Unit 1 - Let’s Achieve Flashcards
Somatic cells
A somatic cell is any cell in the body other than cells involved in reproduction.
Somatic stem cells divide by mitosis to form more somatic cells.
Germline cells
Germline cells are gametes (sperm and ova) and the stem cells that divide to form gametes.
Germline stem cells division
Germline stem cells divide by mitosis and meiosis.
Division by Mitosis produces more germline stem cells.
Division by Meiosis produces haploid gametes.
Germline stem cells - mitosis
The nucleus of a germline stem cell can divide by mitosis to maintains the diploid chromosome number.
Diploid cells
Diploid cells have twenty-three homologous chromosomes.
Germline stem cells - meiosis
The nucleus of a germline stem cell can divide by meiosis to produces haploid gametes.
It undergoes two divisions, firstly separating homologous chromosomes and secondly separating chromatids.
Haploid gametes
A haploid gamete contains twenty-three single chromosomes.
Cellular differentiation
Cellular differentiation is the process by which a cell expresses certain genes to produce proteins characteristic for that type of cell. This allows the cell to carry out specialised functions.
Embryonic stem cells
Cells in an early embryo can differentiate into all cell types that make up the organism.
All the genes in an embryonic stem cell can be switched on, so these types of cells can differentiate into any cell type and are said to be pluripotent.
Tissue stem cells
Tissue stem cells are involved in the growth, repair and renewal of cells found in a particular tissue.
Tissue stem cells are multipotent as they can differentiate into all the types of cell found in a particular tissue type.
E,g. Ref blood cells from bone marrow
Applications of stem cells - therapeutic
The therapeutic uses of stem cells involve the repair of damaged or diseased organs or tissues. Under the right conditions, in the laboratory, embryonic stem cells can self-renew.
Examples are the use in corneal repair and the regeneration of damaged skin.
Applications of stem cells - research
Stem cell research provides information on cell processes such as cell growth, differentiation and gene regulation.
Stem cells are used as model cells to study how diseases develop or being used in drug testing.
Applications of stem cells - ethical issues
Use of embryonic stem cells can offer effective treatments for disease and injury; however, it involves the destruction of embryos.
Cancer cells
Cancer cells divide excessively because they do not respond to regulatory signals. This results in a mass of abnormal cells called a tumour.
Secondary Tumor
Cells within the tumour may fail to attach to each other, spreading the body where they may form secondary tumours.
DNA
DNA is a double helix and consists of 2 long chains (a polymer) of subunits called nucleotides (monomers).
Nucleotides
A nucleotide consists of three main components:
Deoxyribose sugar
Phosphate
Nitrogenous base
The four nitrogenous bases are Adenine, Thymine, Guanine and Cytosine.
Nucleotides bonding
The phosphate group bonds to the 5’ (5 prime) carbon of the sugar. The 3’ carbon is exposed on the bottom of the pentagon.
Backbone of DNA
The components of a nucleotide that make up the backbone of DNA are the sugar-phosphate groups. The backbone is known as the sugar-phosphate backbone.
Bonding between bases
Weak Hydrogen bonds form between complementary base pairs
Antiparallel strands
DNA strands have the phosphate group exposed on the 5’ and the deoxyribose sugar exposed on the 3’.
One strand runs in a 5’ to 3’ direction, whilst the opposite strand runs in 3’ to 5’ direction. This is an antiparallel structure forming the double helix.
What forms the Genetic code
The sequence of bases on DNA forms the genetic code.
When does DNA replication occur
DNA replication occurs prior to cell division.
DNA requirements
DNA replication requires the use of ATP, free DNA nucleotides and other enzymes throughout the process.
What enzyme replicates DNA
DNA polymerase is the enzyme that replicates DNA.
What does DNA polymerase require to start
DNA polymerase requires a primer to start DNA replication.
Primer
A primer is a short strand of nucleotides which binds to the 3’ end of the template (parent/original) DNA strand. This allows DNA polymerase to add new nucleotides.
Process of DNA replication
DNA is unwound and hydrogen bonds between bases are broken – forming two template strands.
Primer attaches to a short sequence on the DNA allowing DNA polymerase to bind.
DNA polymerase will add nucleotides using the complementary base pairing rule to the deoxyribose (3’) end of the new strand which is forming.
Replication of leading strand of DNA
DNA polymerase works in a 5’ to 3’ direction. DNA polymerase can only add nucleotides to the 3’end of the growing strand. This means that one strand is replicated continuously, and we call this the leading strand.
Replication of lagging strand of DNA
Due to the antiparallel structure of DNA the fact that DNA polymerase can only add nucleotides onto the 3’end, the opposite strand has to be replicated in fragments. This is known as the lagging strand. This requires the use of many primers and the fragments produced are joined together by the enzyme ligase.
What does PCR amplify
The polymerase chain reaction amplifies DNA using complementary primers for specific target sequences.
What happens in PCR cycle
The polymerase chain reaction consists of repeated cycles of heating and cooling to amplify the target DNA
PCR stages
DNA is heated between 92°C and 98°C to break the hydrogen bonds between bases and separate the two strands.
The DNA is then cooled to between 50°C and 65°C to allow primers to bind to target sequences.
It is then heated to between 70°C and 80°C for heat tolerant DNA polymerase to replicate the region of DNA.
Primers
Primers are short strands of nucleotides which are complementary to specific target sequences at the two ends of the region of DNA to be amplified. The DNA to be amplified will be the sample DNA.
PCR practical applications
Examples of the practical applications of PCR are to help solve crimes, settle paternity suits and diagnose genetic disorders.
Gene expression
Gene expression involves the transcription and translation of DNA sequences. Only a fraction of genes in the cell are expressed.
RNA
RNA is a single stranded and is composed of RNA nucleotides.
RNA nucleotides
RNA nucleotides consist of a phosphate group, ribose sugar and one of four nitrogenous bases. Adenine, Uracil, Guanine and Cytosine.
3 types of RNA
mRNA
tRNA
rRNA
mRNA
mRNA carries a complimentary copy of the DNA code from the nucleus to the ribosome. mRNA is transcribed from DNA in the nucleus and translated into proteins in the cytoplasm.
Codon
Each triplet of bases on mRNA is known as a codon and codes for 1 specific amino acid.
tRNA & anticodons
Transfer RNA (tRNA) folds due to complementary base pairing.
tRNA has a triplet of bases exposed known as an anticodon at one end of the tRNA molecule.
At the other end of the tRNA molecule is the specific amino acid attachment site. The tRNA molecule carries its specific amino acid to the ribosome.
rRNA function
rRNA and proteins form the ribosome.
Transcription process / stages
The enzyme RNA polymerase moves along DNA, unwinding the double helix and breaking the hydrogen bonds between the bases thereby unzipping the double helix.
As RNA polymerase breaks the bonds, it synthesises a primary transcript of mRNA on the DNA template strand using free RNA nucleotides. These RNA nucleotides form hydrogen bonds with the exposed DNA bases by complementary base pairing.
Uracil is the complementary base pair to adenine.
A primary mRNA transcript is formed.
RNA splicing
During RNA splicing non-coding regions known as introns are removed from the primary transcript and the coding regions called exons remain and are spliced together.
The exons when spliced together form a mature (mRNA) transcript.
during the process of splicing the order of the exons remains unchanged.
Translation process - mRNA leaving nucleus
The mRNA mature transcript leaves the nucleus through a nucleur pore to the ribosome for the process of translation into a polypeptide.
Where does translation begin and end
Translation starts at a START codon and ends at a STOP codon. This is very important to ensure the entire polypeptide chain is produced without any amino acids missing.
Translation process ?
Translation is the synthesis of a polypeptide chain under the direction of mRNA at the ribosome.
Translation begins at a start codon and ends at a stop codon.
The mRNA mature transcript leaves the nucleus through a nucleur pore to the ribosome for the process of translation into a polypeptide.
Each tRNA leaves the ribosome (after being joined together by peptide bonds) as the polypeptide is formed.
The ribosome exposes one codon on the mRNA allowing tRNA to bring a specific amino acid to the ribosome. The correct anticodon on the tRNA will complementary base pair with the codon on the mRNA, bringing the correct specific amino acid with it. The ribosome exposes the next codon where another tRNA and its amino acid will complementary base pair with that codon.
What joins amino acids together
Aligning amino acids are joined together by a peptide bond, allowing the tRNA to leave the ribosome as the polypeptide is formed. This happens throughout the length of the mRNA until it reaches a STOP codon.
Alternative splicing process
Different proteins can be expressed from one gene as a result of alternative RNA splicing.
Different mature mRNA transcripts are produced from the same primary transcript depending on which exons are retained.
What bond amino acids bond to form?
Amino acids are bonded together by peptide bonds to form polypeptide chains.
What do polypeptide chains fold to make
Polypeptide chains fold to form the three-dimensional shape of a protein, held together by hydrogen bonds and other interactions between individual amino acids.
Protein shapes
Proteins have a large variety of shapes which determines their functions.
Phenotype
a phenotype is a physical expression of a gene/characteristic. This is determined by the protein produced as a result of gene expression.
Environmental factors can also influence phenotype.
Mutations
Mutations are changes in DNA that can result in no protein or altered protein being synthesised.
Single gene mutations
Single gene mutations involve the alteration of a DNA nucleotide sequence as a result of:
- the substitution of nucleotides
- insertion of nucleotides.
- deletion of nucleotides.
Missense mutation
Missense mutations – result in one amino acid being changed for another. This may result in a non-functional protein or may have little effect on the protein depending on the amino acid that has been changed.
Example Sickle cell disease.
Nonsense mutations
Nonsense mutations result in premature stop codon being produced which results in a shorter protein.
Example Duchenne Muscular dystrophy.
Splice site mutation
Splice site mutations result in some introns being retained and/or some exons not being included in the mature transcript.
Example beta thalassemia.
What causes frame shift mutation
The effect of an insertion or deletion of a nucleotide results in frame shift mutations.
What do frame shift mutations cause
Frame shift mutations cause all of the codons and all of the amino acids after the mutation to be changed.
This has a major effect on the structure of the protein produced.
Chromosome mutation types
Duplication
Deletion
Inversion
Translocation
Chromosome mutation - duplication
Duplication – a section of a chromosome is added from its homologous partner.
Chromosome mutation - deletion
Deletion is where a section of the chromosome is removed.
Chromosome mutation - inversion
Inversion is where a section chromosome is reversed.
Chromosome mutation - translocation
Translocation is where a section of a chromosome is added to a chromosome, not its homologous partner.
What can chromosome mutations lead to
The substantial changes in chromosome mutations often make them lethal.
Genome
The genome of the organism is its entire hereditary information encoded in DNA.
The genome is made up of genes and other DNA sequences that do not code for proteins
Genomic sequencing
In genomic sequencing the sequencing of nucleotide bases can be determined for individual genes and entire genomes.
Genomic sequencing- computer programmes
Computer programmes can be used to identify base sequences by looking for the sequences similar to known genes
Comparing individuals genomes
To compare genomes from individuals this requires:
sequence data
computer and statistical analyses (bioinformatics)
How can an individuals genome be used
- can be analysed to predict the likelihood of developing certain diseases.
- can also be used to select the most effective drugs and dosage to treat their disease (personalised medicine).
Pharmacogenetics
Pharmacogenetics is the use of genome information in the choice of drugs.
Metabolic pathways
Metabolic pathways are integrated and controlled pathways of enzyme- catalysed reactions within a cell.
Metabolic pathways steps
Metabolic pathways can have reversible, irreversible and alternative routes.
Anabolic pathways
Anabolic reactions involve the building up of large molecules from small molecules and require energy
Catabolic pathways
Catabolic reactions breakdown large molecules into smaller molecules and release energy.
Functions of proteins within membranes
Proteins in the membrane act as:
Pores (allowing molecules to pass through)
Pumps (allowing molecules to pass through the membrane, however this requires energy – so the molecule is actively pumped inside or outside of the cell.)
Enzymes (catalysing chemical reactions)
What controls metabolic pathways
Metabolic pathways are controlled by the presence or absence of key enzymes.
Factors affecting rate of metabolic pathways
Factors that control the rate of enzyme activity such as temperature, pH, substrate concentration and inhibition will also regulate the rate of a metabolic pathway.
Induced fit
When a substate binds to the active site, the active site will change shape. This is to allow the active site to better fit the substrate after the substrate binds. This is known as the induced fit.
Activation energy
All chemical reactions require activation energy which needs to be overcome to get them started.
It is the minimum energy required for a reaction to take place
Active site - molecules
By having the active site hold molecules in a particular orientation this allow bonds to made or broken easily. The activation energy is therefore lowered. With the addition of the enzyme, not as much energy is needed to allow the reaction to commence.
Substrate mooecules affinity
Substrate molecules have high affinity for the active site which allows the substrate to bind easily.
Product molecules affinity
Product molecules have a low affinity for the active site, and this allows the product(s) to leave the active site and allows the active site to bind again with another substrate molecule.
Reversible metabolic pathways
Some metabolic pathways are reversible and the presence of a substrate or the removal of a product will drive a sequence of reactions in a particular direction.
Competitive inhibitors
Competitive inhibitors bind at the active site preventing the substrate from binding. Competitive inhibition can be reversed by increasing the substrate concentration
Non-competitive inhibitors
Non-competitive inhibitors bind away from the active site but change the shape of the active site preventing the substrate from binding. This type of inhibition cannot be reversed by increasing the substrate concentration.
Feedback inhibition
Feedback inhibition occurs when the end-product in the metabolic pathway reaches critical concentration. The end-product inhibits an earlier enzyme, blocking the pathway, and so prevents further synthesis of the end product.
Aerobic respiration pathways
The three pathways of aerobic respiration are:
Glycolysis
Citric acid Cycle
Electron transport chain
Glycolysis
Glycolysis is one of the three main pathways of aerobic respiration and involves the breakdown of glucose to pyruvate.
Glycolysis ATP
ATP is required for the phosphorylation of glucose and intermediates during the energy investment phase of glycolysis. (2 ATP)
The leads to the generation of more ATP during the energy pay-off stage (4 ATP) and results in a net gain of ATP (net gain of 2 ATP
Dehydrogenase enzymes
Dehydrogenase enzymes remove hydrogen ions and electrons and pass them to the coenzyme NAD, forming NADH. This occurs in both glycolysis and the citric acid cycle.
The hydrogen ions and electrons from NADH are passed to the electron transport chain on the inner mitochondrial membrane.
Citric acid cycle
The citric acid cycle is one of the three main pathways of aerobic respiration.
In aerobic conditions, pyruvate is converted into an acetyl group that combines with coenzyme A forming acetyl coenzyme A. NADH and carbon dioxide are also formed during this process.
Citric acid cycle process
In the citric cycle, the acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate.
During a series of enzyme-controlled steps, citrate is gradually converted back into back into oxaloacetate which results in the generation on ATP and release of carbon dioxide.
Electron transport chain (consists of?)
The electron transport chain is a series of carrier proteins attached to the inner mitochondrial membrane.
Electron transport stage process
Electrons are passed along the electron transport chain releasing energy.
This energy allows hydrogen ions to be pumped across the inner mitochondrial membrane.
The flow of these ions back through the membrane protein ATP synthase results in the production of ATP.
Finally, the hydrogen ions and electrons combine with oxygen to form water.
Electro transport chain - role of ATP
ATP is used to transfer energy to cellular processes which require energy.
Examples: Nerve transmission, muscle contraction and active transport.
Locations of stages
The locations of the stages within the cell are:
Glycolysis – Cytoplasm
Citric acid cycle – Matrix of the mitochondria
Electron Transport chain – Proteins within the inner mitochondrial membrane (Cristae)
Impact of exercise on muscle cells
Muscle cells during vigorous exercise do not get sufficient oxygen to support the electron transport chain. Under these conditions, pyruvate is converted to lactate.
Production of lactate due to lack of oxygen to support the electron transport chain
When pyruvate is converted into lactate, this involves the transfer of hydrogen ions from the NADH, produced in glycolysis, to pyruvate in order to produce lactate.
This regenerates the NAD needed to maintain ATP production though glycolysis.
Muscle fatigue
As lactate accumulates muscle fatigue occurs.
Oxygen debt
The oxygen debt is repaid when exercise is complete. This allows respiration to provide the energy to convert lactate back to pyruvate and glucose in the liver.
Slow twitch muscles contractions
Slow-twitch muscles fibres contract relatively slowly but can sustain contractions for longer.
Slow twitch muscle uses
They are useful for endurance activities such as long-distance running, cycling or cross-country skiing.
Slow twitch muscle fibres generation of ATP
Slow-twitch muscle fibres rely on aerobic respiration to generate ATP and have many mitochondria, a large blood supply and a high concentration of the oxygen-storing protein myoglobin.
Slow twitch muscle fibres fuel storage
The major storage fuel of slow-twitch muscle fibres is fat.
Fast twitch muscle fibres contactions
Fast-twitch muscle fibres contract relatively quickly, over short periods
Fast twitch muscle fibres uses
They are useful for activities such as sprinting or weightlifting.
Fast twitch muscle fibres generation of ATP
Fast-twitch muscle fibres can generate ATP through glycolysis only and have fewer mitochondria and a lower blood supply compared to slow twitch muscle fibres.
Fast twitch muscle fibres main storage of fuel
The major storage fuel of fast-twitch muscle fibres is glycogen
Patterns of muscle tissue in athletes
Most human tissue contains a mixture of both slow- and fast-twitch muscle fibres.
Athletes show distinct patterns of muscle fibres that reflect their sporting activities.
What is transcription
Transcription is the process by which mRNA is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm.
