Genetics Flashcards
What are nucleotides
Nitrogen-containing organic substances that form the base of the nucleic acids DNA and RNA.
What do all nucleotides contain (3)
- A phosphate group
- A pentose sugar
- A nitrogen containing base
How to draw a nucleotide
House - pentagon (Pentose sugar) , garage - rectangle (nitrogenous base), satellite dish - circle (phosphate group)
What are the sugars made of in DNA and RNA
DNA - deoxyribose
RNA - ribose
What are the four nitrogenous bases
- Adenine
- Thymine
- Cytosine
- Guarnine
How do the nitrogenous bases pair
Adenine + Thymine
Cytosine + Guanine
Apple tart + chocolate gâteau
What is deoxyribonucleic acid
The hereditary code in living organisms
What does deoxyribonucleic acid consist of
The four nitrogenous bases
What is the definition of a gene
A section of DNA which codes for a particular protein
What is the central dogma
The idea of how protein is synthesised from DNA
How does RNA differ to DNA
- Single stranded
- Has ribose not deoxyribose
- Has uracil which is complementary to adenine (it replaces thymine in DNA)
How to draw a GCSE level nucleus
Circle
Add chromosomes
Add some pores
What are the steps of the central dogma (see diagram on nucleotides and DNA note)
- Chromosome
- Transcription
- MRNA takes it out of the nucleus
- Passes through a ribosome (translation) - carried to the ribosome by tRNA
- Becomes a polypeptide
- Becomes the final product e.g. insulin from chromosome 11
What replaces thymine in RNA
Uracil (U)
How do the DNA template base + the transfer RNA anticodon relate to the messenger RNA codon
They are complementary
Name 2 proteins and their functions
- Haemoglobin - carries oxygen throughout the body
- Insulin - to turn food into energy, moving sugar from blood into other tissues for storage
What are polypeptides
Chains of amino acids
How do multiple polypeptides create proteins
They fold up and join with other polypeptides
What is transcription
Making an RNA copy of the DNA sequence. mRNA is formed.
What is translation
Assembling the amino acids in the correct order following the sequence of bases on mRNA
Where does translation occur
Ribosomes
What leaves the nucleus and attaches to the ribosome during translation
mRNA
What is a codon
Every triplet of bases on the messenger RNA
What does tRNA do
Carries amino acids to the ribosome, where they then bond together in the order set out by the mRNA (complementary to the mRNA bases)
What is the full name of tRNA
Transfer RNA
What is the triplet of bases on tRNA called
An anticodon
What does the anticodon on tRNA match with
COMPLEMENTARY (with an E) bases on the codons on the RNA
How is a polypeptide chain formed from amino acids
Ribosomes create bonds
What are the steps of protein synthesis
- mRNA is created from DNA via transcription
- The RNA bases are lined up in the correct order using complEmentary base pairings
- The amino acids are assembled in the correct order via translation
- tRNA carries amino acids to the ribosome
- The ribosome forms bonds between the amino acids to make a polypeptide chain
- The polypeptide folds and joins up with other polypeptides to form a protein
How do you go from DNA template base sequence to mRNA codon
Use the complementary base (U replaces T in RNA)
What does U stand for in RNA
Uracil
What is an allele
An alternative version of a gene e.g. blonde hair, brown hair etc. In this case the gene is hair colour
How many alleles for each gene do we have
2 (1 from each parent)
What is the name for if you get the same allele from each parent
Homozygous (dominant/recessive - depending on if they are both dominant or recessive)
What is it called if you have different alleles from each parent
Heterozygous
Can you have 2 different recessive alleles and why/why not
No - one will always be dominant over another. Eg if this is the dominance order from L-R for eye colour: brown, green, blue. If you get brown and then blue or green, blue or green will be recessive, but if you get blue and green, the green becomes dominant over the blue
What is the phenotype
The observable characteristics of an individual e.g. blue eyes
What is the genotype
The genetic make-up of an individual e.g. ee
Why does the Y chromosome affect the gender
It carries the sex-determining gene, which triggers the development of testes. In the absence of a Y chromosome, ovaries develop.
Which is male and which is female
XX
XY
XX - Female
XY - Male
When using letters for alleles, which two letters must you never use and why
X and Y - it is well known that X and Y are the sex-determining genes
What is a punit grid
A grid to show the likelihood of each possible allele combination for offspring (see Inheritance note for diagram please)
Does a dominant allele produce the same phenotype in heterozygotes and homozygotes
Yes
Are dominant or recessive usually upper or lower case
Dominant = upper
Recessive = lower
What is a good way to give a letter for alleles of a gene
The letter that makes sense (eg for eye colour it would be e)
Then E for dominant and e for recessive
How many chromosomes does a human body cell have
46 (23 pairs)
What are the four stages of mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
What is a haploid cell and give some examples
Only one copy of every chromosome so only 23. Sperm and egg only
What is mitosis
A diploid cell (46) splitting into 2 diploid cells
How many chromosomes does a diploid cell have and give an example of a diploid cell
46 - all body cells except sperm and egg
What is meiosis
A diploid cell splits into 2 diploid cells, which both split into 2 haploid cells each (so you end up with 4 haploid cells)
When does mitosis occur
During growth, repair, cloning and asexual reproduction
Name 6 differences between mitosis and meiosis
- Mitosis ends diploid, meiosis ends haploid
- Mitosis somatic cells (not sex cells) meiosis sex cells
- Mitosis divides into 2 cells, meiosis divides into 4 cells
- Mitosis asexual reproduction, meiosis sexual reproduction
- Mitosis produces genetically identical cells, but meiosis doesnt produce genetically identical cells
- Mitosis 1 round of division, meiosis 2 rounds
What steps does meiosis consist of
One step of DNA replication followed by 2 cell divisions
What are somatic cells
Cells that are not used in reproduction
What are mutations
Mistakes in the DNA sequence
What happens to the DNA sequence in the event of a mutation
The DNA sequence is changed
Do all mutations cause change and why
No - the same amino acid can be coded for
What happens if the mutation causes the protein made to change
Consequences - good or bad, big or small
What causes mutations
They can be random or caused by mutagens
Name 4 mutagens
- Cigarette smoke
- X-rays
- Asbestos
- Radiation
What is the definition of differentiation
Processes taking place during the development of an embryo, where cells become specialised to carry out specific functions
Where does differentiation start from
Stem cells that become specialised e.g. red blood cells
When can cell differentiation occur
Any time in life, not just when you are an embryo
What are stem cells
Cells that can divide by mitosis but have not been differentiated
Can stem cells differentiate into specialised cells
Yes
How do stem cells differentiate into specialised cells
They regulate the expression of genes in the cell. Some genes are “switched on” whilst others are “switched off”, which means that cells produce some proteins but not others, eventually leading to the development of a particular type of cell
What can stem cells be used to do
Replace damaged or malfunctioning cells
Name 2 things stem cells can be used to cure and how
Blindness (making new retinal cells)
Diabetes (making new pancreatic cells to secrete insulin)
Where are stem cells found
In the developing embryo and in adult tissues (e.g. skin and bone marrow)
Can stem cells found found in adults e.g in bone marrow differentiate into anything
No - bone marrow stem cells can only differentiate into blood cells (they are called haematopoietic)
What happens to mRNA
It forms a template for the tRNA to place the amino acids in to ensure that the correct protein is formed, then it breaks down.
