DNA Flashcards
what does DNA stand for
DeoxyriboNucleic Acid
what is DNA + location
- molecule of heredity
DNA is a molecule found in cells specifically in the nucleus in the mitochondria, that contains the genetic information that determines the structure of the cell and the way it functions.
nuclear DNA structure
Nuclear DNA strands the wrap around 8 Proteins are called histones to form nucleosomes.
chromatin
The coiled DNA forms are tangled network called chromatin.
chromosomes
Super coiled, structures of chromatin are called chromosomes.
- 46 chromosomes in somatic cell
- 23 chromosomes in gamete
histones and nucleosomes importance
Histones and nucleosomes are important in the packaging of DNA to produce
chromosomes
polymer
Polymer/long macromolecule (many repeating small units) consisting of Two helical chains coiled around a common axis
nucleotides
The building blocks or monomers of these chains are called nucleotides
Each nucleotide consists of 5 carbon sugar (deoxyribose) , a phosphate sugar and a nitrogen containing organic base (nitrogenous base)
base pairing rule
Base Pairing Rule: The base adenine always bonds with thymine (A-T), and cytosine always bonds with guanine (C-G)
purines
Purines: the larger bases (Adenine and Guanine)
pyrimidines
Pyrimidines: the smaller bases (Cytosine and Thymine)
number of hydrogen bonds between bases
three hydrogen bonds between cytosine and guanine
two hydrogen bonds between thymine and adenine
polynucleotides
two poly nucleotide strands held together by weak hydrogen bonds,
the poly nucleotides held together by covalent bonds between sugar and phosphate
complimentary pairs
bases that are paired together are called complimentary pairs
order of bases determine _________
genetic code
length of DNA
2-3m
genes
Genes are sections of DNA
Genes contain instructions for the construction of a particular protein, or RNA
introns and exons
Genes consist of introns and exons
Exons are sections of coding DNA, that is they contain instructions for making proteins
Introns are sections of non-coding DNA, that is they do not contain instructions of making proteins but are now believed to serve other important functions
mitochondrial DNA
1% of all DNA in cell which is important for the functioning of mitochondria, there’s five to ten molecules of mtDNA in a mitochondrion
mitochondrial genes
Mitochondrial DNA carry about 37 genes
- 24 genes contain the code to make tRNA
- 13 make enzyme’s
the mitochondrial genes are responsible for the construction of several important enzymes involved in cellular respiration (aerobic), releasing energy for the cell
mitochondrial genes are inherited from the mother only
structure of mitochondrial DNA
circular molecule that is not bound to proteins
mtDNA vs nuclear DNA
- Nuclear DNA is in the form of very long strands that are bound to proteins, the histones
- mtDNA is in the form of small circular molecules that are not bound to proteins
where does DNA replication occur
it occurs in nucleus
enzymes involved in DNA replication
- helicase
- primate
- DNA polymerase
- ligase
- topoisomerase
helicase
Helicase, breaks Hydrogen bonds is the enzyme which unzips the the DNA molecule exposing the nitrogen base code, each exposed strand acts as a pattern or template for the construction of a new DNA molecule
DNA polymerase
initiated by primase,
DNA polymerase works its way along the template strand and add new nucleotides e.g A to T, C to G
Nucleotides pair with complementary nucleotide on the existing strand.
primase
makes Primer which consists of nucleotides
direction of DNA polymerase
Polymerase goes in the direction of 5 prime to 3 prime
ligase
DNA ligase seals up the DNA again.
result of DNA replication
Two new copies of DNA have been made.
importance of DNA replication
Importance: DNA must replicate so that viable daughter cells are formed.
leading and lagging strands
L strands travel from 5 prime to 3 prime, the new strand of the template strand that goes from 5’ to 3’ is the lagging strand, the new strand of the template strand that goes from 3’ to 5’ is the leading strand
functions of proteins made by DNA
- Body Defense - Antibodies are specialized proteins made by some white blood cells involved in killing invading microbes(foreign invaders)
- Contractile Proteins - are responsible for movement. Examples include actin and myosin. These proteins are involved in muscle contraction and movement.
- Enzymes - are proteins that facilitate chemical reactions. They are often referred to as catalysts because they speed up chemical reactions.
- Hormonal Proteins - are messenger proteins which help to coordinate certain bodily activities. Examples include insulin, oxytocin.
- Structural Proteins - are fibrous and stringy and provide support. Examples include collagen, and elastin. Found in connective tissues like ligaments, tendon s and cartilage.
- Transport Proteins - are carrier proteins which move molecules from one place to another around the body or through cell membranes. Examples include hemoglobin, carrier proteins and channel proteins.
types of proteins + function
actin/myosin: muscle contraction
fibrin: blood clotting
amylase: enzyme that breaks down starch
haemoglobin: oxygen carrying molecule in red blood cells
DNA and RNA (differences)
location:
- DNA: nucleus and mitochondria, RNA: nucleus and cytoplasm
strand:
- DNA: double strand, RNA: single strand
bases:
- DNA: thymine + paired, RNA: uracil + single
sugar molecule:
- DNA: deoxyribose, RNA: ribose
sequence of bases in DNA controls….
the order of amino acids and therefore the type of protein that is produced.
what does RNA stand for?
RiboNucleic Acid
three types of DNA
- messenger RNA (mRNA)
- ribosomal (rRNA)
- transfer RNA (tRNA)
functions of mRNA
- made in the nucleus
- takes the genetic code into the cytoplasm allowing the genetic code to be read by ribosomes
functions of rRNA
- makes up most the mass of ribosomes, rest is protein
- it ensures the correct alignment of mRNA, tRNA and ribosome
- has an enzymatic role in the formation of peptide bonds between amino acids
function of tRNA
is able to carry a specific amino acid and therefore plays a vital role in protein synthesis
codon
codon is a sequence of three bases in mRNA
protein synthesis
- transcription
- splicing
- translation (LATE)
what is transcription
the process by which the genetic instructions are copied (or transcribed) from the DNA to the mRNA molecule.
when does transcription occur?
when triggered by chemical messengers that enter the nucleus from the cytosol and bind to the DNA at the relevant gene
process of transcription
- helicase makes the double stranded DNA come apart, separates about 17 base pairs at a time
- RNA polymerase to begin the process of making mRNA, transcribing the bases on one strand of the DNA to make a complementary molecule of mRNA (joins nucleotides with bases that are complementary to those on the DNA template strand)
- when there is a cytosine base on the DNA, a guanine will be added to the mRNA
- when there is a guanine base on the DNA, a cytosine will be added to the mRNA
- when there is a thymine base on the DNA, an adenine will be added to the mRNA
- when there is an adenine base on the DNA, a uracil will be added to the mRNA
- the strand that is copied is called the template strand because it is the template from which the mRNA is made
- the other DNA strand is known as the coding strand
- because the bases always form complementary pairs, the order of bases on the coding strand will be the same as in the mRNA molecule
- mRNA moves into the cytoplasm through a nuclear pore
RNA processing/splicing
- Before the mRNA leaves the nucleus the non-coding introns are removed and the coding exons are joined together.
- The number of exons joined together and the way they are joined together may not always be the same.
- This means that the same piece of DNA can code for different polypeptide chains.
what is translation?
Translation takes place in the ribosomes that are found in the cytoplasm. This is where the messenger RNA is ‘interpreted’ and the new protein formed.
stages of translation
- The one end of the mRNA called the start codon attaches to a ribosome. The ribosome “reads” the mRNA.
- The ribosome decodes the mRNA in groups of three–base triplets or codons–which are complementary to bases in transfer RNA (tRNA). Transfer RNA joins to the mRNA. The sequence of three bases matching the codon is called the anticodon, these determine the amino acid carried by tRNA.
- The tRNA is specific to an amino acid that it collects and returns to the mRNA.
- The amino acids are now lined up in order of the instructions (correct sequence) on the mRNA.
- peptide Bonds form between the amino acids and a polypeptide chain is formed. For each bond formed between the amino acids, the energy from the breakdown of one ATP molecule is required
- The polypeptide chain folds and becomes a specific shape forming a protein, this is how the protein becomes functional.
- Once the tRNA has delivered its amino acid, it detaches from the ribosome and can then pick up another amino acid from the cytosol.
introns and exons in mRNA
pre-mRNA includes introns and exons
final mRNA includes only exons
how are multiple copies of the same protein produced?
one mRNA molecule may be read by many ribosomes to the same time, producing multiple copies of the protein
lipid and carbohydrate synthesis
no genes carry instructions to code for lipids and carbs
synthesis requires enzymes (proteins)
genes control the synthesis of lipids and carbs
gene expression
gene expression is the process of copying information from DNA into mRNA (transcription) and the translating the message into a series of amino acids to form a protein
switched off genes meaning
genes that are not being used to make mRNA are said to be switched off
how are genes switched on/off?
genes maybe switched on acetyl tags (acetylation) (activate) on the histones or switched off by methyl groups (methylation) (mess up)
histones
histones organise the chromatin that form the chromosome
histones prevent strands of DNA becoming tangled
histones also affect gene expression
what happens when some of the amino acids in a histone change?
- alters the way DNA filaments are coiled around that histone
- enhance or repress gene expression
- when cell replicates the histone also replicates
acetylation
is a form of histone modification that enhances gene expression
acetyl tags are on the tail of the histone proteins which allow easier access to DNA
regulates gene expression by opening or closing the chromatin structure
Acetyl molecules = access = tags on histone = loosely wound gene = turns gene expression on
histone modification other than acetylation
another histone modification is the amino acids in histones being modified and changing the shape of the amino acid
methylation
(not a form of histone modification)
these are added to a cytosine in the DNA that are next to guanine (aka CPG sites - Cytosine-Phosphate Guanine)
causes DNA to bind more tightly to histones
block transcription factors from binding to DNA, by inhibiting the binding of transcription factor(s) to DNA
Methyl molecules = mute =tags on DNA (cytosine) =tightly wound gene = turns gene off
how are genes switched off?
RNA polymerase is blocked by methyl molecules that bind directly to the DNA by attaching to the base cytosine. The methyl molecule causes the DNA to tightly wind around its histones. The gene is considered turned off.
how are genes switched on?
Acetyl molecules bind to histones . The addition of these molecules cause the histones to distance themselves from one another. Access is easier when acetyl molecules cause the DNA to be wound more loosely around the histone The gene is considered turned on.
genome
A persons genome is the hereditary information that is encoded in the DNA.
epigenome
Their epigenome is the sum of all the factors that determine when, where and which genes are switched on or expressed. The epigenome helps to control which genes are active in a particular cell and the fire which proteins will be produced. If the epigenome is abnormal, certain cells may be abnormal and it will result in diseases.
epigenetics
(the study of) changes in gene expression that result from the mechanisms other than changes in the genes that is in the DNA or the genome
factors that affect epigenome
- diet e.g high in fats
- stress
- exposure to pollutants (smoking, chemicals)
- alcohol
how are genetically identical twins not really identical?
epigenetic and environmental differences
how does DNA in a older twin set differ more than it differs in a younger twin set?
Age - more experience, more exposure to the environment, they have differing DNA as their epigenome is different and less similar.
