b13 - reproduction Flashcards
how many chromosomes would you find in a human skin cell?
46
what does mitosis result in the formation of?
2 genetically identical daughter cells
difference between a gene and a chromosome?
chromosomes contain genes
gene is small section of DNA that codes for a specific protein/characteristic
by which process do bacterial cells divide?
binary fission
asexual reproduction
involves only one individual and the offspring is identical to the parent. there is no fusion of gametes or mixing of genetic information
- genes from one parent
- all clones to the parent - no variation
- only mitosis
- no gametes (sex cells) involved
sexual reproduction
- involves the fusion of male and female gametes (fertilisation) producing genetic variation in the offspring
- inherits a mixture of feature
- egg (23) + sperm (23) > zygote > embryo
- genes from two parents
- gametes are formed by meiosis
meiosis
2 stage process of cell division that reduces the number of chromosomes of daughter cells, involved in making gametes for sexual reproduction
diploid (46) > haploid (23) > then copies itself to make 4 daughter cells (instead of 2 like mitosis)
examples of organism that go through asexual reproduction
- strawberries
- fungi
examples of organism that go through sexual reproduction
- humans
- insects
advantages of asexual reproduction
- only one parent needed
- many identical offspring reproduced
- faster than sexual reproduction
- already has the features required to survive in its environment
disadvantages of asexual reproduction
- no variation
- susceptible to environmental change
advantages of sexual reproduction
- all offspring are different (variation)
- survival advantage if environment changes
disadvantages of sexual reproduction
- reliant on sperm and egg coming into contact
- slower than asexual reproduction
gametes in flowering plants
pollen and egg cells
gametes in animals
sperm and egg cells
gametes
genetic information for organisms that reproduce sexually
- a haploid because it has one set of chromosomes
- haploid number 23 (half the number of what would be expected)
how is sperm adapted to its function?
- mitochondria - gives it the energy to swim
- acrosome - head of the sperm that has digestive enzymes that digests the outer layer of the egg
- has a tail to swim streamlined
how is the egg adapted to its function
- has a protective outer layer
- is large so that it can be found by the sperm
- releases chemicals to attract the sperm (a conc gradient)
diploid
has two sets of chromosomes (46)
why is it important that the number of chromosomes halves during meiosis
- if it didn’t the embryo would have double the number of chromosomes - 92 instead of the normal 46
- so that the number of chromosomes is conserved
fertilisation
when the games fuse to form a zygote.
the zygote then starts to divide through mitosis
why are mutations in sex cells more serious than mutations in body cells?
- the mutation of a body cell can be easily solved by the body
- however, if that happens with a sex cell and is then fertilised - it can then lead to genetic problems
mitosis vs meiosis
- mitosis divides once but meiosis divides twice
- 2 cells produced by mitosis and 4 cells produced by 4
- mitosis has 46 chromosomes but meiosis has 23
- mitosis is used for making body cells; meiosis is used for making gametes
- mitosis happens in all parts of the body; meiosis happens only in the testes and ovaries
fungi
- made up of a mass of thin threads called hyphae
- the mass of the hyphae forms its visible structure of
reproduction in fungi
- asexual
- the fungi spores are produced by MITOSIS and they’re genetically identical to the parent
- some fungi reproduce sexually in unfavourable conditions
toadstool
an asexual fruiting body that is full of spores
why does it produce sexually in unfavourable conditions?
so that variation can take place and the offspring can adapt to any changes in the environment
are fungi haploid or diploid most of the time?
haploid
when do two hyphae join together?
when environmental conditions are unfavourable
when do fungi undertake meiosis?
after two hyphae have joined together
sexual reproduction in fungi
- some fungi reproduce sexually in unfavourable conditions. two hyphae from different fungi join and the nuclei fuse. so the new hypha has 2 sets of chromosomes
- it then undergoes meiosis to make haploid spores which are different from the original hyphae
- some of the spores may produce fungi better adapted to survive the adverse conditions
what type of pathogen is malaria?
protist
which two types of cells are targeted by malaria in humans?
liver cells and red blood cells
where does fertilisation of malaria take place?
in the stomach of the mosquito
where does the asexual reproduction of the malaria take place?
in the human host
what are the effects of malaria in humans?
fever, loss of blood, brain damage, coma, death
process of sexual production in the mosquito?
process of asexual reproduction in the human host
reproduction in plants
- flowers are the sexual reproductive organs of plants
- they make haploid gametes (pollen and egg cells) by meiosis that fuse to form diploid seeds that are genetically different to their parents
- many plants can also reproduce asexually eg. strawberry plants and daffodil bulbs. this involves only mitosis so the offspring are genetically identical to the parent.
- sexual reproduction is an advantage when flowers are destroyed or unfertilised
what is DNA and its structure?
- the molecule of inheritance - deoxyribonucleic acid
- encodes and holds genetic instructions/code for different proteins
- chromosomes and their genes are made of a molecule called DNA
- each chromosome is a very long molecule called DNA
- twisted ladder/ spiral shape = double helix
DNA nucleotides
- the backbone of the long strand of DNA is made of alternating sugar and phosphate molecules - attached to each sugar is one of four bases (A, T, C, G)
- the combination of a sugar, phosphate and a base is a nucleotide
- the DNA polymer is made of repeating nucleotide units/monomer
DNA bases
- the double helix ‘ladder’ of a DNA is held together by ‘rungs’ made from pairs of chemicals calls bases
- four types of bases A>T, C>G
- base pairs hold the two strands of the DNA helix together
- the sequence of the bases along the DNA molecules form genetic code
genomes
- all the complete genetic information of an organism
- includes all the chromosomes and the genetic material found in the mitochondria
- has the ability to make many different proteins from the same gene by using it in different ways, or by switching part of a gene on or off
- whole genome can now be sequenced in 24 hours
which is larger a gene or a chromosome
a chromosome
where in the cell is DNA produced to produce mRNA?
the nucleus
what is an allele?
gene or combination of genes that we inherit from our parents eg.
H - straight hair, h - curly hair
what is a genotype?
a combination of alleles that one has received from their parents - (Hh)
you can get different combinations - (hh) (HH) (Hh)
what is a phenotype?
what the genotype codes for; the actual characteristics/ result of a genotype
what is a dominant allele?
the capital letter - expressed in the phenotype
what is a recessive allele?
the lower case letter - not expressed in the phenotype unless it is a double recessive gene (hh)
genotype combinations EXAMPLE
straight hair = H
curly hair = h
(HH) - straight
(Hh) - straight
(hh) - curly - because double recessive gene
homozygous
hh - same letter (homozygous recessive)
HH - same letter (homozygous dominant)
heterozygous
different (letter) cases - Hh
punnet square
a diagram used to calculate the probability of the phenotype being expressed
examples of two genetically received diseases
- CYSTIC FIBROSIS - must be a double recessive gene (both parents must have it for it to be dominant and the child to have it)
- POLYDACTYLY - passed on by a dominant allele
where in the cells are proteins made?
ribosomes
what are some of the functions/uses of proteins in the body?
- to make new cells when you grow, and to replace old or damaged cells
- antibodies
- enzymes
what are proteins made up of?
amino acids
examples of proteins:
- ribosomes
- antibodies
- amylase
- respiration enzyme
- haemoglobin
what is RNA?
- has a single helix so that the bases can be read clearly during protein synthesis
- has uracil as one of its bases instead of thymine
- small section of DNA or gene that can eventually exit to the cytoplasm for protein synthesis
explain the order of protein synthesis
1) genes in the DNA produce a template for the protein (a subsection not all of the DNA)
2) the template reflects the sequence of bases but is small enough to fit through the nuclear pore
3) the template (mRNA) binds to the ribosome surface
4) the carrier molecule, each attached to a specific amino acid attach themselves to the template in the order given by the DNA
5) the amino acids are joined together to form proteins
6) the carrier molecules keep bringing specific amino acids to add to the growing protein chain in the correct order until the template is completed
7) the protein detaches from the carrier molecules and the carrier molecules detach from the template and return to the cytoplasm to pick up more amino acids
8) the protein chain then folds up in to the unique shape of the protein
how many bases code for an amino acid?
3
what brings amino acids to ribosomes?
tRNA or carrier molecule
why can’t DNA move into the cytoplasm?
the DNA is too big to move through the pores of the nucleus
what might happen if there was a mistake in the DNA or if one of the bases were changed?
a mutation in the cells - the structure of the sequence of DNA is changed
what is transcription?
making the mRNA or the template molecule from the DNA
what is translation?
carrier molecule (tRNA) brings the amino acids to be joined to ribosomes
what are simplified steps of protein synthesis?
DNA > transcripted > RNA > translated > protein
what is a codon?
a triplet of three bases
what does the amino acid on the tRNA depend on?
the three complementary bases attached to it
what happens after the tRNA delivers its amino acid?
it then goes and attached to another cell to redo the process
what is a non-coding region?
the parts of DNA in between the genes - involved in switching genes ‘on’ and ‘off’
when the gene is on it starts producing a protein
what is a substitution?
when a base is swapped for another base - sometimes this might change the amino acid but other times it might not. this varies dependin on the amino acid
what is an insertion?
if there is a change in sequence (the addition or deletion of a base) the whole protein will be different as it has different amino acids
what are the effects of a mutation?
1) no change in amino acids or a slight change which doesn’t affect the protein structure
2) altered protein, so the protein may not work (eg. the active site of the substrate may no longer fit the substrate)
3) mutation within a non-coding region nearby to a gene may affect the expression (production) of a protein
what happens if the mutation happens during mitosis?
it only affects a localised, isolated cells
what happens if the mutation happens during meiosis?
affects the whole organism (their offspring)
why does the mutation in meiosis affect the whole organism?
- mitosis is only regarding a cell but meiosis involves the gametes
what is sickle cell anaemia?
- genetically inherited
- one substitution in the haemoglobin, which changes the structure of the protein (in this case haemoglobin) so it can’t bind properly
how do mutations affect genes?
1) protein may be unchanged - active site is the same shape so works normally
2) active site shape changed so the substrate does not fit and doesn’t work
3) active site changed shape so a different substrate fits - catalyses a different reaction
sometimes it can have a severe effect on the person but sometimes it may not
are all mutations harmful?
no they’re not all harmful as some of them don’t change the structure of the protein therefore it doesn’t harm or affect the organism or some may be beneficial to the organism and allow them to adapt to survive eg. camouflage
how does DNA control the synthesis of proteins in a cell?
- the template (mRNA) is produced that reflects the sequence of bases in DNA of a single gene
- the template is small enough to leave the nucleus through pores in the nuclear membrane, and bind to the surface of ribosome
- carrier molecules (tRNA) in the cytoplasm, each attached to the a specific amino acid, attach themselves to the template in order given by the DNA until the template is completed
- amino acids join together to form a specific protein
- protein detaches from the carrier molecules , which detach from the template and return to cytoplasm to pick up more amino acids
- once protein chain is complete the molecule folds up to form a unique shape that will enable it to carry out its functions in the cell
