chapter 13 Flashcards
genes
sections of DNA that contain genetic code. store information that determines the activities and structure of the cell
consists of up to 1000 bases, possibilities are enormous
chromosomes
dna strands are bound to proteins called histones. each DNA is coiled around the histones so long molecules can fit into a small space
when a cell is about to divide, the coiled chromatin becomes even more tightly coiled to form chromosomes
DNA
deoxyribonucleic acid found in nucleus of the cell
contain genetic information that determines the structure of a cell and how it functions
steps of DNA replication
- double stranded DNA molecule unwinds and units by helicase (enzyme), and weak hydrogen bonds are broken
- primase is required to initiate/start replication. The primer helps DNA polymerase to know where to start copying
- DNA polymerase: binds to a single strand and helps create/build a complementary strand (using free nucleotides in nucleus) to know where to start copying
- ligase is needed to glue/seal DNA fragments together
- the DNA molecule is formed has one strand of the original parent DNA and 1 newly made strand
transcription
- takes place in the nucleus
- triggered by hormone that enters nucleus and binds to specific gene on DNA
- RNA polymerase then attaches to begin the process
- helicase makes the double stranded DNA molecule unzip to allow one of the DNA strands to be decoded (template strand)
RNA polymerase transcribes the bases on the template strand to make a complementary molecule of mRNA (uracil) - mRNA nucleotides floating around in the nucleus find their complement on the DNA strand and bond to gather due to base pair rule
sequence of bases tell RNaA polymerase to stop copying this release mRNA molecule - once the DNA segment has been copied by the mRNA bases, the mRNA strand separates from the DNA. mRNA contains complementary base sequence to original DNA
- introns are removed (Junk DNA)
- the mRNA leaves the nucleus via pore and enters the cytoplasm. it attaches to a ribosome for protein synthesis
- DNA zips up again to create the original double helix
translation
- takes place at a ribosome
- mRNA is read 3 codons at a time.
AUG is the start codon, ribosome start making protein, methionine can be removed later - tRNA delivers AA to the ribosomes, each tRNA carries a specific AA. the tRNA anticodon, will match with its complementary mRNA codon
- ribosome works its way down the strand of mRNA reading off the code. (tRNA is recycled, bringing in more AA) rRNA join AA together by forming a peptide bond
- as process continues, polypeptide chain is formed until a stop codon
- multiple copies of proteins are made as other ribosomes copy the first ribosome
- mRNA is recycles, broken up and nucleotides reused
- after translation, proteins are modified by folding and shortening them in a certain way (enzymes) transported to where the body needs
chromatin
in a cell that isn’t dividing, coiled DNA form an untangled network called chromatin
dna structure
building blocks are called nucleotides
each DNA consists of two strands of alternating sugars and phosphates with pairs of nitrogenous bases forming cross links between sugar molecules in the two strands
twisted into spiral shape (double helix)
base contains nitrogen atoms, bond between bases are weak hydrogen bonds
replication of DNA in interphase
two linked chains in DNA separate because bond between bases is weak
each separated sections half of the original and acts as a template for for nucleotides that form the other half using complementary bases
protein synthesis
amino acids joined to form chemical bonds that hold, AA together
joined in ribosome in cytosol of cell. DNA is too big to leave the nucleus so mRNA is used as it is small enough to go through nuclear pores
conversion of genetic code carried by DNA to an end product (protein)
genetic code
types of protein a cell makes is determined by it gens.
different genes are activated in different cells (insulin)
triplet codes for amino acids that are joined together at ribosomes
nucleosome
8 part histone structure
karyotype
photograph of chromosome organised by size shape and banding
lipid and carbohydrate synthesis
no genes to carry out instructions
made by enzymes (proteins) indirectly controlled by genes
mitochondrial DNA
in mitochondria
small circular molecules
has 37 genes
24 genes code for making tRNA molecules, 13 genes are instructions for making enzymes needed to make ATP
provides information which is needed for mitochondria to function
mitochondria
cells and mitochondria are codependent
inherited from mother as mDNA in sperm are destroyed in fertilisation
used for ancestry, evolution and forensics
disease: inability to produce sufficient energy to carry out simple tasks
epigenetic
study of changes in gene activity that don’t involve changes in gene code
epigenome: second set of instructions that interact with DNA that activate/suppress expression of certain genes
exposure to certain stimuli can change epigenome
acetylation
add acetyl group
cause DNA to unwind enhancing gene expression
methylation
adding a methyl group
cause DNA to coil more tightly silences or switches of gene
cell cycle
G1 phase: first growth, cells produce new proteins, grows and carries out its normal tasks
S phase: synthesis, DNA duplicates itself
G2 phase: second growth, short phase that involves preparation for cell division
M phase: mitotic, cell divides into two daughter cells
some cells leave cell cycle and stop dividing for years or rest of life. G0
interphase
period between nuclear divisions
G1,S,G2
DNA replicates
prophase
centrioles become visible early on, move to opposite ends of cell (poles) and microtubules radiate from them form framework of fibres called spindle
nucleolus disappears and nuclear membrane breakdown
chromatin threads of DNA coil to be seines chromosomes (2 chromatid joined at centre with centromere)
chromatids are identical to each other and tightly coiled
coiling makes it easier to distribute DNA to daughter cell
migrate to equator of cell
metaphase
chromatid line up at equator
centromere of each pair is attached to a spindle fibre
anaphase
each pair of chromatids separate at centromere
new chromosomes are pulled apart towards opposite poles of cell
telophase
two sets of chromosomes form tight groups at each pole
nuclear membrane forms around each group and nucleolus appears
spindle fibres disappear
chromosomes gradually uncoil to become chromatin
cytokinesis
while telophase occurs, cytoplasm begins to divide
furrow develops between two nuclei and deepens til it is cut in two
joined at centromere =
chromatid
not chromosomes
cancer
all cancers have common characteristics
when a tumour results form uncontrolled division of cells, don’t differentiate so the cancer cells can be identified
malignant: cells spread throughout the body
benign: don’t spread to other parts of body but can press on surrounding tissues
carcinogen: factors that can trigger cancer (UV, Xray, HPV, ionising radiation, chemicals)
cervical cancer
caused by HPV, transmitted through genital skin contact during sex
Pap test: cells from cervix detect changes in cells that may develop into cancer
breast cancer
mammogram: Xray picture that detects tumours, even really small ones
bowel cancer
in large intestine
FOBT faecal occult blood test: detects traces of blood caused by polyps/ cancer. polyps can lead to cancer
Colonoscopy
prostate cancer
no screening
DRE, digital rectal examination: feeling prostate for irregularities
PSA, prostate specific antigen:checks blood for a specific protein produced by prostate gland rising levels can indicate tumour
biopsy: small sample of tissue that can be checked for cancer cells
