26-10-21 - Introduction to Molecular Biology 1 Flashcards
What are the sugars found in RNA and DNA?
How do they differ in structure?
What are the bonds that join sugars together in DNA and RNA?
What are they formed between?
What do these linked sugars form in DNA and RNA?
- Ribose – found in mRNA
- Deoxyribose – found in DNA
- Deoxyribose is missing an oxygen hydroxy group on carbon 2 that is present on Ribose
- Sugars are joined together via 5’ – 3’ Phosphodiester bonds, which are strong covalent bonds
- The sugars are joined together via a phosphate attached to a carbon 3 oxygen from one sugar, and carbon 5 oxygen from another sugar
- This results in there being a 5’ end and a 3’ end, and forms the sugar phosphate backbone of DNA and RNA
What are the 4 bases that are in the structure of DNA?
What are the 2 different types?
Which ones pair up?
How do these differ with bases in Mrna?
- Adenosine and Guanine – purines (double ring)
- Thymine and Cytosine – pyrimidines (single ring)
- Adenosine pairs with Thymine
- Guanine pairs with Cytosine
- RNA contains Uracil instead of Thymine
- Thymine contains an extra methyl group than Uracil.
What is the structure of DNA like?
- DNA consists of a double helix structure
- It is known as a beta helix, as it is right-handed
- 2 adjacent strands run anti-parallel to each other, with one running from 5’ to 3’, and the other running from 3’ to 5’
- Each DNA strand consists of deoxyribonucleoside-triphosphates (nucleotides) Linked together via 5’ – 3’ phosphodiester bonds
- These nucleotides contain 3 phosphate groups attached to a deoxyribose sugar, which is attached to a nitrogenous base.
- Bases from each strand form hydrogen bonds with bases from the adjacent strand
- Purines pair with Pyrimidines
- There are 2 hydrogen bonds between adenine and thymine, and 3 hydrogen bonds between cytosine and guanine
- There is a sugar phosphate backbone that runs down the back of DNA, with phosphates on the outside of the structure, and sugars and bases in the middle.
- The sugar phosphate backbone is negatively charged.
How can chromosomes be stained?
What is the name given to this technique?
What does it produce?
What is another way chromosomes can be distinguished?
How many chromosomes are in humans?
What are the 2 types of chromosomes?
- Chromosomes become more condensed in certain stages of mitosis
- The nucleus can be dropped onto a microscope slide, the chromosomes will spread out, allowing them to be stained
- This is a cytogenetics technique known as g-banding, which produces a karyotype
- Chromosomes can also be distinguished by size, with chromosome 1 being the longest, and chromosomes 1 being the longest, and 21 being the shortest
- There are 46 chromosomes in humans arranged into 23 pairs
- 44 are autosomal (non-sex) and 2 are sex chromosomes e.g XX for girls and XY for boys
What is another method for identifying chromosomes?
How does it work?
- Another method for identifying chromosomes is fluorescent marking
- Complimentary probes of DNA can be manufactured that match the DNA trying to be analysed
- These probes have fluorescent markers on them
- When the DNA strands are separated, they naturally want to be in a double helix structure, so they bind to the complementary fluorescent probe, which allows an image of the chromosomes to be made.
What are the different parts of a chromosome?
What do they allow for?
- The chromosome has a telomere and a centromere
- The centromere allows for the separation of DNA to opposite ends during mitosis.
What does a nucleosome consist of?
What different forms of proteins does it contain?
What turns does it contain?
How does charge aid in the formation of nucleosomes?
What protrudes from the structure?
What do multiple nucleosomes form?
What aids in further condensing of this structure?
- A nucleosome consists of 147 base pairs of DNA double helix rapped around an octameric histone core consisting of 8 histone proteins, with each histone containing alpha helices.
- There are 4 types of histone proteins: H2A, H2B, H3 and H4
- The DNA is rapped around the histones with 1.7 left-handed turns
- The sugar-phosphate of DNA is negatively charged, and the histone proteins are positively charged, which allows for binding
- Histone proteins have a long N-termini (amino), which protrudes from the structure
- Multiple histones form a ‘beads on a string’ like structure form of chromatin
- Histone H1 provides a unique roil in anchoring the DNA to the histone and telling it to keep folding in the right direction, which aids in forming the more condensed 30nm fibre of packed nucleosomes
- This structure is condensed further until a chromosome is formed.
How does function of DNA relate to its position of the scaffold?
• DNA that is used is in more open positions, and anchored further away from the scaffold
How are proteins condensed during the cell cycle?
• Enzymes called condensins allow proteins to adopt a very tight structure
When do proteins need to be remodelled?
How is this done?
- Chromosomes need to be remodelled to allow protein access in order to use the genetic information
- This is done using a remodelling complex and requires energy in the form of ATP.
What is epigenetic modification?
What is an example of this and why is it done?
What is an example of a modification within this example?
What does this modification do?
- Epigenetic modification are changes in gene expression that do not cause changes in the DNA sequence.
- An example of this is post-translational modification (PTM) of histone proteins
- This influences how tightly packed a particular section of DNA is.
- Phosphorylation, methylation, and acetylation
- Acetylation removes the positive charge from the histones, which decreases binding with negatively charged DNA, causing a relaxation of the structure.
How many base pairs are in DNA of the entire genome?
What % of our genome codes for proteins?
- There are 3 billion base pairs in DNA of the entire genome
- Approximately 1.5% of our genome codes for proteins, with the rest being junk protein
What are the 2 different types of repetitions in DNA?
What do repeats contribute to?
- Interspersed repeats
- These sequences present many times within the genome, but the repeats appear in difference places e.g different chromosomes
- There are SINE and LINE interspersed repeats, which are often derived from retroviruses (RNA viruses which insert DNA copy of their genome into the host cell in order to replicate e,g HIV)
- Short/long interspersed nuclear elements
- Short may be a few hundred base pairs long
- Long may be several thousand base pairs long
- Interspersed repeats contribute around 1/3 of the genome
- Tandem repeats
- These are shorter sequences that are repeated many times consecutively within a particular region of a chromosome
- There are 3 different types of Tandem repeats:
- Satellites e.g telomere TTAGGG
- Minisatellites – 7-100 bases repeated up to 40,000 bases
- Microsatellites – 1-6 bases repeated more than 100 bases
• Repeats contribute to diversity in individuals
Why are repeats important in forensics?
- If a sample is obtained from a crime scene, we can look at the numbers of consecutive repeats at different locations, which will be different for different people
- The forensic sample and samples from suspects can be used in gel electrophoresis to identify the matching repeats
- This will allow the perpetrator to be identified.
What is myotonia?
What is causes myotonic dystrophy?
Why can muscular dystrophy worsen through generations?
- Myotonia refers to the inability to relax muscles at will
- Myotonic dystrophy is caused by a tri-nucleotide repeat that occurs many times in a row at a particular location (3 bases repeating)
- For most people the tri-nucleotide repeat is in a number range that does not cause any problems
- If the repeat number becomes larger, this can lead to muscular dystrophy.
- When chromosomes are passed on via miosis (cell division that produces reproductive cells), this can lead to the increase expression in the number of repeats
- An increased number of repeats is associated with a greater severity in the condition.
Where are mitochondria inherited from?
What does this mean from implications of disease?
What else is mitochondria used for?
- Mitochondria are maternally inherited (only from mothers)
- This means if there is a defect of mitochondria that causes disease, this will only come from the maternal line.
- Mitochondria is also useful for looking at human lineage, and shows how humans migrated across the world
- We are thought to all originate from Africa.
