
Telomerase
What does an organism have to do to lead a specific trait by dictating the synthesis of proteins or RNA molecules?
Organism must inherit DNA
Where does transcription start in a eukaryotic cell?
The nucleus
What is the main purpose of transcription?
To use the genetic info in the form of dna as a template strand to generate a the molecule of rna
What are the stages of transcription?
-initiation
-elongation
-termination
What happens in initiation of transcription?
-transcription factors inhibit promoters (region to be transcribed) (collection of proteins) mediate binding of RNA polymerase II.
-RNA polymerase then binds to strands and splits the double helix
What happens during elongation of transcription?
-RNA polymerase moves down DNA molecule (strand being transcribed) in 3’-5’
-RNA polymerse then moves along the DNA strand, untwists the double helix and exposes the 10-20 nucleotides/time.
can there be more than 1 RNA polymerase to transcribe a gene at the same time?
yes, many RNA polymerase can transcribe a gene at the same time.
What does the RNA polymerase synthesize?
mRNA transcript
By having more than 1 RNA polymerase, what can they make mulitples of?
transcripts
How can the RNA polymerase add nucleotides?
Only add nucleotides to the 3’ end…(previous nucleotide)
what happens during the termination of transcription? What will the RNA polymerase reach?
-Termination sequence
what is the termination sequence in transcription?
an area where the transcript (like mRNA) undergoes modifications in the nucleus.
how does the transcript leave the nucleus?
through the nuclear pores
what happens to the gene expression after the termination of transcription?
gene expression continues with translation
what is the main purpose of translation in gene expression?
where the mRNA is read and translated into a string of amino acids, synthesizing proteins
what is the mRNA transcript used for in gene expression?
Language of mRNA is used to translate a polypeptide
where does translation in gene expression occur? (2)
in the rough ER or the cytosol
how many codons are there in translation?
64
how many codons are there in an amino acid?
20
if the number of codons in translation exceed the number of codons in amino acids, how does gene expression even work?
There are more corresponding codons for amino acids, so they actually have more than 20 and more than 64.
Is the genetic code important? If so, why?
The genetic code is redundant because it limits the impact of mutations. There are more than 1 codon for an amino acid meaning there are alot more combinations and diversity among a protein
How long is the transcript tRNA?
approx. 80 nucleotides
what does tRNA contain? What can this thing that it contains do?
-Anticodon (AAG, AAC, GCA)
It can base pair with the complemenatry codon of mRNA
At the other end of the tRNA molecule, there is a…
Binding site for specific amino acid to attach to ribosomes
What do the ribosomes do in translation in gene expression?
They synthesize polypeptides
How do ribosomes synthesize polypetides?
-they facilitate coupling of tRNA anticodons with mRNA codons to grow polypeptide chain
What subunits does the ribosome have?
-Large subunit
-small subunit
what are the subunits of ribosomes composed of? (2)
proteins and RNA (2/3 of mass)
Why do ribosomes take it’s shape and function the way it is?
Due to rRNA
What is the transcript rRNA?
Catalyst of peptide bond formation, acts as an enzyme
Why is the ribosome in 2 subunits, what is the main function of it’s shape being like that?
The function of the structure is to bring together the transcript mRNA and tRNA.
What does the large subunit of the ribosome contain? (hint: think monkey)
3 tRNA Binding sites
-Aminoacyl tRNA site (A site)
-Peptidyl tRNA site (P site)
-Exit site (E site)
APE!
If the RNA transcript is the coding strand, what is the RNA transcript complementary to?
It is complementary to the template strand
In transcription, where are the codons found?
Found on mRNA
What are the steps of translation?
-Initiation
-Elongation
-Termination
(different from transcription though)
What does the ribosome’s large subunit have to do with the steps of translation?
Initiation= P-site
Elongation= A-site
E-site,
Cycles until…
Termination
what happens at the p-site in initiation of translation? (3)
-small ribosomal subunits bind to mRNA scanning for start codon (AUG) the bind once found
-tRNA binds to mRNA at AUG (start codon) and transports anticodon (UAC, complementary) to start codon
-Large ribosomal subunit then binds with the help of GTP (energy)
what happens at the a-site in elongation of translation? (4)
-Anticodon of a-site base pairs with complemntary mRNA codon
-Hydrolysis of GTP increases accuracy & efficiency in step
-Translocation of a-site –> p-site & p-site –> e-site using GTP
-New cycle starts back at a-site
What happens at termination of translation?
-Elongation ends @ stop codon arrival (UAA, UAG, UGA)
-Release factor binds to A-site then dissasembles ribosome to stop translation
-Release factor also frees polypeptide
what is the release factor in translation?
Appears in termination of translation and it is a protein that binds to a-site, dissasembling the ribosome and freeing the polypetide, stopping translation.
After termination, what happens to the polypeptide in translation? (End of translation)
protein folds in cytoplasm or in LUMEN/membrane of the rough ER. The protein either stays in the cell, gets secreted, or gets incorporated into a membrane.
What is a mutation?
a change/changes in nucleotide sequence of an organism’s DNA or a virus’ DNA/RNA
what are mutations responsible for?
huge diversity of genes
why are mutations responsible for huge diversity of genes?
because mutations are the ultimate source of new genes
what are small-scale mutations?
Point mutations
what are point mutations?
changes in a single nucleotide pair of a gene
what happens if the point mutation occurs in cells that produce gametes?
mutation may be transmitted to offspring
what happens if the mutation has an adverse effect on phenotype of the organism?
Mutant condition may be reffered to as genetic disorder or hereditary disease
what happens if point mutation occurs in somatic cells?
It is Non-consequential **
-It can *result in dysfunctional cells or can be a *precursor to generation cancerous cells
What are the 5 point mutations?
-Base-pair substitution
-Silent mutation
-Missense mutation
-Nonsense mutation
-Insertion & deletion mutation
what is a base-pair substitution mutation?
Replacement of 1 nucleotide & it’s partner as well
What is a silent mutation?
Base pair substitution had zero effect of coded protein because of the redundancy of genetic code (ATA –> ATA still after we changed the base pair)
What is a missense mutation?
Base pair substitution that changes 1 amino acid to another
what happens to the protein after undergone a missense mutation?
-May have little effect on protein making it similar to the 1 it replaced.
-New amino acid may be in the same region where the exact sequence of amino acids are NOT essential to function
what is an example of a missense mutation?
Sickle-cell anemia
what is the evolution of sickle cell anemia?
-New amino acid has a different nucleotide
-sickle cell anemia was in a crucial region for folding and folded wrong, becoming non-functional/impart a new property
In this case, the sickle cell anemia’s subunit differs from the normal subunit where the oxygen capacity is reduced in sickle cell anemia