Unit 4: DNA Flashcards
What does DNA stand for?
Deoxyribonucleic Acid
Does anyone have the exact same DNA?
No two people have the exact same DNA unless they are identical twins
What is DNA fingerprinting also known as?
DNA profiling, in which it is a technique that helps scientists distinguish between individuals of the same species using only samples of their DNA
The process of DNA fingerprinting was invented by?
Alec Jeffreys at the University of Leicester in 1985
What can DNA fingerprinting be used for?
- Identify the bodies of victims
- Paternity
- Identify victims of war and large-scale disasters
- Track genetically modified crops
- Settle immigration disputes
Small amount of biological evidence left at crime scenes is called…
Trace evidence
What are some examples of biological evidence?
Saliva, blood, skin
What type of evidence is DNA evidence?
Because it identifies a specific person, it is considered individual evidence
What does it mean when the DNA fingerprint comes up as no match?
It is a very powerful argument for excluding an individual
Ambiguous or no result
This means that there is no result because there were problems with the specimen or the test
Match
The crime scenes DNA and the suspect DNA are the same but it is the function of the lab, expert witnesses, and the courts to determine guilt
What type of acid is DNA?
Nucleic Acid and it is found in the nucleus of your cells
How many pairs of chromosomes do human cells have?
23 pairs
How many total chromosomes do humans have?
46
How many chromosomes are in sperm and egg cells
23 because they are not in pairs
What are genes?
Each chromosome pair can be broken into smaller segments; genes control the traits of the organism, and therefore can vary between individuals
DNA has how many nitrogenous bases…
4
What are the 4 nitrogenous bases?
- Adenine (A)
- Thymine (T)
- Guanine (G)
- Cytosine (C)
These bases form according to the base pairing rule which is…
- Adenine binds with only THYMINE
- Cytosine binds with GUANINE
These pairs are considered to be complementary
i. if one strand of DNA has the genetic code: ATCTGC
TAGACG - its complementary strand would read
What shape is DNA strand?
DNA is made when two strands twist together in a shape called the double helix
What are the sides of the helix called?
It is referred to as the backbone of DNA which is made up of alternating sugar (the sugar is called deoxyribose) and phosphate molecules
What are the rungs of the helix made up of?
They are made up of the paired nitrogenous bases (A-T, C-G) which help to code the DNA with instructions for the cell
What is DNA in Chromosomes called?
Nuclear DNA
Is nuclear DNA from both the mother and father?
True and it is identical in all cells of an individuals body
Is mitochondrial DNA linear or in the form of a circular loop?
In a circular loop and it is only inherited from their mother
What is the human genome?
Is the total amount of DNA in a cell. It is contained in both the nucleus and mitochondria
How many base pairs does the human genome have?
3 billion base pairs
What is the purpose of the genome?
Is to code the blueprint for the human body and how it works, it is responsible for telling the body to make proteins and other needed molecules
What are exons?
Exons are encoded DNA with directions to build molecules
What are introns?
They are un-encoded DNA, that do not code for the production of molecules and are make up most of DNA and are known as junk DNA and they are important in gene splicing and have an important role in biology
Are most of the human genome the same in all individuals?
Yes it is the same, but some variation exists among individuals
Where is most of the variation in DNA found?
In the non-coding DNA or introns and much of the non-coding DNA is in the form of repeated base sequences and some of these sequences can be repeated many times
What type of charge does DNA have?
Slightly negative
What are Polymorphisms?
They are non-coded DNA segments that have unique patterns of repeated base sequences that are unique to individuals
What are Variable Numbers of Tandem Repeats?
VNTR are 9 to 80 bases in length
What are Short Tandem Repeats?
STRs are 2 to 5 bases in length
What are SNP’s?
Single Nucleotide Polymorphisms like T, A
VNTR and STR data from DNA fingerprints can be analyzed for two main purposes….
i. tissue matching (comparing DNA evidence from a crime scene with DNA from a suspect, and how it looks two samples that have the same band pattern are from the same person)
ii. inheritance matching (comparing family member’s DNA for proof of familial relationships and how it looks each band in a child fingerprint must be present in at least one parent 50% from mom and 50% from dad)
What is Trace Evidence?
- Is the small amount of evidence left at a crime scene is very small and therefore considered to be trace evidence
- A problem with analyzing trace evidence is that forensic tests will destroy the evidence sample, as in the case with DNA
- Therefore, prior to DNA fingerprinting, PCR us used
What is used to prevent DNA evidence from being destroyed and to replicate DNA samples?
PCR which is Polymerase Chain Reaction; PCR is a technique that makes thousand of copies of segments of DNA that investigators want to analyze
How does PCR work?
Crime scene (template) DNA is mixed with nucleotides, an enzyme known as DNA polymerase, and primase
Primers are short segments of complementary DNA that base-pair with the template DNA upstream of the region of interest and serve as recruitment sites for the polymerase
Cycles of denaturation, annealing, and extension are repeated to achieve exponential amplification of the target sequence, allowing for billions of DNA copies to be produced in just a few hours
To avoid DNA evidence contamination, crime scene investigators should…
- Wear disposable gloves and change them often
- Use disposable instruments for handling each sample
- Avoid talking, coughing, or sneezing over evidence
- Do not touch your face or body when collecting or packaging evidence
- Air-dry evidence before packaging. If evidence cannot be dried, it may be frozen
- Avoid using plastic bags to store evidence that contains DNA; use paper bags or envelopes
- Keep evidence cool and dry during transportation and storage. Avoid direct sunlight which can damage DNA
Steps of DNA Fingerprinting
Step 1: Extraction of the DNA
Step 2: Cut the DNA into restriction fragments RFLP’s, Restriction Fragment Length Polymorphisms
Step 3: Amplification (making many copies of those fragments) use PCR
Step 4: Electrophoresis (a process that separates RFLPs, according to their length, creating a DNA fingerprint)
How does Gel Electrophoresis Work?
- Restriction enzymes cleave DNA into smaller segments of various sizes
- DNA segments are loaded into wells in a porous gel. The gel floats in a buffer solution within a chamber between two electrodes
- When an electric current is passed through the chamber, DNA fragments move toward the positively-charged cathode
- Smaller DNA segments move faster and farther than larger DNA segments
Analysis of DNA Fingerprints
DNA fingerprints should look like a striped column. In order for DNA fingerprints to match, the columns must have bands in the exact same places with the exact same widths
What does DNA Fingerprinting help with?
- Match a crime scene DNA with a suspect
- Eliminate a suspect
- Free a falsely imprisoned individual
- Determine maternity, paternity, or match to another relative
- Identify human remains
What is the point of DNA?
DNA contains genetic codes that determine proteins that make up our physical features
What are Purines?
They are double ring structures (adenine and guanine are purines)
What are Pyrimidines?
They are single ring structures (thymine and cytosine are pyrimidines)
Do purines always bond with pyrimidines?
YES
What is Chargaff’s Rule?
It states that DNA from any cell should have a 1:1 ratio of pyrimidine and purine bases (as per the base pairing rules)
- In other words, the amount of guanine is equal to cytosine; and the amount of adenine is equal to thymine
ex: if a DNA molecule contains 28% cytosine, we can figure out how much guanine, thymine, and adenine are present in the molecule
Cytosine (28%)
Guanine (28%)
Adenine (22%)
Thymine (22%)
Who are Watson and Crick?
They determined the shape of DNA based on X-ray diffraction their work was more of a puzzle completion, they figured out that the shape of DNA was a double helix (2 strands of nucleotides and helix is twisted)
Who was Rosalind Franklin?
She put work and information in to determine the structure of DNA
What is Photo 51?
It was Rosalind Franklin’s work that confirmed the helical structure of DNA
How do the bases bond together?
Using hydrogen bonds
How many hydrogen bonds do adenine and thymine have?
2 bonds
How many hydrogen bonds do guanine and cystosine have?
3 bonds
Are hydrogen bonds the weakest type of bond?
True
When does DNA replication occur?
During the synthesis phase of the cell cycle which is before the cell divides
DNA Replication the First Step…
The first step is to break those hydrogen bonds between the bases an enzyme called DNA helicase breaks the hydrogen bonds and unzips the original parent DNA molecule
What does the enzyme DNA Helicase do?
It breaks the hydrogen bonds and unzips the original parent DNA molecule
DNA Replication Step 2…
Once the DNA strands are unzipped, the nucleotides are exposed
The second step involves another enzyme called DNA Polymerase this enzyme reads the DNA and determines which NEW nucleotides to add to the parent strand
What is DNA Polymerase?
This enzyme reads the DNA and determines which new nucleotides to add to the parent strand
What are Replication Forks?
They form at multiple points in the DNA to speed up replication
What do two replication forks make?
Replication bubbles
What do 5’ and 3’ mean?
Since DNA is a 3-dimensional molecule made of linked nucleotides, it really doesn’t have a “left” or “right”; “up” or “down”. If we have ti refer to DNA’s direction we use 5’ and 3’ (5 prime and 3 prime). Recall that deoxyribose is a 5 carbon sugar. These numbers (5,3) are in respect to the position of the 5-carbon sugar
What does it mean when DNA is Antiparallel?
DNA molecules are antiparallel- meaning the two strands run parallel to one another but in different directions (it always looks like one strand is up-side-down relative to the other)
And during DNA replication, DNA polymerase reads the parent molecule in the 3’ and 5’ direction (opposite)
How to remember… when you read a book you would read chapters 3-5
What is the Leading Strand?
One new strand will move continuously TOWARD the replication fork
What is the Lagging Strand?
Because the strands are anti-parallel, the other strand will move AWAY from the replication fork
What are Okazaki fragments?
They are short segments of new DNA on the lagging strand
How many strands are on the final product of DNA Replication?
Two molecules of DNA (4 strands total since each molecule is double stranded)
Is DNA semi-conservative?
True meaning each time DNA is copied, the original DNA molecule is saved, each new molecule consists of one parental strand, and one (new) daughter strand
Why is DNA important?
DNA is important because it has the recipe for making proteins
What is RNA?
Ribonucleic Acid is the copy of DNA code; think of DNA as library it contains very important books, but no checking them out! However, copies can be made and those can leave the library, the copies are like the RNA. It is a nucleic acid and is made of linked nucleotides (like DNA)
What are the differences between DNA and RNA?
- DNA is double-stranded and RNA is single-stranded, this means that RNA is smaller than DNA
- RNA contains 4 nitrogen bases adenine, guanine, cytosine, and uracil thymine is not present in RNA
- RNA contains the 5-carbon sugar ribose which has more more oxygen atom than deoxyribose whereas DNA has deoxyribose
What is Messenger RNA?
Messenger RNA (mRNA) is complementary to the original strand of DNA. mRNA is first created in the nucleus and then travels to the ribosomes in the cytoplasm. mRNA uses the DNA’s code (or message) to make proteins
What are Proteins made up of?
Amino acids
What are codons?
Individual DNA codes the codons correspond to specific amino acids
What do codons consist of?
They consist of groups of 3 nucleotides called triplets, and each codon codes for one amino acid this is where we need RNA’s help
mRNA is always complementary to the template DNA strand
True
What are the mRNA codons?
- UGC (cysteine)
- AAU (asparagine)
- CGG (arginine)
How many amino acids are there?
Though there are only 20 different amino acids, they are sequenced differently and come in different shapes to make for thousands of different proteins
The process of protein synthesis
It is a 2 part process in which DNA is decoded into corresponding proteins
- The first process is known as transcription (mRNA is created by transcribing the DNA’s code)
- The second process is translation (the mRNA that was manufactured during transcription is translated into an amino acid sequence (proteins)
- Occurs in the nucleus and cytoplasm
What are the three types of RNA?
- mRNA
- tRNA (transfer RNA helps transfer amino acids to the corresponding mRNA codons, tRNA is always complementary to the mRNA strand, they are also referred to as “anti-codons” because they are complimentary to mRNA codons)
- rRNA (a major component of ribosomes; also helps bond amino acids together to make polypeptides (proteins)
What are proteins made of?
amino acids
What are some start codons?
AUG codes for the amino acid methionine
What are some stop codons?
UAA, UAG, UGA
Where is DNA located in the cell?
Nucleus
DNA is made up of individual units called…
Nucleotides
Purines only bond with pyrimidines and vice versa
True
DNA’s shape is described as a…
double helix
What does DNA do?
DNA contains genetic codes that determine proteins that make up our physical features
What is the relationship between DNA and amino acids?
Amino acids are the building block of proteins. A gene’s DNA sequence determines the order of amino acids that make up a protein, so if there are changes in the DNA sequences there would be a change in the amino acid sequence as well
What is DNA coiled into?
Chromosomes
Proteins called _____ and _____ help to keep the DNA ____
Nucleosomes and histones; coiled
What is genetic genealogy?
It is the combination of genetic analysis with traditional historical and genealogical research to study family history
What is genealogy used for?
For forensic investigations, it can be used to identify remain by tying the DNA to the family of a missing person
Or to point to the likely identity of a perpetrator
- By comparing a DNA sample to a database of DNA from volunteer participants, it is possible to determine whether there are relatives of the DNA sample in the database and how closely related they are
- This information can then be cross-referenced with other data sources used in traditional genealogical research, such as census records, vital records, obituaries and newspaper activities
What does genetic genealogy use to identify DNA?
It uses autosomal DNA single nucleotide polymorphisms (SNP’s) to determine how closely related 2 individuals are
Unlike other genetic markers such as mitochondrial DNA or Y chromosome DNA, they must make sure that DNA is inherited from all ancestral lines and passed on by both males and females and thus can be used to compare 2 individuals regardless of how they are related
Who was Joseph James DeAngelo aka the Golden State Killer
- He was an American serial killer, serial rapist, burglar and former police officer who committed at least 13 murders, 51 rapes, and 120 burglaries across California between 1974 and 1986
What were his nicknames?
-burglary: Visalia ransacker
- sexual assaults: east area rapist
- murders: the original nightstalker
- the golden state killer
Who was Michelle McNamara?
To heighten the awareness of the case, the writer coined the name golden state killer in early 2013
What happened in James’ early life that could have led to his behaviour?
- Saw his younger sister raped
- Was abused by his father
- He committed burglaries and animal torture as a teen
How did Deangelo get caught?
- They uploaded the killers DNA profile from a rape kit to the genealogy website GEDmatch
- The website identified 10-20 people who had the same great great great grandparents as the Golden State Killer; and they used this list to create a family tree from this tree they got 2 suspects one ruled out by a DNA test leaving DeAngelo the main suspect
- DNA was collected from the door handle of his car and both samples match the Golden State crimes
What is DNA Phenotyping?
It is the prediction of physical appearance from DNA (think photograph what do you see physical features)
- It can be used to generate leads in cases where there are no suspects or database hits, to narrow suspect lists, and to help solve human remains cases
- DNA carries the genetic instructions for an individual’s characteristics, producing a wide range of appearances among people
- Snapshot reads tens of thousands of genetic variants (genotypes) from a DNA sample and uses this info to predict what an unknown person looks like
- It predicts genetic ancestry, eye colour, hair colour, etc
Can you figure out age, BMI and facial hair with genetic phenotyping?
False
What is touch DNA/trace DNA?
- It is a forensic method for analyzing DNA left at the scene of a crime
- It is called “touch DNA” because it only requires very small samples, for example from the skin cells left on an object after it has been touched or handled, or from footprints
- Touch DNA analysis only requires seven or eight cells from a layer of skin
- This technique has been criticized for high rates of false positives due to contamination
When is Touch DNA or Trace DNA used mostly?
To eliminate suspects rather than prosecution because of the high chance of contamination
