PLTW: Unit 1.1 Exam Review

A set of 35 flashcards covering key concepts, processes, and definitions related to crime scene investigation, blood analysis, and DNA structure and analysis.

A crime scene sketch must include a comprehensive key detailing all pieces of evidence with corresponding labels, a comprehensive legend specifying crucial environmental and temporal data (such as the precise date, time, and location of the scene, along with the ambient temperature), and an accurate scale to represent real-world distances and proportions, ensuring the sketch is a true representation of the scene.

What key details are essential for a crime scene sketch?

Upon arrival, a crime scene investigator must first examine the scene and meticulously mark all evidence. This is followed by sketching the crime scene to document spatial relationships, taking detailed photographs and comprehensive notes, and finally, carefully collecting all evidence to preserve its integrity for analysis.

What are the initial actions for a crime scene investigator at a scene?

The role of baseline questions in a polygraph test is to establish a control group by recording an individual's normal, truthful physiological responses to neutral questions. These established responses serve as a reference against which reactions to relevant questions can be compared to detect deviations indicative of deception.

What is the primary purpose of baseline questions in a polygraph test?

A polygraph test typically monitors several involuntary bodily functions: respiration rate (breathing patterns), heart rate (pulse), skin conductivity (indicating sweat gland activity), blood pressure, and sometimes body temperature. Changes in these indicators can suggest emotional arousal linked to deception.

Which physiological indicators are monitored by a polygraph test?

When an individual is being deceptive during a polygraph, their heart rate invariably increases due to stress. Their respiration rate also tends to increase, often becoming shallower or more irregular; however, some individuals might attempt to control their breathing, which can manifest as abnormally slow or held breaths, complicating interpretation.

How do heart rate and breathing typically change when someone is lying?

The three major structural components of a human hair shaft are the outer protective cuticle (made of overlapping scales), the central and thickest cortex (containing pigment and providing strength), and the innermost medulla (a core that can be continuous, interrupted, fragmented, or absent).

What are the three main structural components of hair?

Minutiae are the unique, small ridge characteristics and patterns found within fingerprints, such as bifurcations (where a ridge splits), ridge endings, enclosures, and short ridges. These distinct details vary highly from person to person and are the fundamental features used to compare and match fingerprints for identification.

What are minutiae in the context of fingerprint analysis?

For a forensic technician to conclusively confirm a fingerprint match, the widely accepted standard dictates matching approximately 12\text{-}15 corresponding minutiae (unique ridge details) between a latent print from a crime scene and a known reference print. This number can vary depending on jurisdiction and the quality of the print.

How many minutiae matches are generally required to confirm a fingerprint?

Digital evidence can include a wide range of electronic data such as electronic photos, text messages, data from social media applications, emails, voicemail recordings, location tracking information from mobile devices or GPS, and internet browser history. Any data generated, stored, or transmitted digitally can potentially serve as forensic evidence.

What are common examples of digital evidence in forensic investigations?

The four main components constituting human blood are: Red blood cells (erythrocytes), which transport oxygen; White blood cells (leukocytes), crucial for the immune system; Platelets (thrombocytes), essential for clotting; and Plasma, the liquid matrix that suspends all cellular components and transports various dissolved substances.

What are the four primary components that make up human blood?

The principal function of red blood cells (erythrocytes) is to efficiently transport oxygen from the lungs to all tissues and organs throughout the body, facilitated by the hemoglobin protein they contain, and to carry carbon dioxide back to the lungs.

What is the main function of red blood cells?

A presumptive blood test is a rapid, preliminary chemical test used to indicate the possible presence of blood in a sample at a crime scene or in a laboratory. It provides an initial 'presumptive positive' result, suggesting blood is likely present, but does not confirm it definitively or identify its species of origin.

What is the purpose of a presumptive blood test?

In class, the Kastle-Meyer test was used as a common presumptive test for blood analysis. This chemical test reacts with the hemoglobin in blood to produce a characteristic pink color, providing a preliminary indication of blood's presence.

Which common presumptive test for blood was used in class?

The key difference is that a presumptive blood test is an initial screening that suggests the likely presence of blood (e.g., through a color change), while a confirmatory blood test provides a definitive identification of blood and can further analyze specific characteristics, such as distinguishing human blood from animal blood or determining blood type.

How do presumptive and confirmatory blood tests differ?

Individuals with blood type A possess A antigens on the surface of their red blood cells. In their blood plasma, they naturally have B antibodies, which would react adversely if they encountered B antigens from another blood type.

What antigens and antibodies are found in blood type A?

Individuals with blood type B can safely receive blood transfusions from donors who are either blood type B (due to sharing the same antigens) or blood type O (because O blood lacks A and B antigens, making it a universal donor). They cannot receive blood from types A or AB.

From whom can individuals with blood type B safely receive blood?

The crucial function of platelets (thrombocytes) in the blood is to facilitate blood clotting (coagulation). When a blood vessel is injured, platelets rapidly aggregate at the site, forming a plug and releasing factors that initiate the cascade leading to the formation of a fibrin clot, which seals the wound and prevents excessive blood loss.

What is the primary function of platelets in the blood?

The significance of DNA's structure lies in the precise linear sequence of its nitrogenous bases (Adenine, Thymine, Guanine, Cytosine). This specific arrangement of bases forms the genetic code, which dictates the production of specific proteins and, consequently, determines all the unique traits and characteristics expressed in an organism, from its physical appearance to its physiological functions.

Why is the structure of DNA fundamentally important?

The fundamental building block, or monomer, that polymerizes to form the long chain molecule of DNA is the nucleotide.

What is the basic monomer unit that makes up DNA?

Each nucleotide in DNA is composed of three covalently linked molecules: a nitrogenous base (which can be Adenine, Thymine, Cytosine, or Guanine), a phosphate group, and a 5-carbon sugar called deoxyribose.

Identify the three molecular components that form a nucleotide.

The two complementary strands of the DNA double helix are securely held together by relatively weak, non-covalent hydrogen bonds. These bonds form specifically between the paired nitrogenous bases across the helix (Adenine with Thymine, and Cytosine with Guanine).

Which type of chemical bond holds the two strands of DNA together?

There are specifically two hydrogen bonds formed between the complementary nitrogenous bases Adenine (A) and Thymine (T) when they pair in the DNA double helix, contributing to the molecule's stability.

How many hydrogen bonds form between Adenine (A) and Thymine (T) in DNA?

There are specifically three hydrogen bonds formed between the complementary nitrogenous bases Cytosine (C) and Guanine (G) when they pair in the DNA double helix, making this base pair slightly stronger and requiring more energy to separate compared to an A-T pair.

How many hydrogen bonds form between Cytosine (C) and Guanine (G) in DNA?

The importance of DNA strands being held by relatively weak hydrogen bonds lies in its crucial biological advantage: these bonds allow the two helices to easily separate, or 'unzip,' without requiring excessive energy. This temporary separation is essential for processes like DNA replication (making copies) and transcription (creating RNA templates for protein synthesis), where the individual strands must be accessed and 'read'.

What is the biological advantage of weak bonds holding DNA strands together?

Chargaff's Rule, a fundamental principle of molecular biology, states that in any double-stranded DNA molecule, the total molar quantity of adenine (A) is always approximately equal to the amount of thymine (T), and similarly, the total amount of cytosine (C) is approximately equal to the amount of guanine (G). This reflects the precise base-pairing rules within the DNA helix.

Explain Chargaff's Rule regarding DNA base composition.

A purine (a larger, double-ring nitrogenous base like Adenine or Guanine) must always pair with a pyrimidine (a smaller, single-ring nitrogenous base like Cytosine or Thymine) in the DNA double helix. This specific pairing is critical to maintain a consistent and uniform width (diameter) of the DNA molecule along its entire length, ensuring its stable double helix structure and function.

Why is strict purine-pyrimidine pairing essential in DNA?

Following the specific base-pairing rules (Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C)), the complementary DNA strand for the given sequence ATGTTCGATC would be TACAAGCTAG.

Determine the complementary DNA strand for ATGTTCGATC.

A restriction enzyme is a specialized protein, primarily found in bacteria, that functions as a molecular scissor. It is capable of recognizing and precisely cutting double-stranded DNA molecules at highly specific, predetermined nucleotide sequences known as restriction sites.

What is a restriction enzyme?

The key variation among different types of restriction enzymes lies in the specific nucleotide sequences they recognize and cleave within a DNA molecule. Each unique restriction enzyme binds to and cuts DNA only at its own distinct recognition site, which is typically a short, palindromic sequence of bases.

How do different restriction enzymes vary?

The typical sequential steps for analyzing DNA, particularly in forensic contexts, include: 1. DNA extraction and purification, to isolate and clean the DNA sample; 2. PCR (Polymerase Chain Reaction), to amplify specific regions of DNA; 3. Restriction digest, where restriction enzymes cut the DNA into fragments; and 4. Gel electrophoresis, to separate and visualize these fragments based on size.

What is the correct order of steps for analyzing DNA evidence?

Each cycle of the Polymerase Chain Reaction (PCR), a technique used to amplify DNA, consists of three temperature-dependent stages: 1. Denaturation, where the DNA strands separate; 2. Annealing, where primers bind to the single-stranded DNA templates; and 3. Elongation (or extension), where new DNA strands are synthesized by DNA polymerase.

What are the three main stages of a PCR cycle?

The denaturation step in the Polymerase Chain Reaction (PCR) requires a high temperature, typically ranging from 94 to 98 degrees Celsius (94\text{-}98°C). This heat is crucial for breaking the hydrogen bonds between the two strands of the DNA double helix, thereby separating them into single-stranded templates for replication.

What temperature range is used for the denaturation step in PCR?

The principal purpose of gel electrophoresis is to separate macromolecules, particularly DNA fragments or proteins, based primarily on their size and electrical charge. When an electric current is applied, these charged molecules migrate through a porous gel matrix, with smaller fragments moving faster and further than larger ones, allowing for their separation and analysis.

What is the primary function of gel electrophoresis?

Analyzing Restriction Fragment Length Polymorphisms (RFLPs) using gel electrophoresis is crucial because these variations in DNA fragment lengths, produced by restriction enzymes, generate a unique banding pattern known as a DNA profile. This profile is essential for comparison and identification purposes in forensic science, enabling investigators to match evidence DNA to suspects or victims with high scientific certainty.

Why is it important to analyze RFLPs using gel electrophoresis?

Forensic analysis of digital evidence can reveal vital investigative information, including potential links between suspects (e.g., communication records, shared files), help establish accurate timelines of events (e.g., access logs, message timestamps), and pinpoint specific geographical locations connected to the crime (e.g., GPS data, Wi-Fi connections). This information helps reconstruct crime scenarios and build legal cases.

What types of crucial information can digital evidence analysis uncover?