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Nucleic Acids - DNA and RNA Flashcards

Nucleic Acids – DNA and RNA

Developed by Joshua Weinstein, his "DNA microscope" shows the location of DNA and RNA, down to the identity of individual nucleotides.

Summary of Presentation

Brief Structure of the Nucleus
Structure of Nucleic Acids
DNA
RNA
DNA Replication
DNA Fingerprinting

Structure of the Nucleus

The nucleus is found in both plant and animal cells.
It's usually in the center of animal cells.
In plant cells, it's pushed to the side by the large vacuole.
The nucleus contains the following parts:
- Endoplasmic reticulum: A network of membranes involved in protein and lipid synthesis.
- Nucleolus: The site of ribosome production.
- Chromatin: The complex of DNA and proteins that make up chromosomes.
- Nucleoplasm: The gel-like substance inside the nucleus.
- Nuclear pore: A channel in the nuclear envelope that regulates the movement of molecules between the nucleus and cytoplasm.
- Nuclear envelope: The double membrane that surrounds the nucleus and separates it from the cytoplasm.

Nuclear Membrane

The nucleus is surrounded by a double membrane called the nuclear membrane or nuclear envelope.
This membrane is connected to the endoplasmic reticulum.
The nuclear membrane has pores that allow for the transport of molecules into and out of the nucleus.

Nucleoplasm

The ground substance inside the nuclear envelope is called nucleoplasm or nuclear sap.

Contents of Nucleoplasm

The nucleoplasm contains:
- Free nucleotide bases: These are the building blocks of DNA and RNA.
- The nucleolus: The site of ribosome synthesis.
- The chromatin network: The DNA and protein complex that forms chromosomes.
The nucleolus is in the middle of the nucleoplasm and is responsible for making and containing RNA.

Chromatin Network

The chromatin network is a tangled mass of thread-like structures.
Each thread-like structure is a chromosome, which is made of two chromatids held together by a centromere.
Each chromosome contains sections of DNA called genes.

Function of the Nucleus

The nucleus controls all cell activities.
DNA in the nucleus is responsible for protein formation.
Hormones and enzymes are proteins.
Hormones and enzymes control metabolic reactions.
The nucleus transmits hereditary characteristics from parent to offspring.

Nucleic Acids Structure of Nucleic Acids

RNA and DNA are called nucleic acids.
Nucleic acids are organic molecules that control protein synthesis.
Nucleic acids are made of building blocks called monomers.
The monomers for RNA and DNA are nucleotides.

Structure of a Nucleotide

Each nucleotide is made of 3 parts:
- Phosphate (P): A chemical group consisting of a phosphorus atom and four oxygen atoms.
- Sugar (S): A five-carbon sugar molecule (deoxyribose in DNA, ribose in RNA).
- Nitrogen base (NB): A molecule containing nitrogen and having chemical properties of a base.

Terminology

TERM: Nucleotides
DEFINITION: Monomers or building blocks of nucleic acids.
USE IN SENTENCE: The nucleotide of DNA has deoxyribose sugar while that of RNA is made up of ribose sugar.

DNA

DNA stands for deoxyribonucleic acid.
Types of DNA:
- Nuclear/Chromosomal DNA: Found within the nucleus.
- Mitochondrial DNA: Found in the mitochondria.
- Chloroplastic DNA: Found in the chloroplasts of plant cells.

Location of DNA

DNA found within the nucleus = nuclear DNA.
DNA found outside the nucleus = extra-nuclear DNA.
Extra-nuclear DNA in the chloroplast = chloroplastic DNA.
Extra-nuclear DNA in the mitochondrion = mitochondrial DNA (mtDNA).

Terminology

TERM: Nuclear DNA
DEFINITION: DNA that is found within the nucleus.
USE IN SENTENCE: The nuclear DNA contains hereditary information.

Terminology

TERM: Extra-nuclear DNA
DEFINITION: DNA that is found outside the nucleus.
USE IN SENTENCE: Chloroplastic DNA is an example of extra -nuclear DNA because it is found in the chloroplast and not in the nucleus.

Discovery of DNA

James Watson and Francis Crick researched at the University of Cambridge in England.
Rosalind Franklin and her assistant, Maurice Wilkins at King’s College London took an X-ray photograph of DNA in 1952.
Franklin guessed DNA had a helix shape.
Wilkins showed the photograph to Crick without permission.
On 25 April 1953, Watson and Crick formulated the double helix structure of DNA.
X-ray photograph of DNA

Further Discoveries

Watson used these pictures in his study.
Watson and Crick continued the research.
They discovered:
- DNA has similar amounts of cytosine and guanine.
- DNA has similar amounts of adenine and thymine.
- This led to the idea of complementary base pairs.
- This led to the idea that DNA can make exact copies of itself.

Later Events

In 1958, Rosalind Franklin died of cancer.
In 1962, Watson, Crick, and Wilkins received a Nobel Prize for their work.
In the 1960s, further research was done in DNA replication, RNA, and protein synthesis.

DNA Structure

DNA is made of nucleotides.
Each nucleotide has:
- Phosphate
- Deoxyribose (sugar)
- Nitrogen base
Nitrogen bases in DNA:
- Adenine (A)
- Guanine (G)
- Cytosine (C)
- Thymine (T)
Two types of nitrogen bases:
- Purines (larger):
- Adenine (A)
- Guanine (G)
- Pyrimidines (smaller):
- Thymine (T)
- Cytosine (C)

Nucleotide Bonding

Nucleotides connect:
- The sugar of one nucleotide bonds to the phosphate of another.
- This forms a sugar-phosphate backbone.
- These bonds create long, ladder-like strands.

Base Pairing

Nitrogen bases are held together by weak hydrogen bonds.
Specific base pairing:
- Adenine pairs with Thymine (2 hydrogen bonds)
- Guanine pairs with Cytosine (3 hydrogen bonds)
These pairs are complementary base pairs and are always in equal numbers.

Terminology

TERM: Complementary base pairs
DEFINITION: Nitrogen bases that always pair with each other.
USE IN SENTENCE: Adenine and thymine are complementary base pairs because adenine always pairs with thymine in a DNA molecule.

DNA Structure

The DNA molecule is double-stranded (like a ladder).
This "ladder" twists to form a double helix.

Terminology

TERM: Double Helix
DEFINITION: Shape of the DNA molecule
USE IN SENTENCE: DNA is made up of 2 strands of nucleotides that are joined together and then twists to form a double spiral shape called the double helix.

DNA's Role – Genes

DNA carries hereditary information in genes.
A gene is a short segment of DNA with a specific base sequence.
DNA carries the genetic code for protein synthesis.
This code determines the amino acid sequence and the protein that will be made.

DNA's Role - Non-Coding DNA

Only 2% of DNA codes for proteins.
The rest (98%) is non-coding DNA.
Non-coding DNA is different for each individual and is used in DNA profiling/ DNA finger printing.

Terminology

TERM: Gene
DEFINITION: Refers to a small portion of DNA that carries genetic code for the formation of a particular trait or characteristic.
USE IN SENTENCE: The gene can also carry the code for the formation of a protein.

Terminology

TERM: Non-coding DNA
DEFINITION: Portions of DNA that do not carry any codes.
USE IN SENTENCE: Some parts of the DNA molecule do not have any codes these are called non- coding DNA.

Mitochondrial DNA (mtDNA)

mtDNA is not related to nuclear DNA.
It is shorter and circular.
mtDNA codes for enzymes that control respiration in the mitochondria.
mtDNA is inherited only from the mother.
It is used to trace maternal lineages because it has few changes or mutations.

Functions of Nuclear DNA

Controls the synthesis of proteins.
Transmits hereditary characteristics from parent to offspring.

RNA

RNA stands for Ribonucleic acid.
Types of RNA:
- Ribosomal RNA (rRNA): A type of RNA that is a component of ribosomes.
- Messenger RNA (mRNA): Carries the genetic code from DNA to ribosomes.
- Transfer RNA (tRNA): Transfers amino acids to ribosomes during protein synthesis.

Location of RNA

Ribosomal RNA (rRNA) is found in the cytoplasm where ribosomes are located.
Messenger RNA (mRNA) is found in the nucleus and attached to ribosomes in the cytoplasm.
Transfer RNA (tRNA) is found in the cytoplasm.

Structure of RNA

RNA is made of nucleotides.
Each nucleotide has:
- A sugar
- A phosphate
- A nitrogen base
The sugar in RNA is ribose.
RNA has 4 nitrogen bases:
- Cytosine (C)
- Guanine (G)
- Adenine (A)
- Uracil (U) (Uracil replaces thymine)

RNA Structure (Differences from DNA)

RNA is single-stranded.
RNA strands are shorter than DNA strands.
RNA strands are not coiled around histone proteins.
The bases in RNA occur in any number and ratio.

Functions of RNA

RNA plays a role in protein synthesis.
mRNA carries the genetic code from DNA to ribosomes.
tRNA picks up amino acids and takes them to ribosomes.

Differences between DNA and RNA

Feature	DNA	RNA
Location	Mainly in the nucleus	In nucleus & cytoplasm
Strands	Double-stranded	Single-stranded
Shape	Coiled (double helix)	Not coiled
Length	Long strands	Shorter strands
Nitrogen Base	Has thymine	Has uracil (no thymine)
Sugar	Deoxyribose	Ribose
Base Pairing	Equal base pair numbers	Any base number/ratio

DNA Replication

Unwind and unzip:
- An enzyme (helicase) breaks weak hydrogen bonds between base pairs, separating the two strands of the DNA molecule of the parent cell.
Template forms:
- Each strand acts as a template for the formation of a new complementary strand of DNA, forming two sets of DNA.
Nucleotides pair up:
- Free nucleotides in the nucleus pair up with the bases on the exposed single DNA strands.
- An enzyme, DNA polymerase, matches the bases on the template with the free nucleotides through complementary nitrogenous base pairing.
Bases pair up:
- Pyrimidine bases (thymine and cytosine) pair with purine bases (adenine, guanine).
Helix forms:
- There are now two identical molecules of DNA, both of which are double-stranded.
- Each one twists to form a helix.

The Process

The DNA double helix unwinds (Figure 7A)
The weak hydrogen bonds between the nitrogenous bases are broken. The DNA strands separate (they unzip)(Figure 7B)
Each original DNA strand serves as a template on which its complement is built (Figure 7C)
Free nucleotides build a DNA strand onto each of the original DNA strands, attaching their complementary nitrogenous bases (A to T and C to G) (Figure 7D)
This results in two identical DNA molecules. Each molecule consists of one original strand and one new strand (Figure 7E).

DNA replication is important for cell division, particularly mitosis.
- It allows each chromosome to be copied so that each new identical daughter cell produced contains the same number and type of chromosomes.
DNA replication is the process where DNA makes an exact copy of itself.
Histones (proteins) also duplicate during this process.
DNA replication occurs during Interphase, before cell division.
- It happens at the start of mitosis and meiosis, during interphase.
I: Interphase _ P: prophase M: metaphase A: anaphase T: telophase ***_ C: cytokinesis

The Process

The original DNA is called parent DNA.
The double helix DNA molecule unwinds.
This forms a ladder-like structure.

Unzipping

The weak hydrogen bonds between nitrogen bases break with the help of the enzyme Helicase.
The DNA strands unzip, forming 2 single strands.
These single strands are templates for new DNA strands.

Nucleotides and Enzymes

Free-floating nucleotides are in the nucleoplasm.
These nucleotides attach to complementary bases.
DNA polymerase enzymes control this process.

Daughter Strands

Two new identical DNA molecules are formed.
The new strands are called daughter strands.
Each new DNA has one original strand and one new strand.

Significance

DNA replication makes an exact copy of DNA.
This creates identical copies of chromosomes in the cell.
DNA replication ensures identical cells are produced at the end of mitosis.
It also ensures these cells are identical to the parent cell.

Terminology

TERM: DNA Replication
DEFINITION: The process by which DNA makes an exact copy of itself.
USE IN SENTENCE: At the end of DNA replication there are 2 copies of DNA that are identical to each other.

DNA Fingerprinting/Profiling

DNA is extracted from cells to make a barcode.
The barcode's pattern shows the person's inherited base pair sequence.
This barcode is a DNA profile/fingerprint.

DNA Profile Uniqueness

Non-coding DNA is used to determine this profile, because it is highly variable amongst individuals, except for twins.
Each person (except identical twins) has a unique DNA profile.
DNA is used as forensic evidence from crime scenes.

DNA profiling process

Collect DNA: Obtain biological sample such as blood, saliva, or hair.
Extract DNA: Isolate DNA from cells in the sample.
Amplify DNA (PCR): Make many copies of specific DNA regions (STRs) using polymerase chain reaction (PCR).
Separate Fragments (Electrophoresis): Separate DNA fragments by size in a gel using electrophoresis.
Visualize & Analyze: View banding patterns and compare between samples to create a DNA profile.

PCR

Polymerase Chain Reaction (PCR) multiplies small amounts of DNA into millions of copies.
PCR replicates DNA.
This ensures enough DNA for testing.
Steps in the process of DNA fingerprinting

Uses of DNA Profiling

Identify crime suspects: Match DNA from crime scene evidence to suspects.
Proof of paternity: Determine biological father of a child.
Determine genetic disorders/defects: Identify genes associated with diseases.
Trace missing people: Compare DNA of unidentified remains to family members.
Identifying dead persons: Match DNA to personal items.
Establish tissue compatibility for organ/tissue transplant: Ensure donor and recipient are a match.
Fighting illegal trade: Identify protected species involved in poaching or illegal trading.

Reliability Concerns

A small DNA piece used might not be unique.
Private labs may not follow standards, questioning results.
Human error can occur in result interpretation.

Ethical Issues

DNA profiling is expensive, limiting some suspects' defense.
DNA analysis can reveal personal information, which can be misused.
Potential for abuse of DNA by criminals or government.
Discrimination based on genetic information.
Debates about ownership of DNA databases.

Ethics of Obtaining DNA Samples

DNA samples cannot be taken without consent.
It can violate the right of privacy, by being able to access individuals information.
Abuse of DNA by criminals or government.
Discrimination can occur due to genetic information.
Debated ownership of the DNA database.

Terminology

TERM: DNA fingerprint / DNA profile
DEFINITION: Black bars that are left behind on x-ray film when an extract of DNA undergoes a biochemical process.
USE IN SENTENCE: DNA fingerprints are useful in identifying suspects in criminal investigation.

Terminology

TERM: DNA fingerprinting/DNA profiling
DEFINITION: The process of identifying an individual by comparing their DNA with that of another known DNA.
USE IN SENTENCE: DNA fingerprinting is used by forensic scientists to identify siblings.

Terminology:

Nucleotide: A monomer or building block of nucleic acids.
Nuclear DNA: DNA found within the nucleus.
Extra-nuclear DNA: DNA found outside the nucleus.
Complementary base pairs: Nitrogen bases that always pair with each other.
Double Helix: The shape of the DNA molecule.
Gene: A small portion of DNA that carries the genetic code for a particular trait or characteristic.
Non-coding DNA: Portions of DNA that do not carry any codes.
DNA Replication: The process by which DNA makes an exact copy of itself.
DNA fingerprinting/DNA profiling: The process of identifying an individual by comparing their DNA with that of another known DNA.

FINAL ASSESSMENT QUESTIONS:

Questions 1-20

QUESTION 1

Of the following list of molecules: Which combinations represents components of a nucleotide?

Sugar
Phosphate
Nitrogenous base
Amino acid
A. i, ii and iv only

B. i, ii and iii only

C. i, ii, iii and iv

D. ii, iii and iv

QUESTION 2

As DNA was extracted from cells of E. coli, it was analyzed for nitrogen base composition. It was found that 38% of the bases were cytosine. What percentage of the bases is adenine?
A. 12

B. 24

C. 38

D. 62