Lectures 5 and 6 Flashcards
What is the study of genetics?
Studies how physical traits and diseases pass form generation to generation
What are genes?
They are the physical units of heredity
They are the basic structural and functional unit of genetics
Genes are made up of DNA
Do we all have two copies of each gene?
Yes
One from each parent
Are most genes the same in all people?
Yes
<1% are slightly different between us
What is a gene physically?
It is a string of chemical building blocks or nucleotides in a DNA molecule
How many different nucleotides are there in DNA?
4
Each nucleotide is a letter
What do nucleotides do?
They store information in the form of a genetic code
What does a series of nucleotides form?
Amino acids
Chain of those make up polypeptides
What is an allele?
An allele is a gene
It was previously used to describe variant forms of a gene
An allele is one of a number of alternate forms of the same gene
What can different alleles result in?
Can result in different phenotypes, such as eye pigmentation
Most genetic variations result in little or no observable variation
What is a wild type allele?
It is a normal allele, as opposed to a mutant gene or allele
What is the scientific name for DNA?
Deoxyribonucleic acid
What is DNA?
It is the genetic code that determines all the characteristics of a living thing
What is DNA made of?
Nucleotides
What does each nucleotide comprise of?
A sugar, a phosphate molecule, and a base
How many genes does DNA contain?
Thousands
What is at the end of each chromosome?
Telomeres
They protect the ends of the chromosomes during DNA replication (plastic tip on shoelace)
What do telomeres consist of?
Repeats of DNA sequences associated with proteins
What happens to telomeres over time and many replications?
It becomes shorter and shorter
This is due to the fact that the DNA strand is unable to replicate itself to the very end
How do telomeres protect the chromosome?
The repetitive sequence of telomeres lacks information for protein synthesis, thus protects the genes that are in more internal regions of the chromosomes
What happens when the telomere gets too short?
The integrity of the genes is compromised and no longer divides
The condition or process of deterioration with age
May explain the functional decline of most body organs
What do chromosomes consist of?
Single long molecule of double stranded DNA
Typically in homologous pairs
One maternal and one paternal
How many pairs of chromosomes do humans have?
23
How are chromosomes made?
A single length of DNA is wrapped many times around lots of proteins called histones, to form structures called nucleosomes
These nucleosomes then coil up tightly to create chromatin loops
The chromatin loops are then wrapped around each other to make a full chromosome
What is the short arm of a chromsome?
p
What is the long arm of a chromosome?
q
What is holding both sides together?
Centromere
What are histones?
Proteins
What are chromatin loops similar to?
Thread
And the chromosome is the yarn
What is a genotype?
Genetic makeup of an organism
The sum of genes transmitted from parent to offspring
What is a phenotype?
Manifestation of genes
Anatomical and behavioral traits from both heredity and the environment
What you can see
What is a karyotype?
The entire set of 46 chromosomes
Looks at all of the chromosomes and any abnormality with them
What are proteins a product of?
Genes
DNA controls the kind of and amounts of proteins present in cells
Phenotypes are controlled by proteins
Does each gene code for multiple proteins?
Yes
Humans contain about 20,000 to 25,000 genes that specify between 100,000 and 200,000 proteins
What are proteins made of?
Amino acids
How many essential amino acids are there?
20
10 made in our bodies and 10 we need in our diet
Each amino acid has what? (3)
Animo group
Carboxyl group
R group
What is the R group of an amino acid?
It is a term used to indicate the position of an unspecified group in a chemical structure
Side chains that are different for each amino acid
What is special about Tyrosine (amino acid)?
Only produced by phenylalanine (produced outside the body)
You need to consume phenylalanine to produce Tyrosine
How are amino acids linked together?
Covalent peptide bonds
Formed between the amino group and the carboxyl group
What do two linked amino acids form?
A dipeptide
What do three amino acids form?
A tripeptide
What do 10 or more amino acids form?
A polypeptide
What happens when the carboxyl group bonds with the amino group to form a polypeptide?
It releases a molecule of water
Why are covalent bonds used for polypeptides?
Because they are very strong
They keep the electrons stable
How is the sequence of amino acids determined for a protein?
Determined by the bases in the gene encoding that protein
Proteins contain within their amino acid sequences the necessary information to determine what?
How that protein will fold into a three-dimensional structure
The stability of the resulting structure
What happens if the code is read incorrectly?
The protein will be wrong
It won’t do what it was supposed to do
Is DNA the hereditary transmission molecule in gametes?
Yes
What are the two primary functions of DNA?
To duplicate itself
To control the development of the rest of the cell in a specific manner
What is a nucleotide?
Single building block of DNA
Consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base
What are the bases in DNA?
Adenine
Guanine
Cytosine
Thymine
What bases pair together in DNA?
A and T
C and G
Which bases are purines (two ring structure)?
A and G
Which bases are pyrimidines (one ring structure)?
C and T
What are pentoses?
The sugar in nucleic acids, contain 5 carbon atoms
What is the sugar called in DNA?
Deoxyribose
What is the sugar called in RNA?
Ribose
What is the difference between deoxyribose and ribose?
A single oxygen atom that is absent (deoxy) in deoxyribose but present in ribose
What is present at the 5’ position?
A phosphate molecule
What is present at the 1’ position?
One of the 4 bases
What are chains of nucleotides called?
Polynucleotides
In a polynucleotide, are there different structures at each end?
Yes
At one end (5’), is a phosphate group
At the other (3’), there is sugar molecule
Are nucleotides written starting with the 5’ end or the 3’ end?
5’
Does each DNA strand run in opposite directions?
Yes
One is a 5’ and the other is a 3’
What makes up the DNA chain backbone?
The link of sugar and phosphate
The bases are in the middle of the DNA
What is a histone?
It is a core
The DNA is wound around it
What is a nucleosome?
The complex unit of DNA and histones
What is a genome?
A complete DNA sequence of an organism with its complete genetic information
What can result in an altered phenotype?
Any change in order or number of the bases in a gene
What is great about the double helical structure of DNA?
Protects DNA against loss and damage
Provides a means of coding and storing vast amounts of info
Provides a mechanism for replication
Which strand is the leading strand?
The 5’
Can only be coded in the 5’ to 3’ direction
The 5’ end of the strand is the promoter
What is the other strand (3’) called? And what does it do?
The antisense or lagging strand
Carries info necessary to make proteins by binding to a corresponding mRNA
What is RNA made up of?
Nucleotides
Phosphate, sugar, and base
What does RNA do?
It is vital for coding, regulation, and expression of genes
Are all of the bases the same in RNA as DNA?
No
All the same except Uracil (U) replaces Thymine
Where is DNA found in the cell?
Nucleus and mitochondria
Where is RNA found in the cell?
Cytoplasm in association with ribosomes
What are ribosomes?
They are large protein synthesis factories that form protein through the process of translation in the cell cytoplasm
Is RNA single stranded or double stranded?
Single
Does RNA carry protein-decoding information?
Yes
What are the three different classes of RNA?
mRNA, rRNA, and tRNA
Where is mRNA found?
Nucleus
How many nucleotides make up a codon?
3
What do codons do?
They specify an amino acid
Why are there extra codon combinations?
Redundancy
What two amino acids only have one codon?
Methionine and tryptophan
How many stop codons are there?
Three
They cease translation
What are the stop codons?
UAA
UAG
UGA
What is the start codon?
AUG
methionine
What is the flow of hereditary info?
DNA to RNA to protein
Does DNA directly code for proteins?
No
DNA directs gene expression by the transcription of DNA to RNA and the translation of mRNA to protein
What is transcription?
The information encoded in a gene is copied into the mRNA
Exact copy of DNA
What is translation?
Nucleotide sequence of the mRNA is converted to an amino acid sequence of a protein
Where does mRNA move?
From the nucleus to the cytoplasm
Translation happens in the cytoplasm
Which strand of DNA is the template of transcription?
Template strand
How does transcription begin?
When helicase (enzyme) unwinds the double helix
Which enzyme initiates transcription?
RNA polymerase
What is the complimentary partner of the template strand?
The coding strand
Is the RNA transcript identical to the DNA coding strand?
Yes, except for Uracil replacing Thymine
What are the three stages of transcription?
Initiation
Elongation
Termination
What happens during the initiation stage?
RNA polymerase binds to the promoter region, helicase unzips and exposes the 3’ end for a template strand for RNA synthesis
What happens during elongation?
The RNA polymerase links the RNA nucleotides to form an RNA molecule
What happens during the termination stage?
Terminator sequence at the end of the gene causes RNA polymerase to detach from the DNA strand, the mRNA is released, DNA reforms double helix form
What are exons?
Regions in the DNA that contain the coding information that will be used during translation
Present in mature RNA
What are introns?
Non-gene regions of DNA
Spliced out from pre-mRNA before RNA is translated into proteins
Essential for normal gene function
What happens after introns are spliced out from pre-RNA?
Mature RNA forms
Where does translation occur?
In the ribosomes in the cytoplasm
How are the amino acids bound together?
Covalent bonds called peptide bonds
What is the result of translation?
A string of amino acids called polypeptides
What are the two functions of AUG?
It is a start codon, marking the beginning of a coding sequence
It also encodes methionine (if used later in the chain)
Translation between languages requires an interpreter. Who is the interpreter?
tRNA
Transfer RNA
What does tRNA look like?
Single strand of nucleotide bases
Folds up on itself so that some parts are actually double stranded
Looks like a 4 leaf clover
What does tRNA do?
Match the codons in mRNA with the proper amino acids for incorporation into a protein
Recognize the proper codon in mRNA
Can tRNA recognize and bind amino acids itself?
No
It needs help from an enzyme, Aminoacyl tRNA Synthetase
Binds the correct amino acid to tRNA which is then carried to the ribosome
At one end of the tRNA is a sequence of three nucleotides called what?
The anticodon
Recognizes and pairs with a specific complimentary codon in the mRNA
Acts as an organizer
Is an anticodon a perfect complementary match to a codon?
Yes
AGC (codon) will be UCG (anticodon)
Will the same tRNA that contains the anticodon also carry the amino acid?
Yes
Does translation also have three stages?
Yes
Initiation, elongation, and termination
What are antibiotics?
Chemicals produced by micro-organisms as defense mechanisms against other microbes
Fight bacterial infections
Can steps of protein synthesis be inhibited by antibiotics?
Yes
What does tetracycline interfere with?
Initiation of translation
What does streptomycin interfere with?
Effects efficiency of protein synthesis by changing how mRNA codons interact with tRNA anticodons
What does erythromycin interfere with?
Inhibits the movement of ribosomes along mRNA
Do we have natural protections against gene mutation?
Yes
Mutations are corrected by using the undamaged DNA strand as the template strand to correct the damaged one
Redundancy of the genetic code is also a protector
What happens if both of the strands are damaged or damage happens just prior or during DNA replication?
Results in permanent alteration of the DNA sequence
What is one naturally occurring proofreading enzyme that we have?
DNA polymerase
What can an enzyme do if an incorrect nucleotide is inserted?
Detect the mistake
Move backwards until the incorrect nucleotide is eliminated
Insert the correct nucleotide
Proceed with replication
What happens if a mistake is not caught by the enzyme?
It is a spontaneous mutation
What are some different types of mutations?
Translocation
Duplication
Deletion
Gene duplication or deletion
What is translocation?
A chromosomal segment transferred to another, nonhomologous chromosome
What is duplication?
A chromosome segment is repeated
More than one copy is present within the chromosome
Results in trisomy 21
What is deletion?
A segment of the chromosome is missing
What is gene duplication or deletion?
Unequal crossing over in meiosis 1
One daughter cell receives an extra chromosome, and the other receives one less chromosome
What is point mutation?
The replacement of a single base nucleotide with another base nucleotide
Either DNA or RNA
Can include insertions or deletions of a single base pair (extra base or missing base)
What are the two categories of point mutations?
Transition and transversion
What is transition?
Replacement of a purine base with another purine base (adenine instead of guanine)
Replacement of a pyrimidine base with another pyrimidine (thiamine instead of cytosine)
What is transversion?
A single (two ring) purine (A or G) is changed for a (one ring) pyrimidine (T or C), or vice versa
Can point mutations include nonsense mutations?
Yes
Codes for a stop codon prematurely
Stops protein translation
Phenotypic changes can occur
Can point mutations cause silent mutations?
Yes
Codes for the same amino acid
No phenotypic change
UUU or UUC = phenylalanine
No mutation
Can point mutations cause missense mutations?
Yes
Codes for a different amino acid
What are the two types of missense mutations?
Conservative and non-conservative
What is a conservative missense mutation?
No phenotypic effect if the substituted amino acid was similar to the original
What is a non-conservative missense mutation?
Can result in a nonfunctional protein
For e.g., sickle-cell disease is caused by a single point mutation in the hemoglobin gene that converts a GAG codon into GUG, which encodes Valine rather than Glutamic acid
It could be conditional lethal
What is a frameshift mutation?
Insertions or deletions of a single (or more) base pair
This type of mutation can make the DNA meaningless and often results in a shortened protein
Frameshift mutation is the equivalent of adding or removing letters in a sentence
For example, ‘t’ from cat is removed but the original letter spacing remains the same
Original: The fat cat ate the wee rat*
Frameshift: The fat caa tet hew eer at
Will be nonsense
What is epigenetics?
The study of how behaviors and environment can cause changes that affect the way genes work, i.e., change the expression of genes
Are epigenetic changes reversible?
Yes
They do not change the underlying DNA sequence
Phenotype change, not genotype
What influences epigenetics?
Environmental and lifestyle factors that may influence epigenetic mechanisms include, DNA methylation, histone modifications, and microRNA expression
What types of illnesses are linked to epigenetics?
Most cancers, cognitive dysfunction, autoimmune, and neurobehavioral illnesses such as schizophrenia
Is transgenerational trauma believe to be caused by epigenetics?
Yes
Can leave a chemical mark on genes that is passed down
