DNA, Protein Synthesis and Epigenetics (Chapter 9) Flashcards
Structure of DNA
-Deoxyribonucleic acid is a double stranded helix
- It consists of repeating nucleotides
- Each nucleotide contains a deoxyribose sugar, a phosphate group, and 1 of 4 nitrogenous bases
- The DNA strands are connected by weak hydrogen bonds between base pairs
- Adenine always pairs with Thymine and Cytosine always pairs with Guanine
- The DNA strands run in opposite directions with one going from 3’ to 5’ and the other going from 5’ to 3’
Full name for DNA
Deoxyribonucleic acid
A nucleotide consists of
One phosphate, one deoxyribose sugar, one nitrogen base either Adenine, Thymine, Guanine, Cytosine
The two base pairs and number of hydrogen bonds
- A pairs with T and is joined by 2 hydrogen bonds
- G pairs with C and is joined by 3 hydrogen bonds
Chromatin
Coiled strands of DNA. For gene transcription
Chromosomes
Super coiled or condensed strands of DNA. For cell division
Histone
A protein that DNA wraps around in order to be packaged into the nucleus
Nucleosomes
Groups of histones packaged together
Gene
A section of DNA that codes for a protein. Each protein molecule has one gene
How is a gene coded?
By the sequence of nucleotides contained within it. Differences in this sequence of nucleotides provides variation.
Alleles
Variations of a gene
How many base pairs in a gene
Up to 1000, providing huge potential for variation
Mitochondrial DNA
Inherited from the mother through the egg cell. They are small circular strands of DNA, which are not bound to histone proteins. It contains 37 genes which are all essential for mitochondria to function .Around 5-10 in each mitochondria.
What is the difference between DNA and RNA
- DNA contains a deoxyribose sugar, RNA contains a ribose sugar
-DNA is double-stranded, RNA is single-stranded
-DNA is found in the nucleus, RNA is found in the nucleus and the cytoplasm
-DNA contains thymine, RNA contains uracil
-DNA contains genes, RNA transfers genetic code
-DNA is synthesised from itself, RNA is synthesised from DNA
DNA Replication
The process of duplicating DNA into two exact replicas, usually before a cell divides to ensure an even amount in each new daughter cell
Helicase
An enzyme that breaks the hydrogen bonds between nitrogen bases to create two single strands of DNA
Polymerase
An enzyme that helps free nucleotides in the nucleus to attach themselves to their complementary base partners.
Genome
An organism’s complete set of genetic information.
Synthesis
The process of combining smaller molecule to make larger molecules
DNA role in protein synthesis
DNA acts as a template that codes for the correct order in which amino acids are to be joined to the chain to make a protein
Two stages of protein synthesis
- Transcription in the nucleus
- Translation at ribosomes in the cytoplasm
Transcription definition
The process by which the genetic instructions are copied from the DNA to the mRNA molecule.
Translation definition
The production of a protein using the information that is coded in the mRNA molecule.
Transcription steps
- DNA molecules are too large to leave the nucleus, so the genetic code must be copied in messenger RNA (mRNA), which is small enough to pass through the nuclear pores of the nucleus
- to form the mRNA molecule the DNA is first unzipped by the helicase enzyme
- Then RNA Polymerase reads the template DNA strand from 3’ to 5’ and builds a single strand of mRNA that runs from 5’ to 3’ and is complementary to the template strand
- At the end of the gene there will be a section of bases that tell the RNA polymerase to stop coding (known as a stop codon)
- The non template strand, called the coding strand is not used in the process
- Before the mRNA can leave the nucleus, it must undergo splicing where the non-coding regions of the DNA strand called introns are removed from the strand
- This produces a strand that consists of just coding regions called exons
- These leftover exons are joined together by ligase
- The mRNA can then migrate out of the nucleus through the nuclear pores of the ribosomes
Translation steps
- In the cytosol, a ribosome attaches to one end of the mRNA molecule at a particular sequence of bases called the start codon (AUG)
- This ensures that the ribosome attaches to the correct end of the mRNA
- The ribosome reads the mRNA sequence in groups of 3 known as codons, which correspond to a specific amino acid
- Small molecules of RNA called transfer RNA (tRNA) bring the corresponding amino acid to the codon. One end of the tRNA binds to it’s corresponding amino acid, while the other end has a loop with 3 nitrogenous bases called an anticodon that is complementary to a specific codon.
- the amino acids are joined together by peptide bonds to form the protein chain
- Once each tRNA molecule delivers its amino acid, it detaches from the ribosome and can then pick up another amino acid from the cytoplasm
- Eventually a stop codon will come up, stopping translation and releasing the complete protein from the ribosome. The stop codons are UAA, UAG, UGA
gene expression
The process of copying information from DNA on to mRNA and then translating the message into a series of amino acids to form a protein.
Epigenetics definition
Changes in gene expression that result from environmental mechanisms other than changes in DNA sequence
Epigenome
Consists of the histones and other chemicals around the DNA sequence. It allows the body to control which genes to express at what time.
How can genes be regulated epigenetically?
Through changes in the chromatin
Histone acetylation
Where an acetyl group (CH3CO) is added to a histone protein, encouraging increased expression.
DNA Methylation
Adding a methyl group (CH3), which encourages decreased expression
Explain DNA Methylation
- Methyl group can only be added between a cytosine and guanine molecule
- the methyl group acts as a marker that means the DNA polymerase can’t bind to DNA for transcription
- Genes are basically switched off in this state
- Methylation increases with time as we become more and more exposed to varying environemtnal factors as we age
- some of the these methyl group markers can become imprinted and can then be passed onto offspring
Monozygotic twins
When identical twins develop from a single zygote, which for some reason divides and becomes 2 individuals
Dizygotic twins
where 2 eggs are fertiled by 2 sperm at the same time and do not have identical genetic code
