Topic 3: Genetics Flashcards
What is DNA?
- DNA is genetic information for an organism.
- It is passed from parents to offspring
- Stands for Deoxyribonucleic Acid.
Where is DNA in a cell?
In the nucleus
What is the structure of DNA?
- DNA is shaped like a twisted ladder (double helix)
Definition of a chromosome?
- Tiny threads that are made of DNA
- The shape DNA takes when it is coiled up
Definition of a gene?
- A gene is a segment of DNA that codes for a specific protein
Describe the relationship between
chromosomes, DNA and genes?
- There are 46 chromosomes inside a human nucleus
- Chromosomes are made up of DNA
- Chromosomes contain genes that determine the traits of an organism
What is a nucleotide?
- The basic building block of DNA
- Nucleotides are made up of a phosphate group, a deoxyribose sugar and a nitrogenous base
What are the 4 bases in DNA? What base
pairs with what?
DNA has four different bases:
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
- Nucleotides are joined together by their sugar-phosphate groups.
A pairs with T
G pairs with C
T pairs with A
C pairs with G
What bonds hold together the bases in DNA?
- Hydrogen bonds hold together the nitrogenous bases.
What is RNA?
- A ribonucleic acid, that is present in all living cells. Its main role is to act as a messenger carrying instructions from DNA for controlling the synthesis of proteins.
- Divided into 3 types (mRNA, rRNA, tRNA)
List the differences between DNA and RNA?
- DNA is double-stranded, RNA is single-stranded
- DNA has a deoxyribose sugar, RNA has a ribose sugar.
- DNA uses Thymine (A), RNA uses Uracil (A)
- DNA is located in the nucleus, RNA is located in the nucleus and cytoplasm.
What pairs with adenine (mRNA)?
Uracil
Similarities between DNA and RNA
- Uses Guanine, Cytosine, and Adenine
- Has a sugar-phosphate backbone.
What is protein synthesis?
The process in which cells make proteins through transcription and translation
What are the 2 steps of protein
synthesis?
Protein synthesis involves 2 important steps:
Transcription (DNA → mRNA)
Translation (mRNA → protein)
What happens during transcription?
- DNA to mRNA
- Transcription is the first step of protein synthesis.
It is broken into three major steps:
Step 1: Initiation (RNA polymerase binds onto the promoter)
Step 2: Elongation (RNA polymerase moves across the DNA strand and synthesises)
Step 3: Termination (Ending of transcription, the mRNA strand is complete and it detaches from DNA) - Transcription occurs in the nucleus only
What happens during translation?
- mRNA to protein
1. mRNA connects to a ribosome
2. tRNA brings amino acids
3. Amino acids join together
4. Protein is finished and released. - Translation occurs in the cytoplasm and at the ribosome.
What is mRNA? What is its function?
- mRNA stands for messenger ribonucleic acid.
- mRNA carries the instructions for one gene
- mRNA is synthesised in the nucleus
- Its function is to make a copy of a gene and take it to a ribosome, where amino acids are assembled to make a protein
What is rRNA? What is its function?
- rRNA stands for ribosomal RNA
- The rRNA is responsible for linking the amino acids in a pre-determined order to form proteins.
What is tRNA? What is its function?
- tRNA stands for transfer RNA
- tRNA molecules ferry the amino acids to the mRNA at the ribosome
- tRNA links with the ribosome and matches its anticodon with the codon of the mRNA
- A peptide bond forms between the adjoining amino acids, forming a polypeptide. The tRNA is removed to be used again.
What is the role of the ribosome?
To translate the genetic code transcribed in mRNA into an amino-acid sequence
What is a codon?
Three nucleotides found on the mRNA that codes for a specific amino-acid.
What is an anticodon?
Three nucleotide sequences found on the tRNA that bind with the mRNA sequence
What is a triplet?
A sequence of three nucleotides that determines ONE amino acid
What is a polypeptide chain?
A string of amino acids connected by peptide bonds. They are the building blocks for proteins or amino acids.
How are polypeptide chains and proteins different?
A polypeptide is a chain of amino acids linked together by peptide bonds. Whereas the protein is made up of one or more polypeptide chains folded to a specific three-dimensional structure, in which determines its functions.
What is tRNA? What is the role of tRNA?
- Is a small RNA molecule that helps decode mRNA sequences into proteins.
- It brings specific amino acids to the ribosomes during translation, the process of assembling proteins based on instructions provided by the mRNA.
What are mutations?
Changes in the DNA sequence of an organism
When do mutations occur?
DNA mutations occur during cell division (mitosis) where abnormal cells are replicated
What can mutation be?
- Harmful (benign or malignant)
- Beneficial (HIV resistance, lactose tolerance)
- No effect on organism
What causes them?
- Can come about spontaneously due to errors in DNA replication
- Induced by mutagens (environmental factors that cause changes in DNA) such as
- X-rays/radiation
- Chemicals, poisons
- UV Light
What is a point mutation?
A change in a single nucleotide base in a DNA sequence. This can be a substitution of one base for another (eg; A to G). This changes the codon in the mRNA and potentially the amino acid in the protein.
What is addition/insertion mutation?
The addition of one or more nucleotide bases into the DNA sequence. Eg; if an extra cytosine is added, it shifts the reading frame and changes all downstream codons, resulting in a completely different/non-functioning protein.
What is deletion mutation?
The loss of one or more nucleotide bases in the DNA sequence. They cause frameshift mutations if they are not in multiples of 3, altering the downstream amino acid sequence.
How do mutations impact protein synthesis?
- DNA affected (Substitution, Insertion, or deletion)
- This results in the mRNA being copied incorrectly. (incorrect nucleotide sequences)
- Codes for wrong amino acid(s).
- Formation of incorrect protein
What is Huntington’s Disease?
A progressive brain disorder that affects the central area of the brain as well as movement, mood, and thinking skills.
What is Sickle cell anaemia?
An inherited blood disorder marked by defective haemoglobin.
What happens in Sickle cell anaemia?
- Only one amino acid changes in the haemoglobin
- The haemoglobin still function but folds differently, changing the shape of the red blood cell, and affecting the way it carries oxygen
- Blocks blood, causes tissue damage and pain.
