SB3 - Genetics Flashcards
What is sexual reproduction?
Involves the joining of male and female gametes
What gametes join together in sexual reproduction of flowering plants?
Pollen & egg cells
How many chromosomes does a normal cell have?
46
How many chromosomes does a gamete have?
23
How is variation produced in sexual reproduction?
The genetic information from each parent is mixed
What is asexual reproduction?
Involves one parent with no gametes joining
What process does Asexual reproduction use?
Mitosis
Why does asexual reproduction produce clones?
As there is no mixing of genetic information
What are the advantages of Sexual reproduction?
- Produces variation in offspring
- Allows us to use selective breeding
How is sexual reproduction allowing animals to produce variation in offspring an advantage?
- Means that if the environment changes it is likely that an organism in the species will have a survival advantage
- Variation decreases the chance of the whole species becoming extinct
How is sexual reproduction allowing animals to use selective breeding an advantage?
- Organisms with different desirable characteristics can be bred to produce offspring
- Speeds up natural selection
What are the disadvantages of Sexual reproduction?
- Time and energy are needed to find a mate
- It is not possible for an isolated individual
What are the advantages of asexual reproduction?
- Only one parent is needed
- Uses less energy + is faster
- Favourable conditions - lots of identical offspring can be produced
How does asexual reproduction use less energy?
As organisms don’t need to find a mate
What are the disadvantages of asexual reproduction?
- It does not lead to variation in a population
- The species may only be suited to one habitat
- Disease may affect all the individuals in a population
What is meiosis used to produce?
Haploid gametes
What is meiosis?
Reduction division in a cell in which the chromosome number is halved from diploid to haploid
What is DNA?
The material inside the nucleus of cells, carrying the genetic information of a living being
What is DNA made up of?
Nucleotides
What is a nucleotide made out of?
- Sugar
- Bases
- Phosphate group
What is the double helix held together by?
Weak hydrogen bonds between complementary base pairs
How are weak hydrogen bonds formed between bases?
Parts of DNA bases have slight electrical charges
A slightly negative charged part of one bases attracts a slightly positive part of another base = weak hydrogen bond
How many hydrogen bonds does Cytosine & Guanine produce?
3 hydrogen bonds
How many hydrogen bonds does Adenine & Thymine produce?
2
What does Adenine pair with?
Thymine
What does Guanine pair with?
Cytosine
What shape is DNA?
Double helix
What important information does DNA carry?
Genetic code - determines characteristics of a living organism
What type of molecule is DNA?
A polymer
What does the order of different bases form?
Genetic code
What is a gene?
A short section of DNA
What does each gene code for?
Many amino acids, which are joined together to make a specific protein
How many types of amino acids are there?
20
What is a genome?
All of the DNA in an organism
What are the aims of the Human genome project?
- To work out the order or sequence of all the three billion base pairs in the human genome
- To identify all the genes
- To develop faster methods for sequencing DNA
What has the Human genome project helped us understand the human body?
- Improved our understanding of the genes
linked to different types of disease - Treatment of inherited disorders
- Tracing human migration patterns from the past
Core practical: Extracting DNA
Describe the method you would use to extract DNA from a fruit?
1) Gently mix together some cold water, some salt and washing up liquid. Gently heat this mixture at a high temp for 5-10 minutes
2) Peel the skins of a fruit and chop into small pieces. Pulverise the fruit.
3) Add the solution from Step 1 to the fruit
4) Filter the solution using a few sheets of kitchen paper and a sieve. Pour the filtrate into a test tube
5) Add some pineapple juice to the filtrate and allow to rest for a few minutes
6) Add a few teaspoons of cold ethanol to the solution and wait a few minutes
Core practical: Extracting DNA
Why do we add ethanol?
Ethanol causes the DNA to precipitate out of the solution
Core practical: Extracting DNA
What is the expected observation of this practical?
A white mass should precipitate at the top of the tube after 10 minutes (this is the DNA)
Core practical: Extracting DNA
Why do we add a protease enzyme solution / pineapple juice?
This breaks down the proteins attached to the DNA - helps us to see it more clearly
How many bases code for an amino acid?
3
What determines what type of protein is produced?
The different types and order of amino acids
—>Therefore it is the order of bases in DNA that determine which proteins are produced
What are the steps that make up protein synthesis?
- Transcription
- Translation
What is a polypeptide chain?
Amino acid sequences
What are some uses of proteins?
- Enzymes
- Hormones
- Structural proteins
How are proteins used as hormones?
They carry messages around the body
How are proteins used as structural proteins?
They provide structure and are physically strong
How are proteins used as enzymes?
They act as biological catalysts to speed up chemical reactions occurring in the body
What is Transcription?
DNA is transcribed and an mRNA molecule is produced
What is Translation?
mRNA is translated and an amino acid sequence is produced
Where does Transcription occur?
Nucleus
Describe & explain transcription in protein synthesis
- Part of a DNA molecule unwinds
—> exposes the gene to be transcribed - RNA polymerase binds to a region of non-coding DNA just in front of the gene
- RNA polymerase then makes a complementary copy of the code from the gene
- mRNA molecule leaves the nucleus via a pore in the nuclear envelope
What does it mean for part of a ‘DNA molecule to unwind’ in transcription?
The hydrogen bonds between the complementary base pairs break
How does ‘RNA polymerase make a complementary copy of the code from the gene’?
By building a single-stranded nucleic acid molecule - mRNA
What is a polynucleotide?
Made up of many nucleotides linked together in a long chain
Give some examples of polynucleotides
- DNA
- RNA
What do RNA nucleotides contain instead of thymine?
Uracil (U)
Describe the structure of an RNA polynucleotide
- Alternating ribose sugars
- Phosphate groups linked together
- Nitrogenous bases of each nucleotide projecting out sideways
Where does Translation occur in protein synthesis?
Cytoplasm
Why must DNA first be transcribed into mRNA before it can be translated into a protein?
DNA cannot travel out of the nucleus to the ribosomes as it is too big to pass through the nuclear membrane
What is a codon?
Each triplet of bases on a mRNA molecule
Describe & explain translation in protein synthesis
- After leaving the nucleus, the mRNA molecule attaches to a ribosome
- tRNA molecules bind with their specific amino acids and bring them to the mRNA molecule on the ribosome
- The anticodon on each tRNA molecule pairs with a complementary codon on the mRNA molecule
- Peptide bond is then formed between the two amino acids
- Polypeptide chain is formed
What does the ribosome do after the mRNA molecule attaches onto it?
- The ribosome ‘reads’ the code on the mRNA in groups
- The ribosome translates the sequence of bases into a sequence of amino acids that make up a protein
Describe the structure of a tRNA molecule?
- Anticodon on one end
- A region where specific amino acid can attach at the other end
What is an anticodon?
A triplet of unpaired bases at one end
How many tRNA molecules can fit onto a ribosome at any one time?
2
What molecules are in the cytoplasm that is useful for protein synthesis?
- tRNA
- Amino acids specific to the tRNA
When does the process translation stop?
Until a ‘stop’ codon on the mRNA molecule is reached
What does mRNA stand for?
messenger RNA
What does tRNA stand for?
transfer RNA
What is a genetic variant?
Small changes in the order of bases that make up a strand of DNA
What is genotype?
Refers to the genes present in the DNA of an individual
What is phenotype?
Refers to the visible effects of those genes
What does non-coding mean?
The DNA bases do not code for the production of an amino acid
How does genetic variants in the non-coding regions of a gene affect the phenotype?
Influences the binding of RNA polymerase and altering the quantity of protein produced
Describe & explain how genetic variants in the ‘non-coding’ regions of a gene affect the phenotype?
- If a mutation happens in the non-coding region to which RNA polymerase attaches
—> Can affect the ability of RNA polymerase to bind to it - It can make it difficult for RNA polymerase to bind, less mRNA will be transcribed from the gene and less protein (that the gene codes for) will be produced
How does genetic variants in the coding regions of a gene affect the phenotype?
The gene may code for a different sequence of amino acids so it’ll alter the activity of the protein produced
What are the types of DNA mutations?
- Insertions
- Substitutions
- Deletions
What is substitutions?
One of the bases is changed for another random bas
What is insertions?
An extra base is inserted into the sequence
What is deletions?
One of the bases is deleted from the sequence
What is the issues with DNA mutations?
(insertion, deletions and substiutions)
It may change all the amino acids coded
What is an allele?
Different forms of a gene
What is a dominant allele?
Only one (out of the two alleles) is needed for it to be expressed and for the corresponding phenotype to be observed
What is a recessive allele?
Two copies are needed for it to be expressed and for the corresponding the phenotype to be observed
What is homozygous?
When both inherited alleles are the same
What is heterozygous?
When one of the inherited alleles is dominant and the other is recessive
What is a chromosome?
A structure found in the nucleus which is made up of a long strand of DNA
