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What does Chargraff's rule state?
That in DNA, percentages of A and T are the same, and G and C are the same.
What is gene expression?
The process by which DNA directs the synthesis of proteins. The expression of genes that code for protein includes 2 stages: transcription and translation.
Pocket Mouse colour and predation (and peppered moth).
- normally found in sandy deserts, partly covered in black lava
- camouflage provides protection from predation
- colour of species that doesn't camouflage becomes less common
- selection pressures e.g. predators, environment
Were mammoths blonde?
- can isolate DNA from mammoths and compare it to the gene that caused mouse fur to change colour
- found that some mammoths had the light fur gene and some had the dark fur gene
- Genetic make-up of an organism --> 'blueprint'
- genetic information
- detectable properties or traits of an organism
- physical expression of the genotype
Genetic Variation and natural selection are different processes.
genotypic differences lead to...
phenotypic differences which natural selection can act upon
DNA is a macromolecule. What is a macromolecule?
A large polymer, made up of many monomers.
What is the monomer of DNA? and What are its components?
- A nucleotide.
- Components: sugar, a phosphate and a base
The information in DNA is digital with 4 options. What are these 4 options and how is the info stored?
- Adenine, thyamine, Guanine and Cytosine
- The order in which they are arranged is how they information is stored.
Evolution dependes on changes to DNA sequences.
- organisms are selected based on their interaction with the environment
- some of their success is due to genetic variation (inherited traits)
- genotypic differences lead to phenotypic differences which natural selection can act upon
Genetic information is stored in DNA
The three polymers important for genetics
What kind of bonds join monomers together?
Covalent bonds. (strong bonds formed when electrons are shared between two atoms.)
What is a polypeptide?
A polymer (chain) of man amino acids linked together by peptide bonds.
What is a peptide bond?
The covalent bond between the carboxyl group on one amino acid and the amino group on the next, formed by a dehydration reaction.
What are the two types of nucleic acids?
Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA)
Name the Nitrogenous bases. First Purines then pyramidines.
- Purines: Adenine and Guanine
- Pyramidines: Cytosine, Thyamine and Uracil
Structure of nucleic acids: sugars
Deoxyribose in DNA and Ribose in RNA
What is a eukaryotic cell?
A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles. organisms with eukaryotic cells (protists, plants, fungi and animals) are called eukaryotes.
What is a polynucleotide?
A polymer consisting of many nucleotide monomers in a chain; nucleotides can be those of DNA or RNA
What is a nucleic acid?
a polymer consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular activities. The two types are DNA and RNA.
A nucleotide is composed of three parts:
A nitrogenous base (A T G C), a five-carbon sugar (pentose) and a phosphate group.
What is a nucleoside?
the portion of the unit nucleotide, without the phosphate group.
- six-membered ring of carbon and nitrogen atoms
- Cytosine, thyamine and uracil
- smaller than purines
- six membered ring fused to a five membered ring
- larger than pyrimidines
- adenine and guanine
Thyamine is found only in ___ and uracil found only in ___
The sugar connected to the nitrogenous base is ___ in the nucleotides of RNA and _______ in DNA.
how are nucleotides linked together to build a polynucleotide?
- phosphodiester bonds
- consists of a phosphate group that links the sugars of two nucleotides
- this bonding results in a backbone with a repeating pattern of sugar-phosphate units.
The two free ends of the polynucleotide are distinctly different from each other. Explain how:
one end has a phosphate attached to a 5' carbon, and the other end has a hydroxyl group on a 3' carbon
the linear order of bases in a gene specifies the amino acid sequence - the primary structure- of a protein, which in turn specifies that
protein's three-dimensional structure and function in the cell.
Which way do the two phosphate backbones run in a DNA double helix
- opposite directions from each other
- 5' --> 3'
- 'antiparallel' like a divided highway
the strands of dna are called
The strands of DNA in a double helix are held together by what kind of bonds between ______
- hydrogen bonds between the paired bases
- vanderwaals forces between the stacked bases
One long dna double helix includes many genes, each one a particular segment of the molecule
adenine always pairs with
guanine always pairs with
What feature of DNA makes possible the precise copying of genes that is responsible for inheritance?
the fact that the two strands of the double helix are complementary
we should expect two species that appear to be closely related based on fossil and anatomical evidence to also share a greater proportion of their DNA and protein sequences than do more distantly related species. e.g....
the comparison of a polypeptide chain of human hemoglobin with the corresponding hemoglobin polypeptide in five other vertebrates. In this chain of 146 amino acids, humans and gorillas differ in just 1 amino acid, while humans and frogs differ in 67 amino acids
Hersey and Chase concluded that...
the phage DNA entered bacterial cells, but phage proteins did not. They concluded that DNA, not protein, functions as the genetic material of phage T2.
Why can A only pair with T? and G only with C?
- Because the diameter of the double helix allows for only purines to be paired with pyrimidines
- if pyrimidines are paired with pyrimidines, the diameter is too narrow, and vice versaw with purines
- also, adenine can form two hydrogen bonds with thyamine and only thiamine
- guanine forms three hydrogen bonds with cytosine and only cytosine.
DNA, RNA and Protein. Name the monomers of these polymers and the bonds that connect the monomers.
Information in DNA and protein is digital according to...
the order of nitrogenous bases and amino acids
Genetic variation occurs as a result of....
change to the biological information. i.e. changes to the sequences of monomers in a polymer
- are weak bonds
- occur between an electronegative atom (usually nitrogen, oxygen or fluorine) and hydrogen
- 5 prime
- has a phosphate group attached to it
- 3 prime
- has a hydroxyl group attached to it
What is the link between genotype and phenotype?
Proteins (enzymes) are the products of...
What are alleles?
Alternative versions of genes that produce different phenotypes
Examples of proteins in the human body...
- bacteria - help defend body against bacteria/viruses
- muscle proteins actin and mysoin enable muscle movement
- hemoglobin in the blood - oxygen carrier
An RNA molecule usually consists of a single strand.
What is transcription?
- The synthesis of RNA under the direction of DNA
- information is transcribed/copied from one molecule to the other
What is messenger RNA (mRNA)?
A type of RNA molecule that carries a genetic message from the DNA to the protein-synthesizing machinery of the cell
What is translation?
- Translation is the synthesis of a polypeptide, which occurs under the direction of mRNA
- During this stage, there is a change in language: the cell must translate the base sequence of an mRNA molecule into the amino acid sequence of a polypeptide.
- The sites of translation are ribosomes
What are ribosomes?
- Site of translation
- complex particles that facilitate the orderly linking of amino acids into polypeptide chains
The basic mechanics of transcription and translation are similar for bacteria and eukaryotes, but there is an important difference in the flow of genetic information within the cells...what is it?
- Because bacteria do not have nuclei, their DNA is not segregated from ribosomes.
- In a eukaryotic cell, the nuclear envelope separates transcription from translation in space and time.
What is a codon?
- A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.
- written in the 5' to 3' direction
What does the codon AUG do?
it stand for the amino acid methionine and is a 'start' signal for ribosomes to begin translating the mRNA at that point
How many codons function as 'stop' signals, marking the end of a genetic message?
What is the template strand?
- The one of the two DNA strands that is transcribed for each gene.
- It is called the template strand because it provides the pattern, or template for the sequence of nucleotides in an RNA transcript
What is RNA polymerase?
An enzyme that links ribonucleotides into a growing RNA chain during transcription.
What is a mutation?
A change in the nucleotide sequence of an organism's DNA, ultimately creating genetic diversity. Mutations also can occur in the DNA or RNA of a virus.
Beadle and Tatums experiment: linking mutants to the enzyme pathway.
If an organism can't convert one particular compound to another, it presumably lacks an enzyme required for the conversion, and the mutation is in the gene that codes for that enzyme (or protein)
What is the central dogma of molecular biology?
DNA to RNA to Protein
What does the promoter determine?
- which dna strand will be the template strand
- where transcription starts
- serves as a binding site for rna polymerase
What is a transcription unit?
the stretch of DNA that is transcribed into an RNA molecule
the end of protein synthesis triggered by a stop codon which binds release factor that causes the polypeptide to release from the ribosome
a change in gene sequence that, due to the redundancy of the genetic code, has no effect on the amino acid produced, and thus no effect on the phenotype.
Compare DNA polymerase and RNA polymerase in terms of how they function, the requirement for a template and primer, the direction of synthesis and the type of nucleotides used
- both assemble nucleic acid chains from monomer nucleotides whose order is determined by complementary base pairing to a template strand
- both synthesize in the 5' to 3' direction, antiparallel to the template
- dna polymerase requires a primer but RNA polymerase can start a nucleotide chain from scratch
- dna polymerase uses nucleotides with the sugar deoxyribose and the base T, whereas RNA polymerase uses nucleotides with the sugar ribose and the base U
What is a promoter and is it located at the upstream or downstream end of a transcription unit?
The promoter is the region of DNA to which RNA polymerase binds to begin transcription, and it is at the upstream end of the gene.
What makes RNA polymerase start transcribing a gene at the right place on the DNA in a bacterial cell? in a eukaryotic cell?
- In a bacterial cell, RNA polymerase recognizes the gene's promoter and binds to it.
- in a eukaryotic cell, transcription factors mediate the binding of RNA polymerase to the promoter
What is primase?
an enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template
What is a primer?
a short stretch of RNA with a free 3' end, bound by complementary base pairing to the emplate strand that is elongated with dna nucleotides during rna replication
What is a gene?
A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA
What is a species?
A population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not viable, fertile offspring with other such groups.
Which two DNA polymerase play major roles in DNA replication?
DNA polymerase III and DNA polymerase I
features of the genetic code
- degenerate but unambiguous
- non overlapping
- start and stop codons
conversion of a base sequence to an amino acid sequence requires a....
an adaptor molecule called tRNA
structure of a tRNA molecule
two step decoding process of translation:
- Amino acid is attached to the corresponding tRNA by aminoacyl tRNA synthetase
- Codon/anticodon interaction
tRNA molecules with an amino acid bound are said to be...
charged, or activated
protein synthesis is cataylsed by the...
what do ribosome subunits consist of?
rRNA and proteins
Protein synthesis on the ribosome:
- Using information from a template mRNA
- Amino acids are linked by covalent bonds
- Protein grows in one direction only
- Amino acids added to C terminus
- Energy requiring
The ribosome has two binding sites for tRNA molecules:
- The A (amino acyl) site -The next amino acid/tRNA waits for peptide bond formation
- The P (peptidyl) site -Holds the growing protein attached to a tRNA
3 steps of protein synthesis:
after RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand
the polymerase moves downstream, unwinding the DNA and elongating the RNA transcript 5' to 3'. in the wake of transcription, the DNA strands re-form a double helix.
Eventually the RNA transcript is released and the polymerase detaches from the DNA.
Initiation of protein synthesis...
- Identification of the AUG start codon
- Insertion of the first charged tRNA, the initiator tRNA
- Assembly of the ribosome
- The small ribosomal subunit interacts with mRNA, and the initiator tRNA
- When the large subunit attaches, the Met-tRNA is in the P site
- A three step cycle:
- Entry of tRNA into the A site
- Formation of peptide bond by peptidyl transferase
- Translocation (movement of the ribosome by one codon)
- The mRNA is translated 5' to 3'
transcription and translation are ______ steps
- one gene, many mRNAs, more proteins
- no nucleus,
- transcription and translation in the same compartment
- transcription in nucleus
- translation in cytoplasm
What is a mutation?
- A heritable change in DNA sequence
- mutations occur at random
what do mutations occur as a result of?
- exposure to radiation or chemicals, e.g. uv light and x rays, cigarette smoke burnt meat
- a result of DNA replication errors, ie replication not 100 per cent accurate
are mutations random? is natural selection random?
the base change does not result in a protein change
a single amino acid is changed
- an amino acid codon is changed to a stop codon
- up to one third of genetic diseases are caused by nonsense mutations
- some drugs cause the ribosome to read through the stop codon
in sickle cell anaemia, genotype determines phenotype:
shape of blood cell, disc or sickle shape
- nucleotides are inserted or deleted, resulting in the loss of the normal reading frame
- insertion/deletion is not a multiple of 3
- Mutations in genes cause enzymes to become dysfunctional, leading to disease (sickle cell anaemia)
- Mutations in genes sometimes improve function, (Belgian blue cattle and mighty mouse)
- Mutations can occur in non-coding DNA and have phenotypic effects by altering regulation of genes eg promoter mutations
- Mutations may have little or no effect on phenotype
- Mutations are the raw material for evolution
how do genotypes determine phenotype? (summary)
- The roles of DNA, RNA and protein in he expression of genetic information
- Transcription (RNA synthesis)
- Translation (protein synthesis)
- The genetic code
- Mutations and their phenotypic effects
differentialy regulated proteins??
made only when needed
made all the time
where does gene regulation occur?
- transcription (most common)
- protein activity
lactose intolerance is due to lack of which enzyme?
why is gene regulation important?
- Regulation is important in development and in responding to environmental change
- Genes are controlled by genetic switches that turn them on and off.
what do we need for a genetic switch?
A mechanism by which the rate of transcription can be altered
A mechanism for sensing the environment
describing the mRNA that encodes for multiple different polypeptides
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