Genetics Flashcards
DNA is a polynucleotide, what does this mean?
It’s made up of lots of nucleotides joined together
DNA is made of nucleotides that contain which 3 components
Pentose Sugar
Phosphate group
Nitrogenous base
Lots of nucleotides joined together is called a….
Polynucleotide
The sugar in DNA molecules is….
A deoxyribose sugar
Each nucleotide has the same….
Sugar and phosophate, the base on each nucleotide can vary
What are the four nitrogenous bases
Adenine
Quanine
Thymine
Cytosine
2 polynucleotide strands join together to form…
A double helix
How is a double helix formed
Nucleotides join up between the phosphate group of one nucleotide and the sugar of another, creating a sugar-phosphate backbone. 2 DNA polynucleotide strands join together by hydrogen bonding between bases, each base can only join with one partner= specific base pairing (A-T) (G-C). The two strands wind up to form the DNA double helix
Genes code for….
Proteins, they contain the instructions to make them. Proteins are made from amino acids, different proteins have different number and order of amino acids. It’s the order of the nucleotide bases in a gene that determines the order of amino acids in a particular protein. Each amino acid is coded for by a sequence of 3 bases in a gene. A DNA triplet is also called a base triplet or codon. Different sequences of bases code for different amino acids, called the genetic code. So the sequence of bases in a section of DNA is a template that’s used to make protein during protein synthesis
DNA is copied into RNA for protein synthesis. explain
DNA molecules are found in nucleus, but organelles for protein synthesis (ribosomes) are found in cytoplasm. DNA= too large to move out of nucleus, so section copied into RNA. Process called transcription. RNA leaves nucleus and joins with a ribosome in cytoplasm where it can be used to synthesise a protein. Process called translation
How does RNA differ from DNA
The sugar in RNA is ribose sugar
The nucleotides form a single polynucleotide strand
Uracil replaces thymine as a base, pairs with adenine
What are the two different types of RNA
Messengers RNA (mRNA)
Transfer RNA (tRNA)
What is mRNA
A single polynucleotide strand, groups of 3 adjacent bases usually called codons. mRNA is made in nucleus during transcription. Carries genetic code from DNA in nucleus to cytoplasm where it’s used to make a protein during translation
What is tRNA
A single poly nucleotide strand folded int a clover shape. Hydrogen bonds between specific base pairs hold molecule in shape. Every tRNA molecule has a specific sequence of 3 bases at one end called an anticodon. They also have an amino acid binding site at the other end. tRNA found in cytoplasm where it’s involved in translation. It carries amino acids that are used to make proteins to the ribosomes
What is the first stage of protein synthesis
Transcription
What is the second stage of protein synthesis
Translation
mRNA is edited in eukaryotic cells. Explain
Genes in eukaryotic DNA contain sections that dont code for amino acids, called introns. The bits that do code called exons. During transcription the introns and exons both copied into mRNA. mRNA strands containing introns and exons called pre-mRNA. Introns removed from pre-mRNA strands by process called splicing ( introns are removed and exons joined forming mRNA strands. Takes place in nucleus. mRNA then leaves nucleus for next stage (translation)
3 features of the genetic code
Non overlapping
Degenerate
Universal
Define genetic code
Sequence of bases triplets (codons) in mRNA which code for specific amino acids
Transcriptional factors control what
The transcription of target genes
What are mutations
Changes to the base sequence of DNA
What can mutations be caused by
Errors during DNA replication
Mutagenic agents
What do mutagenic agents do
Increase rate of mutation
Examples of some mutagenic agents
UV radiation, ionising radiation, some chemicals and viruses
How do mutagenic agents work
Act as base- chemicals called base analogs can substitute for a base during DNA replication, changing base sequence in new DNA
Altering bases- some chemicals can delete or alter bases
Changing structure of DNA- some types of radiation can change structure of DNA which causes problems during DNA replication
Genetic disorders and cancer are caused by…
Mutations
What are stem cells
Unspecialised cells that can develop into other types of cell
Where are stem cells found
In embryo and some adult tissues
What are totipotent cells
Stems cells that mature into any type of body cell in an organism
Only present in the early life of an embryo
What are multipotent cells
The few stem cells that remain in mature animals
They can only develop into few types of cells
Plants contain totipotent stem cells. Explain
Mature plants also have stem cells, found in areas where plant is growing eg roots and shoots. All stem cells in plants are totipotent which means they can be used to grow plant organs eg roots or whole plants IN VITRO (artificially). Growing plant tissue artificially is called tissue culture
What is tissue culture
Growing plant tissue artificially
Totipotent and multipotent stem cells can be used in treating some genetic disorders. Explain
As they can develop into any other cell type, they could be used to replace cells damaged by illness or injury. Some stem cell therapies already exist for some diseases affecting the blood and immune system. Bone marrow contains stem cells that can become specialised to form any blood cell. Bone marrow transplants can be used to replace the faulty bone marrow in patients that produce abnormal blood cells, the stem cells in the transplanted bone marrow divide and specialise to produce healthy blood cells. Used to treat leukaemia and lymphoma, sickle cell anaemia and SCID
How do stem cells become specialised
During their development they only transcribe and translate part of their DNA
Benefits to using stem cells in medicine
Could save many lives eg many people waiting for organ transplants die before donor organ available. Stem cells could be used to grow organs for those people awaiting transplants
Could improve quality of life eg stem cells could be used to replace damaged cells in eyes of blind people
What are the ethical issues surrounding stem cell use
Procedure results in destruction of an embryo that could become a foetus if placed in a womb. Some believe that at the moment of fertilisation an individual is formed that has right to live and it’s wrong to destroy it. Some people think scientists should only use adult stem cells as then no embryos are destroyed, but these can’t develop into as many different specialised cells as embryonic stem cells.
What do hereditary mutations cause
Cancer and genetic disorders
Example of specialised cell
Red blood cell
Info on red blood cell as specialised cell
Produced in type of stem cell called bone marrow. Contains large amount of haemoglobin, no nucleus. Stem cell produces new cell in which genes for haemoglobin production is switched on, along with the gene involved in removing the nucleus. Other genes expressed and switch off= specialised cell
How is a single totipotent cell used to grow plants
Single totipotent cell removed from growing region of plant eg root or shoot
Cell placed in growth medium (agar) which contains nutrients and growth factors. Agar is sterile so microorganisms can’t grow and compete with plant cells
Stem cell grows, divides into mass of unspecialised cells. If conditions suitable (eg cells given right growth factors) cells mature into specialised cells
Cells grow and specialise to form plant organ or entire plant depending on growth factors used
Bone marrow contains stem cells that become specialised to form…
Any type of blood cell
Example of stem cell therapies
Bone marrow transplants- used to replace the faulty bone marrow in patients that produce abnormal blood cells. The stem cells in the transplanted bone marrow divide and specialise to produce healthy blood cells. Technique is successful in treating leukaemia and lymphoma. Also used to treat genetic disorders such as sickle cell anaemia and severe combined immunodeficiency (SCID)
What is SCID
Affects immune system, poorly functions due to defective white blood cells. These cells can’t defend the body against infections by identifying and destroying microorganisms. Sufferers extremely susceptible to infections. Bone marrow transplant replaces faulty bone marrow with donor marrow that contains stem cells without faulty genes that cause SCID. These differentiate to produce functional white blood cells which can identify and destroy pathogens= immune system functions properly
Scientists are researching the use of stem cells as treatment for many conditions including…
Spinal cord injuries- stem cells used to replace damaged nerve tissue
Heart disease and damage caused by heart attacks- stem cells used to replace damaged heart tissue
Bladder conditions- stem cells used to grow whole bladders, which are then implanted in patients to replace diseased ones
Respiratory diseases- donated windpipes stripped down to their simple collagen structure, then covered with tissue generated from stem cells. Then transplanted into patients
Organ transplants- organs grown from stem cells to provide new organs for people on donor waiting lists
What are introns
Non coding sections of DNA. doesn’t code for amino acids
What are exons
Coding sections of DNA , does code for amino acids
Give 2 characteristic features of stem cells
They replicate/ replace themselves
Can differentiate into any type of cell
Explain why the percentage of bases from the middle part of the chromosome and the end part are different
Different genes which have different base sequences
What are genetic disorders
Inherited disorders caused by abnormal genes or chromosomes eg cystic fibrosis
What are acquired mutations
Mutations that occur in individual cells after fertilisation (eg in adulthood)
What is a tumour
A mass of abnormal cells
What is a cancer
A tumour that invades and destroys surrounding tissue
What are the 2 types of gene that control cell division
Tumour suppressor genes
Proto oncogenes
Tumour suppressor gene info
Control cell division
Can be inactivated if a mutation occurs in the DNA base sequence. When functioning normally they slow cell division by producing proteins which stop cells dividing or cause them to self-destruct. If mutation occurs, protein isn’t produced. Cells divide uncontrollably, results in tumour
Proto-oncogenes info
The effect of proto-oncogenes can be increased if a mutation occurs in the DNA base sequence. A mutated proto-oncogene= oncogene. When functioning normally they stimulate cell division by producing proteins that make cells divide. If mutation occurs, the gene becomes overactive. Stimulates cells to divide uncontrollably= tumour
What is a codon
A sequence of 3 bases on mRNA or DNA, which code for a specific amino acid
Why is the genetic code described as being universal
In all organisms, the same triplet codes for the same amino acid
What is the maximum number of different DNA triplets that can be made from the four bases
64
What is a transcription factor
Protein that moves from cytoplasm to DNA and binds to a specific part of DNA/specific promoter
It either leads to or prevents the mRNA production by allowing or blocking RNA polymerase to work
